The AC Compressor on my '94 Z-28 is not getting 12v power to the clutch pack. I measured this at the compressor plug with the engine running while the car was up on a lift.

I've tried swapping the AC relay with a known good one (horn), no change. However, I'm not sure exactly where I could put 12v to check out the wiring. AC pressure is around 0.3 v (changes slightly with temperature), as read out by my LT1 Scanmaster.

My head is about to just lock down. Help!

TIA, and have a good one,
Mike

 

It could be that the system is low on refrigerant R34. The system has a low pressure cut off swich and will not allow voltage to the compressor when system pressure is low to prevent damage occuring to the compressor.

 

No, that's what the 0.34v pressure reading is saying. It correlates to around 90 psi, which is a normal system pressure when the system is not running (i.e. both the high and low pressure sides have equal pressure).

Thanks anyway, and have a good one,
Mike

 

Unfortunately, you're going to have to hook it up to a scanner tyo see what's going on since there are a few things that can be going on. For example, you need to know if the computer is 'commanding' on the AC and if it thinks it's on. If it is commanding the AC on then check the ground wire on the relay...I believe that'll trace back to the PCM....

 

Other than a Scanmaster (which is installed), what kind of tool can I use for an old OBD-I system to watch that line?

Or, can you tell me which line coming out of the PCM is the AC command signal? I can put a DVM on that and see what's happening.

Thanks for the help, and have a good one,
Mike

 

AC request goes in the PCM on pin 1 on the black connector green/white wire.

Clutch drive is out pin 8 of the blue connector also on green/white wire. Look for DTC70

Clutch status is in pin 21 of the of the black connector on a green wire. Look for DTC69

pressure is in pin 12 of the blue connector on a red/black wire. Signal varies from 0 to 5 volts. Look for DTC 66 or 67

and temp is in pin 24 of the blue connector on the blue wire. Signal varies from 0 to 5 volts. Also DTC 66 or 67

The 5 volt reference for pressure and temp come out of the PCM on pin 29 of the black connector on the gray wire. Ground is on pin 16 of the black connector on the black wire.

 

Speedy,

That's awesome info; thanks for the detail.

None of those DTCs are present, but now I can start ringing out some lines and run through an elimination process.

It's going to be a few days before I get back to troubleshooting, but I'll let y'all know what comes out.

EDIT: One more question: Do I need to have the engine running, or is KOEO sufficient?

Thanks again, and have a good one,
Mike

 

If it's not in the correct state with KOEO then try it running.