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1989 C68 HVAC No heat no A/C

 
Old 05-07-2015, 04:46 PM
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dspayne
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Default 1989 C68 HVAC No heat no A/C

the electronic control unit appears to be working. It lights up, I can control the blower manually (it does flicker when I hold the button down) it shows outside air temp and desired temp, checked for codes and none present. the blower comes on, the vent dampers don't move, no heat in winter, no A/C (compressor doesn't engage) I have the FSM but not sure where to start trouble shooting.

I did find a blown fuse for the A/C and replaced it. I do have vacuum (17in) at the ball and the ball does hold a vacuum. I have thought about just sending the head unit off to be rebuilt (since there is the flicker) but I don't want to do that with every part of the system. Since the head unit controls everything, I thought that may be a good place to start. Any suggestions on where to start would be appreciated.

Last edited by dspayne; 05-07-2015 at 04:54 PM.
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Old 05-08-2015, 01:00 AM
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Cliff Harris
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Originally Posted by dspayne View Post
I did find a blown fuse for the A/C and replaced it.
The A/C fuse is for the compressor only.

Originally Posted by dspayne View Post
Since the head unit controls everything, I thought that may be a good place to start.
Most of the A/C functions are performed by the HVAC programmer, which is attached to a bracket on the inside of the firewall above the gas pedal. Vacuum controls the movement of the HVAC air, so the first thing to check is that vacuum is getting to the HVAC programmer (black plastic tubing).

This article might be good background information:

https://www.corvetteforum.com/forums...schematic.html
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Old 05-08-2015, 06:53 AM
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Default checking the programmer.

Originally Posted by Cliff Harris View Post
The A/C fuse is for the compressor only.



Most of the A/C functions are performed by the HVAC programmer, which is attached to a bracket on the inside of the firewall above the gas pedal. Vacuum controls the movement of the HVAC air, so the first thing to check is that vacuum is getting to the HVAC programmer (black plastic tubing).

This article might be good background information:

https://www.corvetteforum.com/forums...schematic.html
Thank you, I will check out the programmer. I've been down there before and was hoping not to do that again. This time I'll go ahead and take some Aleve first.
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Old 05-08-2015, 10:05 PM
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dspayne
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Default voltage at clutch

I checked the voltage at the clutch, 3 volts and at blower control C1 and it also was 3 volts. At one of the pressure switches on ac line it was 12. Also the new fuse I put in for A/C blew.
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Old 05-08-2015, 11:34 PM
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Originally Posted by dspayne View Post
I checked the voltage at the clutch, 3 volts and at blower control C1 and it also was 3 volts. At one of the pressure switches on ac line it was 12. Also the new fuse I put in for A/C blew.
The engine does not have to be running to test the compressor clutch. I think it's much easier to test when everything is sitting still instead of spinning around and moving. A lot fewer incidents of jerk-your-hand-back because you accidentally touched something moving.

The voltage from the A/C fuse should be 12 volts. The compressor clutch is engaged by applying ground to the other wire. This diagram is for my '86 and I know there was a relay added a year or two later to control the compressor clutch, but this wiring diagram shows the general layout:


Last edited by Cliff Harris; 05-08-2015 at 11:43 PM.
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Old 07-11-2019, 08:46 AM
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SG Lou
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During this ordeal I have been corresponding with Paul Koerner as well. I sent him the same findings as I posted here and this was his response : Your voltages are acceptable, however, your command from the HVAC control head is not accurate. You will most likely need a control head
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