Great series on the C4! I have a 94 convertible and that was the first year for the glass rear window in the convertible, it also has a rear window defogger grid. I would think prior to 94, the convertible would have the mirror button in the HVAC control head as they wouldn't have had a defogger in the plastic rear window. Thanks again for the C4 videos!
Thanks, appreciate it👍. I agree the graphic may have changed with the introduction of the heated glass rear window. I'll have to take a closer look at my 90-93 controllers again.
Yes my 93 convertible has plastic rear window. So that switch is for the side mirror in mine and thanks for the content every bit of information helps.
Great explanation of the system. It took me a bit of reading through the manual to understand the different settings such as heater for my 92. One thing I notice is if I have it on auto or bi-level on a cool morning, the car drips a lot of condensation underneath. Was quite concerning the first time I noticed this.
Hey Jason, thanks for the positive feedback. Glad you enjoyed the video👍. The electronic A/C system is a bit more complex then it appears at first glance. Having the manual on hand is always a great tool for a Corvette owner.
I just bought my first corvette two days ago!! But I noticed that the ac cluster does not work, when I turn the lights on for the inside the little screen just turns orange with no info being displaced. Any ideas what it could be? I already check and changed the fuse with no luck. It’s a 94 vette
Hey CG, a non-responsive AC controller with no display other than the backlight is most likely an internal failure of the unit. You can send yours out for rebuild, or just replace.
Last Plenum pull I did caused the AC to stop working . All functions work , just won't turn the AC on . Not sure what I missed putting it back together but will check those 3 sensors you mentioned . Had a garage look at it and they had to top up the 134a but they also had to jumper the AC to get it to come on . No idea what they did to get it to run . Probably going to have to pull the Plenum again . It may be the controllers but it was working before the Plenum pull . May have to get electronic replacement parts from Batee Thanks for the vid .
Interesting side effect of a plenum pull. My first thought would be to look at the blower module at the firewall next to right resr corner of the plenum. It's possible the harness was damaged when the plenum was removed and is not feeding the power circuit to the module.
@@VetteSource Good point . I did look over the harness . I had to replace the AC Coil seal . The soft foam molding was all rotted so it was having lots of air leakage . I had pulled the plenum 3 times before this last one and everything worked with the previous pulls . Thanks for the tip . Will go over it again with a volt meter to see if things are being energized
@@VetteSource Power is going to fan modules . All fuses are good also . Will pull plenum next week . Has to be either a vacuum leak I missed or something I forgot to connect . 🤔🤨😐
My 95 convertible has the rear window defrost button, rather than a mirror button- but it also defrosts the mirros at the same time. Also, if you hold the windshield defrost button and the floor vent buttons simultaneously, it'll split between those two vents- I think they called it "defog".
Good information, thanks for sharing. I didn't touch on some of the more advanced functional aspects of the late C4 unit due to time constraints, so it's good to have that information out there for people to see.
I'm working on a '91 convertible which is new to me. I'm not getting power to my climate control system. I get no green light or lighted display. I've tried two other heads and have no power to them either. But those are for coupes? Where should I look to get power to my unit?
Hey Mitchell, power to the HVAC control head is fed through the dash harness via a fuse inside the passenger side fusebox. With key in the "on" position, you should have 12 volts at the HVAC connector. Check the HVAC fuse and let me know what you find👍.
Any way to jump the fan motor to always run on high. i had someone change out the controller to fix the coupling sucking in problem where it cut off the vacuum but when i got it back the fan speed on ten is running about on 5. to slow out the front vents. Thanks Rob
Hey Rob, putting a jumper in the system had caused many C4 Corvettes to burn to the ground, so I don't recommend it. If the fan speed is slower than it should be, I would suggest looking at the blower module first, and then check the fan motor for resistance. If it's still not blowing out the correct vents you could have a problem with the AC programmer located above the gas pedal.
my Corvette cannot press the ac control button that freezes on the face, which turns off even the compressor, it only works for the glass and the feet, has anyone experienced this?
You have what's known as "sticky" buttons. They will do this with time and infrequent usage. You can fix this by taking the unit out, dismantling the circuit board from the back, and using a pencil eraser on the backside of the buttons. Amazingly simple fix, but it gets overlooked most of the time.
I have a 1994 convertible with 61,000 miles. My climate controls act up, won’t respond etc. I tore it down a few years ago and sprayed electronic spray on the terminals as suggested by a video, and it did start working normal. Now it’s acting up again. My CD player has never worked and recently I only get sound out of my right side speakers. I don’t see an adjustment for right to left just front to rear. It’s little things like this that make me want to sell the car sometimes. I’m also trying to diagnose a surging idle when cold, improves when it warms up but barely surges. I can’t find a shop where anybody knows more than me to get it diagnosed. No trouble codes pop up. I’m in the Atlanta area if anybody knows a Corvette expert. I’ve owned the car since 1999. The previous owner sold it when the warranty ran out. Thanks
Hey Tracy, sounds like you are experiencing some of the normal features inherent in owing a 25 year old car. With the Corvettes, it can become even more frustrating since they were pretty technology heavy for the time, and the electronics aren't the easiest to troubleshoot. I would recommend purchasing a factory service manual set off ebay. There is a ton of information inside, and will lead to you to a proper diagnosis most of the time.
@@VetteSourceyes I have both GM manuals, they were not cheap. They are not the easiest of reads. They jump around a lot section to section. Thanks for your reply.
Yep, for some reason it was always optional equipment. There are even late C4 and early C5s out there with manual ac. I think I have a few of the manual control heads on my shelf, but don't get asked about them very often.
Hey Paul, you should be able to hit the "auto" button along the bottom row. If it's not activating, the button may be sticking which is a common problem. Try the other buttons after the auto, and see if you get any response. Let me know how it turns out👍
I wondered. Obviously the earlier C4’s had a similar, though cruder bulkier looking, electronic HVAC head. But both heads are called C68. I was wondering if they were plug compatible. I.e. if you had a up to 89 and want to swap it out for this one… would it work?
For sure, there's not a whole lot of interchangeability on the C4 stuff. They always seemed to find a way to make running changes and upgrades over the C4 production run.
@@VetteSource I’m all for upgrades, but what happened to GMs mania for commonality and reuse!! (Or would that way leed to cheap plastic switches with aluminum plating.)
It’s cold but I can’t get it to manually come out the vents in the dash. It cools the windshield first. Is there any way I can get it to come of the dash vents?
Sounds like you have a A/C programmer issue. It is a black box mounted on the firewall above the gas pedal and controls the blend doors to redirect the airflow where you want it. Unfortunately the blend actuators are in a tight spot that you can't get to unless you pull much of the dash apart.
@@VetteSource or remove the drivers seat. you can get it that way and get rid of the couplings that flatten out over time, too soft and stop vacuum from pulling through the controller. That will fix the issue he is having and check a vacuum t on the intake, they crack and you will lose vacuum under an engine load and the doors will move and come back.
I think the vacuum t off the intake serves a different function, but I may be misremembering. The main vacuum source for the AC programmer originates from the vacuum reservoir located in the LF inner wheelwell, beside the headlight relay. That hard vacuum line feeds back through the engine harness through the firewall into the dash harness. I don't have my FSM in front of me, so I don't remember the exact routing off the top of my head.
wow that diagnostics secret is really freaking cool! I was geeking out over the speedo doing that, im blown away by these neat tidbits thank you!
Hey Jared, glad your enjoyed it. I'll keep plugging away at the videos for you guys.
Great series on the C4! I have a 94 convertible and that was the first year for the glass rear window in the convertible, it also has a rear window defogger grid. I would think prior to 94, the convertible would have the mirror button in the HVAC control head as they wouldn't have had a defogger in the plastic rear window. Thanks again for the C4 videos!
Thanks, appreciate it👍. I agree the graphic may have changed with the introduction of the heated glass rear window. I'll have to take a closer look at my 90-93 controllers again.
Yes my 93 convertible has plastic rear window. So that switch is for the side mirror in mine and thanks for the content every bit of information helps.
Good deal, thanks for confirming👍.
Thank you for all your informative videos. You’re a wealth of knowledge.
No problem, CT. Glad you find them enjoyable👍
great review as usual Thank you VetteSource.
Thanks, appreciate it👍
You just Saved me 6 Months of Guessing what's What! 👍👌
Excellent, glad to hear I could be of assistance👍
Great explanation of the system. It took me a bit of reading through the manual to understand the different settings such as heater for my 92. One thing I notice is if I have it on auto or bi-level on a cool morning, the car drips a lot of condensation underneath. Was quite concerning the first time I noticed this.
Hey Jason, thanks for the positive feedback. Glad you enjoyed the video👍. The electronic A/C system is a bit more complex then it appears at first glance. Having the manual on hand is always a great tool for a Corvette owner.
I hope you have a good Sunday as well.
👍
I just bought my first corvette two days ago!! But I noticed that the ac cluster does not work, when I turn the lights on for the inside the little screen just turns orange with no info being displaced. Any ideas what it could be? I already check and changed the fuse with no luck. It’s a 94 vette
Hey CG, a non-responsive AC controller with no display other than the backlight is most likely an internal failure of the unit. You can send yours out for rebuild, or just replace.
@@VetteSource dang that sucks. Thanks for the help though
Last Plenum pull I did caused the AC to stop working . All functions work , just won't turn the AC on . Not sure what I missed putting it back together but will check those 3 sensors you mentioned . Had a garage look at it and they had to top up the 134a but they also had to jumper the AC to get it to come on . No idea what they did to get it to run . Probably going to have to pull the Plenum again .
It may be the controllers but it was working before the Plenum pull . May have to get electronic replacement parts from Batee
Thanks for the vid .
Interesting side effect of a plenum pull. My first thought would be to look at the blower module at the firewall next to right resr corner of the plenum. It's possible the harness was damaged when the plenum was removed and is not feeding the power circuit to the module.
@@VetteSource Good point . I did look over the harness . I had to replace the AC Coil seal . The soft foam molding was all rotted so it was having lots of air leakage .
I had pulled the plenum 3 times before this last one and everything worked with the previous pulls . Thanks for the tip . Will go over it again with a volt meter to see if things are being energized
@@VetteSource Power is going to fan modules . All fuses are good also . Will pull plenum next week . Has to be either a vacuum leak I missed or something I forgot to connect . 🤔🤨😐
Yep, I would think so. Let me know how it turns out👍
@@VetteSource Turns out it's the Controller Module
This car got a lotta hate, but I own one and it's a GREAT car.
They're incredible cars. If people want to believe the nonsense that they're no good, let 'em miss out👍
very helpful thank you
Thanks Max, glad to hear it👍
My 95 convertible has the rear window defrost button, rather than a mirror button- but it also defrosts the mirros at the same time. Also, if you hold the windshield defrost button and the floor vent buttons simultaneously, it'll split between those two vents- I think they called it "defog".
Good information, thanks for sharing. I didn't touch on some of the more advanced functional aspects of the late C4 unit due to time constraints, so it's good to have that information out there for people to see.
I'm working on a '91 convertible which is new to me. I'm not getting power to my climate control system. I get no green light or lighted display. I've tried two other heads and have no power to them either. But those are for coupes? Where should I look to get power to my unit?
Hey Mitchell, power to the HVAC control head is fed through the dash harness via a fuse inside the passenger side fusebox. With key in the "on" position, you should have 12 volts at the HVAC connector. Check the HVAC fuse and let me know what you find👍.
Any way to jump the fan motor to always run on high. i had someone change out the controller to fix the coupling sucking in problem where it cut off the vacuum but when i got it back the fan speed on ten is running about on 5. to slow out the front vents. Thanks Rob
Hey Rob, putting a jumper in the system had caused many C4 Corvettes to burn to the ground, so I don't recommend it. If the fan speed is slower than it should be, I would suggest looking at the blower module first, and then check the fan motor for resistance. If it's still not blowing out the correct vents you could have a problem with the AC programmer located above the gas pedal.
@@VetteSource Thanks!
Good stuff!
Thanks Richard, glad you enjoyed it👍
One thing, if you want legs and windows same time, hit leg and window putton at the same time.
Nice👍, but you gotta tell me.what a putton is first.
I mean button not putton😀 you must push same time both buttons
Gotcha, just giving you a hard time👍. Have a great Sunday.
😀 thanks👍
my Corvette cannot press the ac control button that freezes on the face, which turns off even the compressor, it only works for the glass and the feet, has anyone experienced this?
You have what's known as "sticky" buttons. They will do this with time and infrequent usage. You can fix this by taking the unit out, dismantling the circuit board from the back, and using a pencil eraser on the backside of the buttons. Amazingly simple fix, but it gets overlooked most of the time.
I have a 1994 convertible with 61,000 miles. My climate controls act up, won’t respond etc. I tore it down a few years ago and sprayed electronic spray on the terminals as suggested by a video, and it did start working normal. Now it’s acting up again. My CD player has never worked and recently I only get sound out of my right side speakers. I don’t see an adjustment for right to left just front to rear. It’s little things like this that make me want to sell the car sometimes. I’m also trying to diagnose a surging idle when cold, improves when it warms up but barely surges. I can’t find a shop where anybody knows more than me to get it diagnosed. No trouble codes pop up. I’m in the Atlanta area if anybody knows a Corvette expert. I’ve owned the car since 1999. The previous owner sold it when the warranty ran out. Thanks
Hey Tracy, sounds like you are experiencing some of the normal features inherent in owing a 25 year old car. With the Corvettes, it can become even more frustrating since they were pretty technology heavy for the time, and the electronics aren't the easiest to troubleshoot. I would recommend purchasing a factory service manual set off ebay. There is a ton of information inside, and will lead to you to a proper diagnosis most of the time.
@@VetteSourceyes I have both GM manuals, they were not cheap. They are not the easiest of reads. They jump around a lot section to section. Thanks for your reply.
great info!
Thanks, Mako👍
My 1986 has electronic, I was shocked to see sliders in my 1988. I was wrong in my assumption that all 86 and newer was electronic.
Yep, for some reason it was always optional equipment. There are even late C4 and early C5s out there with manual ac. I think I have a few of the manual control heads on my shelf, but don't get asked about them very often.
I have a 91 C4 how do I turn it back on after hitting the off botton
Hey Paul, you should be able to hit the "auto" button along the bottom row. If it's not activating, the button may be sticking which is a common problem. Try the other buttons after the auto, and see if you get any response. Let me know how it turns out👍
@@VetteSource thank you the button was stuck
Great, glad to hear it worked out.
I wondered. Obviously the earlier C4’s had a similar, though cruder bulkier looking, electronic HVAC head. But both heads are called C68. I was wondering if they were plug compatible. I.e. if you had a up to 89 and want to swap it out for this one… would it work?
Hey Kelly, unfortunately the control systems, blend door actuator, and software programming are completely different so they aren't interchangeable
@@VetteSource
No surprised, but too bad.
Given the modules number hadn’t changed I hoped. ;)
Thanks.
For sure, there's not a whole lot of interchangeability on the C4 stuff. They always seemed to find a way to make running changes and upgrades over the C4 production run.
@@VetteSource
I’m all for upgrades, but what happened to GMs mania for commonality and reuse!! (Or would that way leed to cheap plastic switches with aluminum plating.)
Thank you
No problem, anytime👍
The sensor outside stays 25 degrees when it's 95 outside
Definitely somethings not reading correctly. Have you checked the senor bolted to the lower radiator housing at the front of the car?
I just bought a 96. That air is stupid. Mine works like shit.
Congrats on the purchase. Is the air coming out warmer than it should, or just not through the vents that are facing you?
It’s cold but I can’t get it to manually come out the vents in the dash. It cools the windshield first. Is there any way I can get it to come of the dash vents?
Sounds like you have a A/C programmer issue. It is a black box mounted on the firewall above the gas pedal and controls the blend doors to redirect the airflow where you want it. Unfortunately the blend actuators are in a tight spot that you can't get to unless you pull much of the dash apart.
@@VetteSource or remove the drivers seat. you can get it that way and get rid of the couplings that flatten out over time, too soft and stop vacuum from pulling through the controller. That will fix the issue he is having and check a vacuum t on the intake, they crack and you will lose vacuum under an engine load and the doors will move and come back.
I think the vacuum t off the intake serves a different function, but I may be misremembering. The main vacuum source for the AC programmer originates from the vacuum reservoir located in the LF inner wheelwell, beside the headlight relay. That hard vacuum line feeds back through the engine harness through the firewall into the dash harness. I don't have my FSM in front of me, so I don't remember the exact routing off the top of my head.
Too bad you don't do any c6 videos.
I'll get to them eventually. Lots of ground to cover with so many years of Corvette production. Thanks for watching👍