A/C question.
Thread Starter
Intermediate
Joined: May 2008
Posts: 27
Likes: 0
From: Clearwater FL
A/C question.
My a/c blows ice cold all the time - everything seems to work fine. Except when it gets real hot out. Like 95+, 140 closed inside kinda hot. When it gets real hot the a/c will blow cold for a few moments and then I will hear a click or pop sound - just once - and then it will blow heat out. Not the fan blowing natural hot summer air - I mean heated air.
Anyone familiar with this? May have an idea what is occuring here?
95 stock.
Thank you. E
Anyone familiar with this? May have an idea what is occuring here?
95 stock.
Thank you. E
Pro
Joined: May 2006
Posts: 637
Likes: 0
Might be on the edge of being to low on freon. As soon as the computer detects a certain low pressure it shuts off. Maybe the computer didn´t detect "low pressure" when it was colder. Checked for codes in the acc screen (where you read the temp) or do you have the manual ac? Auto ac; press and hold the temp up/down switches for 6 sec. then press the fan switch (1991) and you should get codes. -00 means everything OK.
Thread Starter
Intermediate
Joined: May 2008
Posts: 27
Likes: 0
From: Clearwater FL
Might be on the edge of being to low on freon. As soon as the computer detects a certain low pressure it shuts off. Maybe the computer didn´t detect "low pressure" when it was colder. Checked for codes in the acc screen (where you read the temp) or do you have the manual ac? Auto ac; press and hold the temp up/down switches for 6 sec. then press the fan switch (1991) and you should get codes. -00 means everything OK.
So I guess I should go to my mechanic with this info huh?
Thanks. E
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
I’m assuming you have the C68 auto control unit rather than the manual.
With the problem happening, check to see if the compressor is turning and cycling. Then check the accumulator and fat line to the evaporator by touching them. If they are cold, the freon portion of the A/C is working OK. If it is really blowing hot air it sounds like the heat actually came on and there could be a blend door related problem selecting the air from the heater core rather than the evaporator unit.
If that’s the case or what ever result you get, post it for further assistance. Finding out some basics might help you fix it or be more knowledgeable if you have to go to a shop. There are other things you can check but have to know these results first so don’t send you off in a wrong direction or waste time.
With the problem happening, check to see if the compressor is turning and cycling. Then check the accumulator and fat line to the evaporator by touching them. If they are cold, the freon portion of the A/C is working OK. If it is really blowing hot air it sounds like the heat actually came on and there could be a blend door related problem selecting the air from the heater core rather than the evaporator unit.
If that’s the case or what ever result you get, post it for further assistance. Finding out some basics might help you fix it or be more knowledgeable if you have to go to a shop. There are other things you can check but have to know these results first so don’t send you off in a wrong direction or waste time.
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
There are several safety devices on an AC system.
One of them will shut the AC down if the high-side pressure goes too high.
One thing that can cause the high-side pressure to go too high is blockage in front of the radiator/condenser assembly.
The C4 is notorious for accumulating debris in front of the radiator/condenser.
I would check to see if there is junk accumulated in front of the radiator.
Tom Piper
One of them will shut the AC down if the high-side pressure goes too high.
One thing that can cause the high-side pressure to go too high is blockage in front of the radiator/condenser assembly.
The C4 is notorious for accumulating debris in front of the radiator/condenser.
I would check to see if there is junk accumulated in front of the radiator.
Tom Piper
Safety Car
Joined: Oct 2007
Posts: 3,816
Likes: 0
From: :45 minutes from everywhere / E-I-E-I-O
Might be on the edge of being to low on freon. As soon as the computer detects a certain low pressure it shuts off. Maybe the computer didn´t detect "low pressure" when it was colder. Checked for codes in the acc screen (where you read the temp) or do you have the manual ac? Auto ac; press and hold the temp up/down switches for 6 sec. then press the fan switch (1991) and you should get codes. -00 means everything OK.
OP says it's not just fresh air, but HEAT.
You sure about that, OP?
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
Pro
Joined: May 2006
Posts: 637
Likes: 0
Thanks for the response. Yes, auto a/c. I tried what you said to get the codes and it did not give any codes. Then I held the fan up and down buttons (instead of the temp up and down buttons) and, without hitting the fan button, it stated -00. Sounds like I got their but in a different way perhaps?
So I guess I should go to my mechanic with this info huh?
Thanks. E
So I guess I should go to my mechanic with this info huh?
Thanks. E
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
That what why I was targeting on the blend door and its operation.
Last edited by pcolt94; May 27, 2008 at 01:45 PM.
Melting Slicks
Joined: Feb 2005
Posts: 2,135
Likes: 0
From: Sebastian Florida
St. Jude Donor '06
I have the same problem, there is no heat coming on. You are either low on freon or you have air in the system, mine has air in it from when I had a leak. Have the system vacuumed out and then recharge, my pressure was fine. But you could see a ton air bubbles in the system.
Thread Starter
Intermediate
Joined: May 2008
Posts: 27
Likes: 0
From: Clearwater FL
Absolutely sure that it is heat and NOT hot Florida fresh fan air. You put your hand right up there and it about feels like it's going to burn. My passenger confirms this diagnosis as well.
Le Mans Master
Joined: Jan 2006
Posts: 5,620
Likes: 206
From: Orlando FL
I believe you when you say heat.
You should check for cold pipes as just to reinforce what I think is the problem and the compressor is running correctly.
The blend door operation can be checked by removing the blower module in the evaporator case and view the door with a flashlight. Turn the key on and have someone else run the temp control from 60 to 90. See if the door swings back and forth. If it does not move proper, investigate. If it does move, drive to cool position and see if it stays there.
I also assume when you press the RECL button, air comes out of the top vents properly
You should check for cold pipes as just to reinforce what I think is the problem and the compressor is running correctly.
The blend door operation can be checked by removing the blower module in the evaporator case and view the door with a flashlight. Turn the key on and have someone else run the temp control from 60 to 90. See if the door swings back and forth. If it does not move proper, investigate. If it does move, drive to cool position and see if it stays there.
I also assume when you press the RECL button, air comes out of the top vents properly
Thread Starter
Intermediate
Joined: May 2008
Posts: 27
Likes: 0
From: Clearwater FL
I believe you when you say heat.
You should check for cold pipes as just to reinforce what I think is the problem and the compressor is running correctly.
The blend door operation can be checked by removing the blower module in the evaporator case and view the door with a flashlight. Turn the key on and have someone else run the temp control from 60 to 90. See if the door swings back and forth. If it does not move proper, investigate. If it does move, drive to cool position and see if it stays there.
I also assume when you press the RECL button, air comes out of the top vents properly
You should check for cold pipes as just to reinforce what I think is the problem and the compressor is running correctly.
The blend door operation can be checked by removing the blower module in the evaporator case and view the door with a flashlight. Turn the key on and have someone else run the temp control from 60 to 90. See if the door swings back and forth. If it does not move proper, investigate. If it does move, drive to cool position and see if it stays there.
I also assume when you press the RECL button, air comes out of the top vents properly
Any idea what kind of fix this would be? Expense wise? Complicated wise? I am not a mechanic but I have one.
Safety Car
Joined: Oct 2007
Posts: 3,816
Likes: 0
From: :45 minutes from everywhere / E-I-E-I-O
If it IS heat, the duct door is the sound you are hearin'.
Where is the sound comin' from? Engine area? Passenger dashboard area?
What happens if you manipulate the temp control (and nothin' else)???
Where is the sound comin' from? Engine area? Passenger dashboard area?
What happens if you manipulate the temp control (and nothin' else)???
Pro
Joined: May 2006
Posts: 637
Likes: 0
My bad about missing the hot air issue. And the code pull on the ac. It should be push and hold FAN up/down buttons for 5-6 sec. Then after you get -00 you push AUTO FAN and you will get codes.
00 no faults.
01 and 02 temp door motor circuit fault.
03 ambient sensor open.
04 -- -- short.
05 in-vehicle temp sensor open.
06 -- -- -- short.
07 solar load sensor open.
08 -- -- -- short.
09 low freon.
10 UART failure. (serial data communication between CCM, heater and the ac programmer (control head)).
00 no faults.
01 and 02 temp door motor circuit fault.
03 ambient sensor open.
04 -- -- short.
05 in-vehicle temp sensor open.
06 -- -- -- short.
07 solar load sensor open.
08 -- -- -- short.
09 low freon.
10 UART failure. (serial data communication between CCM, heater and the ac programmer (control head)).
Thread Starter
Intermediate
Joined: May 2008
Posts: 27
Likes: 0
From: Clearwater FL
My bad about missing the hot air issue. And the code pull on the ac. It should be push and hold FAN up/down buttons for 5-6 sec. Then after you get -00 you push AUTO FAN and you will get codes.
00 no faults.
01 and 02 temp door motor circuit fault.
03 ambient sensor open.
04 -- -- short.
05 in-vehicle temp sensor open.
06 -- -- -- short.
07 solar load sensor open.
08 -- -- -- short.
09 low freon.
10 UART failure. (serial data communication between CCM, heater and the ac programmer (control head)).
00 no faults.
01 and 02 temp door motor circuit fault.
03 ambient sensor open.
04 -- -- short.
05 in-vehicle temp sensor open.
06 -- -- -- short.
07 solar load sensor open.
08 -- -- -- short.
09 low freon.
10 UART failure. (serial data communication between CCM, heater and the ac programmer (control head)).
Pro
Joined: May 2006
Posts: 637
Likes: 0
Like Schrade says, My ´91 FSM says either:
Replace hvac programmer OR,
Replace heater case/temperature door assembly OR,
Replace temperature door motor.
There is a possibility that a temperature door isn´t aligned as it should according to my FSM, so you might get away without replacing stuff.
In either case it´s better for you guy´s to buy or borrow an FSM for your year. It´s 5-6 pages with diagnostics info to go through.
Replace hvac programmer OR,
Replace heater case/temperature door assembly OR,
Replace temperature door motor.
There is a possibility that a temperature door isn´t aligned as it should according to my FSM, so you might get away without replacing stuff.
In either case it´s better for you guy´s to buy or borrow an FSM for your year. It´s 5-6 pages with diagnostics info to go through.
