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Ron, ASE Certified Technician
Category: Chevy
Satisfied Customers: 35305
Experience:  35 years experience with ASE Certs
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I have an issue with the C68 Climate Control System on a

Customer Question

I have an issue with the C68 Climate Control System on a 1992 Corvette. The control head seems to work with no problems, it reads the outside temperature correctly and all buttons work. The fan works, it starts out blowing in the defrost and heat position but then changes to the dash vents as well as speeds up with the manual controls on the unit. I get no change in temperature when the system is adjusted and the compressor will not engage. I have pulled the resistor in the box (under the hood) to view the blend door, the blend door constantly moves but will never completely close in either direction (this is with the temperature setting set at maximum or minimum). It will almost close for cold but only a little over half way for for warm then goes back to allow mostly cold air. It seems to want to oscillate near where it would need to be for cold air. There is a wine that is present for a short amount of time after starting, thios comes from under the hood more towards the drivers side, but it does not sound like what I am use to being a vacuum leak. When the blend door is moving there is a click but this seems to occur when the motor changes direction. I do not want to just throw parts at the repair because a few of them are really espensive. Any help would be appreciated. Thank you.
Submitted: 1 year ago.
Category: Chevy
Expert:  Ron replied 1 year ago.

Hello, my name is ***** ***** I am a professional here at Just Answer. I have noticed that your question was not getting a response and thought I would see if you still need help with this.I apologize for the delay and I hope I can still assist you with this here.

As long as the compressor is not coming on your not going to get any cold air, before you consider replacing any thing the first things you need to do is check to see if the AC system is full of Freon as well as checking both heater hoses at the firewall on a warmed up engine to see if both are getting hot indicating you have good flow through the heater core. Check these two things for me and post back with the results and we can work from there.

Customer: replied 1 year ago.
Ron, I finally had a chance to check the heater hoses on the car yesterday. First off, everything on this car is what came on it in 1992. The hose from the throttle body to the heater control valve does get hot and the hose from the heater control valve to the heater core gets hot. The only difference in these two is pressure before and after the heater control valve. The hose from the heater core to the radiator tank at the firewall also gets hot. During the check, with the temperature set at 90 degrees, there was a very slight amount of warm air coming out of the floor vents and only cold air coming out of the defroster vents. (During the test these were the only vents that would work.) The fan was operated with the manual switch during the test and was not set to auto. I did not get a chance to check the Freon.
Expert:  Ron replied 1 year ago.

If the system is full of coolant and the thermostat is working properly the hoses should be to hot to hold on to, 90 degrees is on the cool side. If you think the hoses are hot enough at the firewall then the problem may be under the dash with one of the blend doors. Before you do anything else, lets try a reset on the control panel, to do this disconnect the negative battery cable for a few minutes and then recheck the AC/heater operation.

Customer: replied 1 year ago.
Ron, the 90 degree setting was the highest the control unit would let us set it. The heater hoses were much hotter. The battery has been disconnected on the automobile, the most recent time was Saturday. The system does the same thing each time the battery is reconnected. Once reattached, with the car running, the green light over the button that is active will blink for a short period. If you hold the up and down arrow on the control unit until "00" is displayed it will eventually cycle through a code readout on the dispay is 01 and 02. No other codes are ever shown.
Expert:  Ron replied 1 year ago.

Try running the self test once again for me and do it with these steps. Press the "fan up" and "fan down" buttons at the same time. "00" will appear. Press "auto fan" and check for trouble codes

Customer: replied 1 year ago.
Ron, the trouble code that is displayed at this time is "01". Today I am not getting the" 02" code but the vents are controllable . As I said only the "01" code today.
Expert:  Ron replied 1 year ago.

If the vents are controllable and the heater hoses and core are getting hot then you really should have heat. Are you sure the heater core is getting hot?

Customer: replied 1 year ago.
The heater core is heating up.
Expert:  Ron replied 1 year ago.

Okay then you back to some sort of control issue , if the core is hot and the controller is controlling air flow the heater should be getting hot.

Customer: replied 1 year ago.
That gets to the expensive parts I originally mentioned. I do not want to just replace expensive parts unnecessarily. Is there any way to test these parts and not just "throw money" at it?
Expert:  Ron replied 1 year ago.

From everything we have already checked it sounds like it should be working, you say the controller works with proper air flow and the heater core is getting hot. At this point I am out of ideas. If you would like me to open the post back up to see if someone else has something different to offer I can do so. Let me know.