You are probably the only one on TH-cam that described the a/c pressure switches. And you make it so simple. Thank you so much. Awesome teacher. You just answered so many questions that I had.
Awesome video explaining how system and switches work. You nailed it. Important takeaway - if your relay is clicking, all pressure switches and VCM are working correctly. This is time saver.
This is by far is one of the best video tutorials! I have been a diehard DIYer all my life and have been trying to trouble shoot my ac compressor suddenly not get any power. This has solved that issue. Thanks so much for the help.
This has to be one of the very best technicians who posts videos like this on You Tube!!! I have seen several videos He has posted and His methods are really good...
This is the best video on TH-cam explaining the 2 switches. I'm an electrician so this makes perfect sense and for anyone that doesn't have a electrical background just follow this man's instructions step by step and you will be able to troubleshoot your issue. If you cant read schematics dont sweat it and just ignore that part of the vid. Great job to the man that created this vid.
Nice explanation and for using the description of “Interrupter” as well. Having the light and DMM are great visuals for those who learn better this way. I will finish the last few minutes but the P/S switch also effects the circuit. Depending on the manufacture, model and year, but the A/C compressor is interrupted and shut off at high speeds. This can be done using an external switch on the gas pedal, speed sensor at the compressor clutch with steel / iron reluctor and Hall-Effect switch or PM generator that produces an A/C voltage signal, buffered by diodes & electronics shutting the compressor off. Speed or the drivers request for speed reduces damage to the compressor during high RPM’s and helps with performance or fuel economy both during certain conditions. It is nice to see a professional tutorial on the subject. I added info the would make the entire subject harder and perhaps loose some viewers. ASE Master Tech since 1978 - Retired
I used to wire industrial control panels. Your explanation regarding normally closed/normally open pressure switches is very clear. In our schematics we sometimes show the contacts at rest. What we do is indicate on the schematic that the normally closed switch is closed when pressure is above ### and the normally closed is open above ### pressure.
One of the best AC trouble shooter videos I've ever seen. Exactly what I needed to continue trouble shooting my 1977 F-350 Diesel AC problem. Thanks, look forward to other videos.
Thank you for an excellent video! You gave me courage to tackle my A/C issue. I found that when briefly bypassing the low pressure switch, the compressor did turn, indicating a need for a charge and probably a leak fix. Five stars from me today!!! :)
This was the most informative information I have received, and I have gone through hundreds of them here on youtube, you predicated what the other gentleman spoke, you both are on the same page. I did what you and he said and it works, 1988 Lincoln Continental MK VII LSC. Thank you a thousand times.
You video worked. My compressor was clicking on and off fast. Changed the low pressure switch and it just unscrews without loosing the freon. Then it let me add freon. I did jump the switch for awhile to get it to suck up the freon. Thankd
Smart men! Thank you. Is was very useful for me. Videos like this should be underlined as very well designed and performed educational videos. Thank you again for your time and efforts!
I'm working on making a Frankenstein ac system work, and I've gotta say that this video really cleared things up for me!! Thank you very much! Keep up the good work!
This is exactly the sort of video that I crave (most of yours are). Please keep the in-depth videos coming. I always take something from your videos that help me in my job (if!). A very sincere thanks to you sir!
This helped me figure out a problem in my wiring that I'd be struggling with for a few days. The explanation of the wiring diagram is what did it. Thanks for the thoroughness!
how come all the mechanics that i know, they pretend to know and they do not know shit, this guy in the video is the one you want to know for all your mechanical problems, He is the MAN, and thank you very much Mr.
Thanks for the video D !! It helped me in the field i followed all your training and checked compressor wiring harness all the way back to the PDC everything good .. I found low pressure switch stuck open circuit .. After checking the wiring diagram first i bridged the the plug and the AC system started to work .. The vehicle was a 2006 Jeep Liberty 3.7 V6
I have a 2006 GMC sierra pick up truck. The ac quit blowing cold air and I notice the compressor clutch was not pulling in. I checked the fuses in the inside compartment and they were good. I checked the fuses I pulled the relay and checked the coil with an ohm meter and it appeared to be good. 85 Ohms across the coil just like several others that were working. I jumped the contacts on the relay socket and the compressor relay pulled in and the ac blew cold air. So because the fuse was blown and it worked jumped out I though maybe the relay contacts were bad for some reason. I replaced it and had no change. All this time I was getting a 12 volt signal to the relay coil socket. So per your video I set out to check the pressure switches. The low one is a 2 wire and the high one is a 3 wire. I unplugged the 2 wire pressure switch and metered the contacts and had continuity. I plugged the low pressure switch cable back in and all of the sudden the compressor clutch pulled in. The air now seems to be working correctly and blowing cold air. Do I have a problem coming that I should look into?
Very informative video! Thank you Sir! Just need some help on my car. Ac clutch stays engaged when ac is on. It does not cycle. Cooling is not a problem. Cabin temperature sensor is fine. Freon charge is okay. I am not sure if it is the cycling switch control that’s making it not to disengage. TIA
hi duane nice videos, I learn a lot from it, this just a refresh, where are the AC low and hi pressure switches located, the low on the low side ? and the hi on the hi side of the system? please correct me if I'm wrong ,if not tell me , thank u duane
Man your video was so informative , it helped me well understand the a/c circuitry , next week id check out my toyota hilux a/c system for ps malfunction and share the results , although the documentary says its a double pressure switch i think it works the same way as you explaind but no idea why theyve called it a double switch!
Thanks, was trying to find a video to replace them. I was hoping the end the instructor would actually replace one, 20 minutes about a basic on off pressure switch, noda about replacing it. schrader valves makes total sense, wish the instructor would have mentioned it, and do we need to change the pressure or is it correct out of the box? ?? need more info on replacing it. 20min video on turning off a lightbulb.
The previous compressor, clutch went bad and it did not cool anymore, It actually broke.Before replacement I flushed the complete system independently. Recaptured the Freon . I replaced with a new compressor, expansion valve, seals. I used a can with a gauge and charged up to 35 psi , everything was working great and cooling. Afterwards I made a mistake of following a generic a/c charge guideline and topped it to 55. I heard the compressor locked up?, sounded lick when a compressor kicks on but slightly louder. The high side on the gauge dropped to 60 and stayed there. Then the car stopped cooling. Removed the Freon and pulled another vacuum, charged to 35 psi and the compressor seems like it kicks on when u press a/c button inside, but the Freon does not flow through the system. After that I have run the compressor about 15-20 min trying to diagnose. My plan is to replace with a new compressor, new a/c switch (pressure switch located next to the high side) and pull a vacuum(1 hour) and recharge correctly. I assume if this is all done again , all should work. Unless the a/c amplifier went bad? It seems its not necessary to flush the system again, since there was no knocking sounds in new compressor and it really did not kick in after over charge. (electrical)-----. To me it seems that the job of the a/c amplifier is to manage power to the compressor and work with a/c(pressure) switch through the wiring and make the compressor run (electrical). Seems that these compressors are smart , have a safety mechanism inside, maybe can be disactivated or maybe they just lock up when over charged. So essentially if electrical is good, the mechanical(compressor and components) then the system should work. Am I missing anything else??. This 2007 is more complicated than a standard car where you only have one cable that runs to the compressor, where you can connect a 12v wire from battery to make the compressor run to check it. This car has 2 leads in the harness and leads me to believe different voltage, cant really be bypassed any where? Also you cant bypass the a/c switch , it has 3 cables.
good lesson well spoken and to the point. I get it. my clutch isnt pulling in and now I can test my low and high pressure sensors. thought I was stumped when my fuse proved good and relay was working.thanks
Thank You! My 1996 K2500 has the schematic you first showed with Logic Controller in cab supplying 12VDC to LPS then HPS then to VCM. I keep blowing the power transistor in the Logic Controller (A/C control module in cab). The power transistor supplies the 12VDC when the "A/C Button" is pressed. I suspect a bare wire ground somewhere along the Light Green/Dark Green/Dark Green with white daisy chain to the VCM. I am confused by a third pressure switch on my A/C compressor that appears to be another LPS. So I have: LPS at Firewall Receiver, HPS on back of A/C compressor all per the factory manual just like the first schematic you showed. But, I have this third LPS (??) also on the A/C compressor that does not appear to be part of my path (which confused the heck out of me while trying to use my DVOM to trace the path from cab to underhood VCM looking for an intermittent ground). What is that LPS for? Thank you for this excellent example and for providing two very different examples of how this LPS/HPS system can be wired. Very educational.
I have reviewed the diagram again and I can not see that second LPS you are referring to. I would love to help if possible but I need you to be more specific. Is it possible you could send me a picture of it please ? email to. dumar5907 @ gmail.com
Thanks for the classes but I have a a/c wiring diagram question. On the diagram the wire comes from the high pressure switch and splice into a wire that goes from the control module to a solid state box. What is this solid state box? I am getting power except between a good high pressure switch and the clutch, I jumped a wire between the high pressure switch etc. Whats in the center? Solid state?
Very good video. My only question which I did not see him explain tho. If there is no pressure in the system say you change compressor and have vacuum out. The clutch does not engage, so how do I get the clutch to engage (compressor turn on) to refill fridgerant? Is this when I should look at bypassing the switches?
That's interesting how different systems work. On older Peterbilts a ground is sent from the dash control through hi and low pressure switches strait to a relay once the control panel is turned on. The key switch feeds power to terminal 86 and 30 is always hot. If there is pressure in the system the ground goes thru hi and lo AC switches and reaches term 85 in the relay and sends 13+ V out 87 to turn the compressor on. Nothing goes through the ECM. Todays trucks might be fed through the ECM though. Its kind of hard to come up with 450 Psi to know for sure that the high pressure switch is working. There really needs to be a way to test that. A Nitrogen tank would do it with the correct connections. Nitrogen is even more handy to have around to test for AC leaks also with soapy spray and pressuring the system. I've seen slow leaks not show up until about 170 PSI. Some leaks take less than 25 psi and boom instant bubbles.
Toyota Camry 1996 2.2 Engine 4 cylinder. The condenser fan continuously runs even when the switch is off. I changed the AC relay- the temperature sensor and even the fan switch. But, it stills continues to run. Any advice?
My question is if I'm not receiving power to the compressor what should I be checking next? I was able to test the compressor by placing a temporary connection from the battery and the compressor did come one. I also tried to short the two wire from the low pressure switch and the compressor didn't come on, but I did receive a 12 volt reading on those two wires. Please help.
I have a 2000 ford ranger. The a.c will attempt to work on startup of the truck, for 3 seconds the clutch will engage and will only if reengage if i turn off the truck and start it again. paperclip trick don't work (pressure switch) refrigerant is good, i know this by running 2 wires directly from the battery to the clutch while the truck is running. the reading on the low side was 35 and the high side 200
Thank you sir for the vid. But i have different case with me here 2010 explorer 4.0L the compressor is always engaged and never cycles..? Properly Charged and Pressures are 40 on the low 235psi on the high 1- Something weard i noticed whenever i check rest peeaaure engine off, Low side is like 240 or so everytime. ! The cooling inside the cabin is great around 40-42F 2- How much charge does this vehicle take..? Hood sticker is not there, destroyed i guess. 3- does over charging cause the compressor to stay on all the time..? 4- does the cooling fan have anything to do with the compressor cycling ? In case the fan is faulty for example?? 5- which component exactly is responsible for the cycling of the compressor, other than the cabin temp sensor..?? 6- for the life of me, i couldn't find where it lives, i searched everywhere but i couldn't locate it. Pls. Help me, im stuck with this challenge vehicle, i should call it. 🌷
Hi. Your video is great.When I mashed the A/C switch the light flashed three times and that was all I got so I changed the a/c high pressure sensor on my 2009 Chevrolet Impala. I have searched and searched but can not find a a/c low pressure sensor. Is there a a/c low pressure sensor?
The high pressure switch could also pass these test's yet still not function 100%, is that correct?? Reason asking is, a GM vehicle I have would provide cool air but at certain times and temps, it would not be cool enough, the air in the vents was above 40 degrees. All system checks passed yet sometimes the A/C worked like a charm and in other times it would barely cool even though the freon was fully charged. An A/C guy found the high pressure switch could be the issue so he replaced it and all worked solid from then on. Cost was $40 installed.
hello, great explanation, I know is a bit old video but I wonder if a VUE 2008 that uses only one cycling switch can it be tested like that?, can I replace it without having a gas leak?
Hello Dwayne!!! Can you provide some direction on what to check for when the AC fans don't come on right away on a 2003 Grand Prix 3.8 liter? Clutch engages right away and there is adequate refrigerant in the system. But fans come on several minutes late and then the in-cabin air is cooled properly.
so my question is, if either the low or high pressure switches are bad will they burn out the fuse from the fuse box? thanks hope to hear from you soon...
Where is the low pressure switch typically located? Is it on the intake side of the compressor or the output side? When you see one of these switches, how do you recognize which switch you are looking at?
just look for a switch on the low side. follow the low side until you see it. Could be on the canister near the compressor or at the end of the line. or like in the middle of the run of the line,just depends on the car.
I just made a post but forgot to mention I noticed the a/c compressor clutch was not engaging and the fans were off so I then changed the a/c high pressure sensor (It was called a Pressure Transducer). I vacuumed the system as the system was empty. Before charging the system, will the freon start the a/c clutch? And Is there a a/c low pressure sensor?
2011 Honda fit- Ac compressor clutch will not engage. Applied 12 v at relay socket, this will engage the clutch manually. Bench tested relay, applied 12 v and got continuity across the load side. Tested relay socket with multimeter, on load side, 12v available , other pin has continuity to compressor. On trigger side, constant 12v source ( reversed polarity -12v for some reason) whether or not AC switch is on. Tested pressure sensor on Low side of compressor line with multimeter, continuity checked. Tested temperature protection switch at compressor, continuity checked. Tried disconnecting battery on the car for ECU reset, tested all fuses I could think of, FAN, SUB FAN, MG CLUTCH, AC. There are several relays in the actual fuse box which have no labels, unable to test those because I don't know what they do, auxiliary relay box in engine bay contains 3 relays, fan x2 and AC Clutch, applied 12 v all click when voltage is applied. Totally lost on what to do next, resistance across the clutch coil is 3 ohms and it works when 12v is directly applied either by battery to clutch or jumping the relay socket. Any help would be greatly appreciated.
I have an interesting one for you, 1986 gm, if I turn key switch on (engine off) and turn on a/c the fan blower works perfect. But when the engine starts the fan blower will not work at all. I ran test light to blower motor and only powers up as long as engine is not running. Have you seen this before?
thank you so much for this useful information but, are all cars have two switches? because I don't find in mine just one! I have Chevrolet Equinox 2008
i have a 2006 chevy colorado 4 cyl and my a/c clutch comes on and off periodically. i read on 355nation that the low pressure switch, gm part# 13502759 or ac delco # 15-51258 may be the problem. i unplugged mine, cleaned it with electrical spray then reattached it. then it worked better. Now on day 2 it started to cut on and off again during stops signs/ idle but runs fine during driving. I will replace it because it is a cheap fix $20, besides the 2 cans of freon i put in that still didnt work.
Dear RNW you are great and you take your time to explain things well. But I have Question about my system which is confusing and I have not seen solution to it on you tube Maybe you can Help. I have Tundra 2001 it had front right side body damage affected the fender, RF headlight and air filter housing and bent the condenser, also replaced the Radiator, and fan was broken also. All were fixed. System had pressure even after accident. First situation was Low pressure low (15-20), and High pressure High over 250psi, and clutch engage and disengage frequently we added Freon just a little high side went way up and low stayed the same, pursuant to Toyota Diagnostic table, indicated Blockage in the Receiver Dryer or expansion valve, we replaced both, we also tested all the line connection for leak, after replacement and testing condenser for leak we got to situation 2. Now the condenser have minor bent but holding pressure, the low is steady normal at 40 psi, and the high side went too high 275 and kept increasing to about to 350- to 375 close to 400psi and we did not even put one small can and clutch engages all the time without stop. Do you suspect the high pressure sensor not closing the circuit and causing all of the issues?
My clutch wont engage. Before replacing I watched this video and see that the high pressure sensor can be culprit and can be tested with ohmmeter..so I pulled sensor, 3 prong, and all 3 lead options read OPEN. So as described in video the sensor defective. No continuity. So I bought new sensor BUT also reads no continuity. What did I miss?? THANKS
Really good video to watch and learn.I m currently having intermitent cool air output from my 2004 Toyota 3sgte.Last week the condensor was jet sprayed washed with a cleaning agent.Yes the air is cooler but the intermitence is just the same. After watching this video I am now suspicious if this switches are causing it.
gracias muchas gracias esta class me alludo a comprender y lo iso muy bien entendible facil para probar aunque no able Español se entiende con la ilustracion. thanks a lot this class help me I'm learning more thanks again.
I have a question, I have no power going to my 2001 Ford Expedition 5.4 L. I have been doing some troubleshooting the last few days and came up with this so far. Both high and low pressure switches have 12 V going through them to power the PCM. Since the PCM is powered, when I checked my 4 terminals on my AC compressor relay I found a ground(assuming from the PCM like video says) and 2 12 V leads, both coming from their own fuse source.
i bought a c-class mercedes 2004 and found out that there is no refrigerant on the system, i vacuumed it out for 30 minutes and holds 750 microns and start charging R134a at Low Side service port but the compressor won't engage and not even pulling refrigerant. Low Side needle 45 PSI and High Side Neddele 26 PSI. Is it bad compressor?
Hi I have a question, I diagnosed the harness of the high pressure switch to be bad. and made a straight cable to bypass it hence trouble shooting the harness is not easy. I want to know how bad i risk to damage the compressor by keeping this. is the A/C pressure switch turning on and off all the time? or only when things are really bad
My A/C is nice and cool blowing when I first start the vehicle. It will run a while then, warm air will blow. I'll turn it off. After a few minutes, it will be cold again. I do this off/on dance until I get too irritated and drive with the windows down the rest of the way home. What's up? Is it a bad pressure switch? Is it the high or low switch? The vehicle is a 2008 Ford Ranger.
2001 Hyundai Sonata 4 cyl - I thought at first it needed a recharge of R134a , it only took 1/3 of a can I noticed the clutch wasn't turning on the compressor , so what's next where are the high and low pressure switches located or the compressor cut off switch , I checked all the 10 amp fuses all good? if I check the resistance across the 2 wires coming out of the AC compressor clutch what should it read?
Hello. On my case clutch is turning, everything thing seems good but I don't have cold ❄️ air. I still have 460g freon on the system. I verified all fuse and relay. I don't just have cold air.
My car is blowing hot air on idle when my ac is on, it also blows about 60 degrees F, when driving (I used a thermometer) I changed my condenser, evacuated the system and I vacuumed out the system. My fans work and my clutch is engaging. When connected to the manifold gauges for static pressure, both low and high are reading 80 psi. When the car is running and AC is on, my low side is 30 and my high side is 40 . I can’t tell if I need a switch or some type of sensor?
static pressure of 80 is on the low side, and if the compressor is indeed running and the high side only reads 40, you are low on refrigerant, or the compressor isn't capable of getting the high side pressure up enough.
![3 Symptoms Of A Bad AC Pressure Switch [HIGH OR LOW]](http://i.ytimg.com/vi/Va3_3Xk4ZHk/mqdefault.jpg)
You are probably the only one on TH-cam that described the a/c pressure switches. And you make it so simple. Thank you so much. Awesome teacher. You just answered so many questions that I had.
Awesome video explaining how system and switches work. You nailed it. Important takeaway - if your relay is clicking, all pressure switches and VCM are working correctly. This is time saver.
This is by far is one of the best video tutorials! I have been a diehard DIYer all my life and have been trying to trouble shoot my ac compressor suddenly not get any power. This has solved that issue. Thanks so much for the help.
Thanks for commenting
old school; from the basic principles to the schematics. Simply one of the best I've seen around.
This has to be one of the very best technicians who posts videos like this on You Tube!!! I have seen several videos He has posted and His methods are really good...
I've been studying exercises for jumping higher and found a fantastic resource at Enyeto Jump Plan (check it out on google)
This is the best video on TH-cam explaining the 2 switches. I'm an electrician so this makes perfect sense and for anyone that doesn't have a electrical background just follow this man's instructions step by step and you will be able to troubleshoot your issue. If you cant read schematics dont sweat it and just ignore that part of the vid. Great job to the man that created this vid.
Thanks, I appreciate you taking the time to comment
@@realfixesrealfast My honor. I was well deserved. Thank you for doing the video.
Nice explanation and for using the description of “Interrupter” as well. Having the light and DMM are great visuals for those who learn better this way. I will finish the last few minutes but the P/S switch also effects the circuit. Depending on the manufacture, model and year, but the A/C compressor is interrupted and shut off at high speeds. This can be done using an external switch on the gas pedal, speed sensor at the compressor clutch with steel / iron reluctor and Hall-Effect switch or PM generator that produces an A/C voltage signal, buffered by diodes & electronics shutting the compressor off. Speed or the drivers request for speed reduces damage to the compressor during high RPM’s and helps with performance or fuel economy both during certain conditions.
It is nice to see a professional tutorial on the subject. I added info the would make the entire subject harder and perhaps loose some viewers.
ASE Master Tech since 1978 - Retired
Thanks for your input Dean, It always helps to add more information
I used to wire industrial control panels. Your explanation regarding normally closed/normally open pressure switches is very clear. In our schematics we sometimes show the contacts at rest. What we do is indicate on the schematic that the normally closed switch is closed when pressure is above ### and the normally closed is open above ### pressure.
One of the best AC trouble shooter videos I've ever seen. Exactly what I needed to continue trouble shooting my 1977 F-350 Diesel AC problem. Thanks, look forward to other videos.
Thank you for an excellent video! You gave me courage to tackle my A/C issue. I found that when briefly bypassing the low pressure switch, the compressor did turn, indicating a need for a charge and probably a leak fix. Five stars from me today!!! :)
This was the most informative information I have received, and I have gone through hundreds of them here on youtube, you predicated what the other gentleman spoke, you both are on the same page. I did what you and he said and it works, 1988 Lincoln Continental MK VII LSC. Thank you a thousand times.
One of the best ac videos on here. Thank you for explaining lingo along with terms. AWESOME!!! Thanks again!
I am a former ASE certified mechanic, and, in my modest opinion, this guy could very well charge for this teaching on the matters! Very good!
Thanks, I appreciate you taking the time to comment
I just want to thank you for all the videos you do; they really help a lot of people.
You video worked. My compressor was clicking on and off fast. Changed the low pressure switch and it just unscrews without loosing the freon. Then it let me add freon. I did jump the switch for awhile to get it to suck up the freon. Thankd
Smart men! Thank you. Is was very useful for me. Videos like this should be underlined as very well designed and performed educational videos. Thank you again for your time and efforts!
Very instructive. If ever you have time, would it be possible to explain a 4 pin high pressure switch? How to test it.Thank you
I'm working on making a Frankenstein ac system work, and I've gotta say that this video really cleared things up for me!! Thank you very much! Keep up the good work!
Well done! Bringing the basics to the layman! Great video👍
This is exactly the sort of video that I crave (most of yours are). Please keep the in-depth videos coming. I always take something from your videos that help me in my job (if!). A very sincere thanks to you sir!
Very good informative video I'm glad I watched the whole thing.
This helped me figure out a problem in my wiring that I'd be struggling with for a few days. The explanation of the wiring diagram is what did it. Thanks for the thoroughness!
Thank you for the excellent explanation and visual and mechanical demonstration.
how come all the mechanics that i know, they pretend to know and they do not know shit, this guy in the video is the one you want to know for all your mechanical problems, He is the MAN, and thank you very much Mr.
His a not a mechanic, his a professional auto electrician
I've seen pressure switches with 3 wires.
How do those work?
Are they a combination low, high pressure switch?
Thanks for the video D !! It helped me in the field i followed all your training and checked compressor wiring harness all the way back to the PDC everything good .. I found low pressure switch stuck open circuit .. After checking the wiring diagram first i bridged the the plug and the AC system started to work .. The vehicle was a 2006 Jeep Liberty 3.7 V6
so if the ac switch dont work...compressor clutch wont come on???? some one please tell me
I have a 2006 GMC sierra pick up truck. The ac quit blowing cold air and I notice the compressor clutch was not pulling in.
I checked the fuses in the inside compartment and they were good. I checked the fuses I pulled the relay and checked the coil with an ohm meter and it appeared to be good. 85 Ohms across the coil just like several others that were working. I jumped the contacts on the relay socket and the compressor relay pulled in and the ac blew cold air. So because the fuse was blown and it worked jumped out I though maybe the relay contacts were bad for some reason. I replaced it and had no change.
All this time I was getting a 12 volt signal to the relay coil socket. So per your video I set out to check the pressure switches. The low one is a 2 wire and the high one is a 3 wire. I unplugged the 2 wire pressure switch and metered the contacts and had continuity. I plugged the low pressure switch cable back in and all of the sudden the compressor clutch pulled in. The air now seems to be working correctly and blowing cold air.
Do I have a problem coming that I should look into?
Very informative video! Thank you Sir! Just need some help on my car. Ac clutch stays engaged when ac is on. It does not cycle. Cooling is not a problem. Cabin temperature sensor is fine. Freon charge is okay. I am not sure if it is the cycling switch control that’s making it not to disengage. TIA
hi duane nice videos, I learn a lot from it, this just a refresh, where are the AC low and hi pressure switches located, the low on the low side ? and the hi on the hi side of the system? please correct me if I'm wrong ,if not tell me , thank u duane
Well done HVAC 101 training, back to basics. Thank you for sharing.
This helped a lot. I just purchased an a/c set up for my truck at a salvage yard but the wiring was all disconected.
Thanks so much for good , clear ,and complete instructions. Just doesn't get any better than this ! ----Ernest E. Johnson
Very informative..Your a very good diagnostic man
Thank you so much for this wonderful informative video, perhaps tomorrow I can diagnose my Civic.
Thank you very much sir , but I have one question: does a bad high pressure switch turn off compressor clutch? And How?
It does turn off compressor clutch. The clutch wont run without a good high pressure switch. How It interrupts that circuit.
Man your video was so informative , it helped me well understand the a/c circuitry , next week id check out my toyota hilux a/c system for ps malfunction and share the results , although the documentary says its a double pressure switch i think it works the same way as you explaind but no idea why theyve called it a double switch!
Can't make it any more clear than you have explained. Great video.
Thanks, was trying to find a video to replace them. I was hoping the end the instructor would actually replace one, 20 minutes about a basic on off pressure switch, noda about replacing it. schrader valves makes total sense, wish the instructor would have mentioned it, and do we need to change the pressure or is it correct out of the box? ?? need more info on replacing it.
20min video on turning off a lightbulb.
The previous compressor, clutch went bad and it did not cool anymore, It actually broke.Before replacement I flushed the complete system independently. Recaptured the Freon . I replaced with a new compressor, expansion valve, seals. I used a can with a gauge and charged up to 35 psi , everything was working great and cooling.
Afterwards I made a mistake of following a generic a/c charge guideline and topped it to 55. I heard the compressor locked up?, sounded lick when a compressor kicks on but slightly louder. The high side on the gauge dropped to 60 and stayed there. Then the car stopped cooling. Removed the Freon and pulled another vacuum, charged to 35 psi and the compressor seems like it kicks on when u press a/c button inside, but the Freon does not flow through the system. After that I have run the compressor about 15-20 min trying to diagnose.
My plan is to replace with a new compressor, new a/c switch (pressure switch located next to the high side) and pull a vacuum(1 hour) and recharge correctly. I assume if this is all done again , all should work. Unless the a/c amplifier went bad? It seems its not necessary to flush the system again, since there was no knocking sounds in new compressor and it really did not kick in after over charge.
(electrical)-----. To me it seems that the job of the a/c amplifier is to manage power to the compressor and work with a/c(pressure) switch through the wiring and make the compressor run (electrical). Seems that these compressors are smart , have a safety mechanism inside, maybe can be disactivated or maybe they just lock up when over charged. So essentially if electrical is good, the mechanical(compressor and components) then the system should work.
Am I missing anything else??. This 2007 is more complicated than a standard car where you only have one cable that runs to the compressor, where you can connect a 12v wire from battery to make the compressor run to check it. This car has 2 leads in the harness and leads me to believe different voltage, cant really be bypassed any where? Also you cant bypass the a/c switch , it has 3 cables.
good lesson well spoken and to the point. I get it. my clutch isnt pulling in and now I can test my low and high pressure sensors. thought I was stumped when my fuse proved good and relay was working.thanks
Thank You! My 1996 K2500 has the schematic you first showed with Logic Controller in cab supplying 12VDC to LPS then HPS then to VCM. I keep blowing the power transistor in the Logic Controller (A/C control module in cab). The power transistor supplies the 12VDC when the "A/C Button" is pressed. I suspect a bare wire ground somewhere along the Light Green/Dark Green/Dark Green with white daisy chain to the VCM. I am confused by a third pressure switch on my A/C compressor that appears to be another LPS. So I have: LPS at Firewall Receiver, HPS on back of A/C compressor all per the factory manual just like the first schematic you showed. But, I have this third LPS (??) also on the A/C compressor that does not appear to be part of my path (which confused the heck out of me while trying to use my DVOM to trace the path from cab to underhood VCM looking for an intermittent ground).
What is that LPS for? Thank you for this excellent example and for providing two very different examples of how this LPS/HPS system can be wired. Very educational.
I have reviewed the diagram again and I can not see that second LPS you are referring to. I would love to help if possible but I need you to be more specific. Is it possible you could send me a picture of it please ? email to. dumar5907 @ gmail.com
How do you test a high pressure switch with 3 wires?
only reason I clicked
man im in the same situation
Need more teachers like him, awesome job sir
Superb way of explaining electric circuit's and the testing of,, thank you so much.
This is the best video of ever seen on the air conditions it really helped me out a lot keep up the good work man
Thanks for the classes but I have a a/c wiring diagram question. On the diagram the wire comes from the high pressure switch and splice into a wire that goes from the control module to a solid state box. What is this solid state box? I am getting power except between a good high pressure switch and the clutch, I jumped a wire between the high pressure switch etc. Whats in the center? Solid state?
Very good video. My only question which I did not see him explain tho. If there is no pressure in the system say you change compressor and have vacuum out. The clutch does not engage, so how do I get the clutch to engage (compressor turn on) to refill fridgerant?
Is this when I should look at bypassing the switches?
yes because the switches operate on pressure, negative or positive. Bypass the switches So you are in charge of their position.
As a fellow engineer, I really appreciate your simplistic message.
Thanks, always good to see someone recognizes the value
That's interesting how different systems work.
On older Peterbilts a ground is sent from the dash control through hi and low pressure switches strait to a relay once the control panel is turned on. The key switch feeds power to terminal 86 and 30 is always hot.
If there is pressure in the system the ground goes thru hi and lo AC switches and reaches term 85 in the relay and sends 13+ V out 87 to turn the compressor on. Nothing goes through the ECM. Todays trucks might be fed through the ECM though.
Its kind of hard to come up with 450 Psi to know for sure that the high pressure switch is working. There really needs to be a way to test that. A Nitrogen tank would do it with the correct connections. Nitrogen is even more handy to have around to test for AC leaks also with soapy spray and pressuring the system. I've seen slow leaks not show up until about 170 PSI. Some leaks take less than 25 psi and boom instant bubbles.
thanks for your comments. Systems are always changing theses days.
Toyota Camry 1996 2.2 Engine 4 cylinder.
The condenser fan continuously runs even when the switch is off.
I changed the AC relay- the temperature sensor and even the fan switch.
But, it stills continues to run.
Any advice?
My question is if I'm not receiving power to the compressor what should I be checking next?
I was able to test the compressor by placing a temporary connection from the battery and the compressor did come one.
I also tried to short the two wire from the low pressure switch and the compressor didn't come on, but I did receive a 12 volt reading on those two wires.
Please help.
I have a 2000 ford ranger.
The a.c will attempt to work on startup of the truck, for 3 seconds the clutch will engage and will only if reengage if i turn off the truck and start it again.
paperclip trick don't work (pressure switch)
refrigerant is good, i know this by running 2 wires directly from the battery to the clutch while the truck is running.
the reading on the low side was 35 and the high side 200
Thank you sir for the vid.
But i have different case with me here
2010 explorer 4.0L the compressor is always engaged and never cycles..?
Properly Charged
and Pressures are 40 on the low
235psi on the high
1- Something weard i noticed whenever i check rest peeaaure engine off,
Low side is like 240 or so everytime. !
The cooling inside the cabin is great around 40-42F
2- How much charge does this vehicle take..?
Hood sticker is not there, destroyed i guess.
3- does over charging cause the compressor to stay on all the time..?
4- does the cooling fan have anything to do with the compressor cycling ?
In case the fan is faulty for example??
5- which component exactly is responsible for the cycling of the compressor, other than the cabin temp sensor..??
6- for the life of me, i couldn't find where it lives, i searched everywhere but i couldn't locate it.
Pls. Help me, im stuck with this challenge vehicle, i should call it. 🌷
Hi. Your video is great.When I mashed the A/C switch the light flashed three times and that was all I got so I changed the a/c high pressure sensor on my 2009 Chevrolet Impala. I have searched and searched but can not find a a/c low pressure sensor. Is there a a/c low pressure sensor?
Mister you are a MAESTRO.... excellent video thank you
The high pressure switch could also pass these test's yet still not function 100%, is that correct?? Reason asking is, a GM vehicle I have would provide cool air but at certain times and temps, it would not be cool enough, the air in the vents was above 40 degrees. All system checks passed yet sometimes the A/C worked like a charm and in other times it would barely cool even though the freon was fully charged. An A/C guy found the high pressure switch could be the issue so he replaced it and all worked solid from then on. Cost was $40 installed.
Great presentations! Very educational. Thank you for sharing your knowledge in a very practical manner.
Your welcome. Thanks for your comments
I have no power to low pressure switch
Thank you sir !! nice tutorial very straight forward and detailed. ..
Yes, he'll answer a specific problem for you on his website for $34.95!! Real nice guy!!
hello, great explanation, I know is a bit old video but I wonder if a VUE 2008 that uses only one cycling switch can it be tested like that?, can I replace it without having a gas leak?
Hello Dwayne!!! Can you provide some direction on what to check for when the AC fans don't come on right away on a 2003 Grand Prix 3.8 liter? Clutch engages right away and there is adequate refrigerant in the system. But fans come on several minutes late and then the in-cabin air is cooled properly.
Whats the part # for the hi pressure switch. And vehicle. I cant find o e for a chevy project. Thanks
How come some AC compressors dont have a clutch but a switch instead. How do these systems work or turn on and off??
OhhhhHHH!!! Thank you! What if it has 3 wires?
This is such a good example and teach video! Thank you!
so my question is, if either the low or high pressure switches are bad will they burn out the fuse from the fuse box? thanks hope to hear from you soon...
Where is the low pressure switch typically located? Is it on the intake side of the compressor or the output side? When you see one of these switches, how do you recognize which switch you are looking at?
just look for a switch on the low side. follow the low side until you see it. Could be on the canister near the compressor or at the end of the line. or like in the middle of the run of the line,just depends on the car.
I just made a post but forgot to mention I noticed the a/c compressor clutch was not engaging and the fans were off so I then changed the a/c high pressure sensor (It was called a Pressure Transducer). I vacuumed the system as the system was empty. Before charging the system, will the freon start the a/c clutch? And Is there a a/c low pressure sensor?
I like your videos, you take the time to track things down logically.
2011 Honda fit- Ac compressor clutch will not engage. Applied 12 v at relay socket, this will engage the clutch manually. Bench tested relay, applied 12 v and got continuity across the load side. Tested relay socket with multimeter, on load side, 12v available , other pin has continuity to compressor. On trigger side, constant 12v source ( reversed polarity -12v for some reason) whether or not AC switch is on. Tested pressure sensor on Low side of compressor line with multimeter, continuity checked. Tested temperature protection switch at compressor, continuity checked. Tried disconnecting battery on the car for ECU reset, tested all fuses I could think of, FAN, SUB FAN, MG CLUTCH, AC. There are several relays in the actual fuse box which have no labels, unable to test those because I don't know what they do, auxiliary relay box in engine bay contains 3 relays, fan x2 and AC Clutch, applied 12 v all click when voltage is applied.
Totally lost on what to do next, resistance across the clutch coil is 3 ohms and it works when 12v is directly applied either by battery to clutch or jumping the relay socket.
Any help would be greatly appreciated.
I have an interesting one for you, 1986 gm, if I turn key switch on (engine off) and turn on a/c the fan blower works perfect. But when the engine starts the fan blower will not work at all. I ran test light to blower motor and only powers up as long as engine is not running. Have you seen this before?
Love these videos. i learn so much. idk why but i like electrical work.
thank you so much for this useful information
but, are all cars have two switches? because I don't find in mine just one!
I have Chevrolet Equinox 2008
Verry good presentation simple and to the point.
This was actually a great A/C Switch Video! 2 thunbs Up!!!
i have a 2006 chevy colorado 4 cyl and my a/c clutch comes on and off periodically. i read on 355nation that the low pressure switch, gm part# 13502759 or ac delco # 15-51258 may be the problem. i unplugged mine, cleaned it with electrical spray then reattached it. then it worked better. Now on day 2 it started to cut on and off again during stops signs/ idle but runs fine during driving. I will replace it because it is a cheap fix $20, besides the 2 cans of freon i put in that still didnt work.
Dear RNW you are great and you take your time to explain things well. But I have Question about my system which is confusing and I have not seen solution to it on you tube Maybe you can Help. I have Tundra 2001 it had front right side body damage affected the fender, RF headlight and air filter housing and bent the condenser, also replaced the Radiator, and fan was broken also. All were fixed. System had pressure even after accident. First situation was Low pressure low (15-20), and High pressure High over 250psi, and clutch engage and disengage frequently we added Freon just a little high side went way up and low stayed the same, pursuant to Toyota Diagnostic table, indicated Blockage in the Receiver Dryer or expansion valve, we replaced both, we also tested all the line connection for leak, after replacement and testing condenser for leak we got to situation 2. Now the condenser have minor bent but holding pressure, the low is steady normal at 40 psi, and the high side went too high 275 and kept increasing to about to 350- to 375 close to 400psi and we did not even put one small can and clutch engages all the time without stop. Do you suspect the high pressure sensor not closing the circuit and causing all of the issues?
My clutch wont engage. Before replacing I watched this video and see that the high pressure sensor can be culprit and can be tested with ohmmeter..so I pulled sensor, 3 prong, and all 3 lead options read OPEN. So as described in video the sensor defective. No continuity. So I bought new sensor BUT also reads no continuity. What did I miss?? THANKS
Really good video to watch and learn.I m currently having intermitent cool air output from my 2004 Toyota 3sgte.Last week the condensor was jet sprayed washed with a cleaning agent.Yes the air is cooler but the intermitence is just the same.
After watching this video I am now suspicious if this switches are causing it.
What was the problem????????
2 wire simple want to figure out 3 and 4 wire transponders
gracias muchas gracias esta class me alludo a comprender y lo iso muy bien entendible facil para probar aunque no able Español se entiende con la ilustracion. thanks a lot this class help me I'm learning more thanks again.
what is the common issue of compressor relay pin 86 is no negative switching to engage relay coil.
realy it is fully educated post thanks lot for rich information you had posted
excellent teaching. simply explain a/c system
I
I have a question, I have no power going to my 2001 Ford Expedition 5.4 L. I have been doing some troubleshooting the last few days and came up with this so far. Both high and low pressure switches have 12 V going through them to power the PCM. Since the PCM is powered, when I checked my 4 terminals on my AC compressor relay I found a ground(assuming from the PCM like video says) and 2 12 V leads, both coming from their own fuse source.
🙂 Great video, very well explained and easy to understand. It helped me. Thanks 👍
i bought a c-class mercedes 2004 and found out that there is no refrigerant on the system, i vacuumed it out for 30 minutes and holds 750 microns and start charging R134a at Low Side service port but the compressor won't engage and not even pulling refrigerant. Low Side needle 45 PSI and High Side Neddele 26 PSI. Is it bad compressor?
I have a 2001 suburban. the ac clutch is staying on with the truck turned off. what are your thoughts on troubleshooting or problem
I feel like I had a college class on auto AC systems
You're Video is very helpful and cannot be explained any better thank you so much for for your time
Hi I have a question, I diagnosed the harness of the high pressure switch to be bad. and made a straight cable to bypass it hence trouble shooting the harness is not easy. I want to know how bad i risk to damage the compressor by keeping this.
is the A/C pressure switch turning on and off all the time? or only when things are really bad
Can you jump a high pressure switch?
My A/C is nice and cool blowing when I first start the vehicle. It will run a while then, warm air will blow. I'll turn it off. After a few minutes, it will be cold again. I do this off/on dance until I get too irritated and drive with the windows down the rest of the way home.
What's up? Is it a bad pressure switch? Is it the high or low switch? The vehicle is a 2008 Ford Ranger.
really good video, couldn't be more clear. thanks for sharing knowledge.
2001 Hyundai Sonata 4 cyl - I thought at first it needed a recharge of R134a , it only took 1/3 of a can I noticed the clutch wasn't turning on the compressor , so what's next where are the high and low pressure switches located or the compressor cut off switch , I checked all the 10 amp fuses all good?
if I check the resistance across the 2 wires coming out of the AC compressor clutch what should it read?
Good video
where do you get the correct electrical diagram. I have three different diagrams and none are the same for my truck
Hello. On my case clutch is turning, everything thing seems good but I don't have cold ❄️ air. I still have 460g freon on the system. I verified all fuse and relay. I don't just have cold air.
you're spot on! I like your videos! Doug in Orlando Fl. Walt Disney Fleet mechanic.
Is it hard on a ac system to leave it on when turning off your vehicle? I’ve had this debate with my buddy who is a mechanic.
wow ...you're great men. it help me to understand how it thank you.
My car is blowing hot air on idle when my ac is on, it also blows about 60 degrees F, when driving (I used a thermometer) I changed my condenser, evacuated the system and I vacuumed out the system. My fans work and my clutch is engaging. When connected to the manifold gauges for static pressure, both low and high are reading 80 psi. When the car is running and AC is on, my low side is 30 and my high side is 40 . I can’t tell if I need a switch or some type of sensor?
static pressure of 80 is on the low side, and if the compressor is indeed running and the high side only reads 40, you are low on refrigerant, or the compressor isn't capable of getting the high side pressure up enough.