V8 Stingray

All of a sudden my A/C pump has stopped working. The alternator started dying a few weeks ago with voltage dropping and spiking - it has since been replaced, but noticed today that the A/C wasnt blowing cold air anymore and I couldnt hear the electomagetic clutch in the A/C pump kick in anymore.

I swapped out the fuse for a good one on the passenger side, but that didnt fix the problem.

What's the best way to troubleshoot this further? I dont have my voltage multimeter with me, but I do have a test light. Thinking I could pull the plug on the A/C pump and put the light on one of the connections to see if there is power going to the pump from the A/C panel.

What say you guys?

desertmike1

I think your on the right track! check for power and ground at the Clutch before going further.. is this a C3 or 4?

V8 Stingray

Checked for power - all good. Didnt check for ground, but will check that tomorrow. Its a 1986 C4. Clutch is not engaging at all.

Is there a pressure sender switch that controls the clutch? Or is it the control unit in the dash that controls it?

Just wondering how to test the clutch mechanism.

Hooked on Vettes

There were two AC systems.
C60 is manual AC.
C68 is auto climate control. Has a digital readout display.

If there is at least 47 psi of refrigerant in the system the low pressure cycling switch should be closed. If the switch is open you are low on refrigerant or the switch is bad. If you want to see the clutch engage, remove the plug going to the low pressure cycling switch and take a piece of wire and jump the two wires at the plug. Turn the ignition On and AC on. The clutch should engage.

The low pressure cycling switch and the hi pressure cut off are in series. The hi pressure switch should be closed unless the pressure is over 430 psi.

For the C60 system 12 volts from the manual control panel passes thru the hi pressure cutoff switch and the low pressure cycling switch to the clutch coil.

If you have the C68 and both switches are closed. Turn the ignition ON (no need to start the engine) and turn the AC on. The compressor clutch should engage. (Click sound).

If the clutch doesn't engage look on top of the evaporator housing. You will see two electrical connectors. One of them has a Black wire which is ground and a Dark Green/Yellow wire. When AC is requested the Dark Green/Yellow wire should measure around 6 volts DC. With AC off should measure zero volts. If it does measure 6 volts and the clutch doesn't engage, the Blower Control Module is probably bad. You can manually energize the clutch by grounding the Dark Green wire at the other connector plug on top of the evaporator housing. That simulates the Blower Control Module grounding the clutch coil.

The two electrical connectors are part of the Blower Control Module. You remove it by removing a couple of small bolts and it pulls out of the evaporator housing.

1 st two schematics is for the C60 system




Schematic for the C68 system



Diagram showing the location of the switches. For the hi pressure cut out switch identify it by the color of the wires at the plug. You will notice it's right next to the hi pressure fan switch. The switches can be installed in either position so go by the color of the wires going each switch.



Picture of the Blower Control Module

V8 Stingray

Thanks for the reply, a huge amount of great info there!

Just to clarify on this point: "If you want to see the clutch engage, remove the plug going to the low pressure cycling switch and take a piece of wire and jump the two wires at the plug. Turn the ignition On and AC on. The clutch should engage."

Which is the low pressure cycling switch that I need to jump in order to see the clutch engage?

I have the C68 system.

thanks!

Rowan.

Hooked on Vettes

In the picture diagram it says pressure cycling switch and connector.
It's a large two wire plug about the size of a mushroom.
You unplug the connector and jump the two wires together.
It's near the top of the evaporator box.