RVTECH

Just purchased a 1991 Corvette Base Automatic.


The AC Relay mounted just under the gauge cluster to the left of the steering column has the dark green wire cut. The dark green wire going into the relay is currently wired to a toggle switch and then to ground. This toggle switch turns on the AC Clutch/Compressor and one cooling fan. If I turn this switch off it will turn off the AC Compressor, but not the cooling fan until the engine is turned off.
When I want to use the AC I turn it on via the AC/Heater Controls on the dash above the radio and then flip the toggle switch to provide ground to the AC Relay. This turns on the Compressor and one Cooling fan.


I would like to fix this properly and remove the added toggle switch and reconnect the dark green wire as stock.
The relay has two brown wires, one light green wire, and the cut dark green wire.


The wiring diagram I have looked at shows that cut ground wire as going to the ECM, but I also see a dark green wire going into the AC Control operation panel above the radio.


Can anybody offer any help or advice for me to track down the correct repair for this Relay Ground so I can remove the rigged ground toggle switch from the previous owner?

WVZR-1

Does this car have C68 (automatic) AC or C60 (manual) control AC? It would seem that likely the AC request from the AC control is always "active" to the ECM and the toggle is used to "interrupt" the signal to the relay. The type of AC might make a difference but it appears the wiring diagram you've seen is correct. That starts the fan by default and once the fan is running then the balance of the fan control electronics takes over. A pair of tan wires yes with lt green and the dk green you've ID'd as going to the ECM.

RVTECH

It has the electronic (LCD)automatic HVAC control panel. Not the manual control.
HVAC control model 16150511.

WVZR-1

I would say then that there's likely a problem with the "programmer" that originates the AC signal to the ECM and the toggle corrects that. I have never had a C68 programmer issue but there are some interesting threads regarding them.

In the wiring diagrams that you have do you have the compressor command for the C68 (LED/auto) that includes the programmer? But you also have to consider that the AC control does the signal to the "programmer" to start the entire process. The diagnostics could get quite drawn out.

The diagnostic tree for the compressor control isn't that difficult it seems. Without the toggle and the wire connected/repaired "wire to wire" will the COMPRESSOR CLUTCH NOT ENGAGE or is the COMPRESSOR CLUTCH ALWAYS ENGAGD?

How about a wire repair and a new relay?

RVTECH

I had tested the relay and it was good.
I just finished taking apart and cleaning the circuit board and connections inside the HVAC Control Panel.
I reinstalled the cleaned control panel, removed the toggle switch and reconnected the dark green wire as stock without the added toggle ground.
Everything on the AC worked perfect.
I did not try removing the toggle ground before I cleaned the AC control panel so I do not know if that was the problem. The previous owner said he added that ground for the Compressor to work.


The cooling fan stays on when I turn the AC off, but the AC turns off. Is this normal or does it just run for a certain time period?


Hopefully that solved it or it will be something intermittent.
I will not drive it again until next week because I have the Gauges removed so that I can replace the LCD Polarizing Film and just ordered that today.


I will update next week on if it is good or starts acting up.


Thank you for the replies. - Ron

WVZR-1

I believe the cooling fan continuing to run is correct. With no AC the secondary fan (if that's the one you're mentioning) should turn on @235 and off @226, primary fan on @226 and off @221. There are ECM faults that turn on the fans by default.

Fan 1 (left), Fan 2 (right)

Sounds as if you've done well!!

RVTECH

Thank you!