No power to compressor

[Gary Willard]

Please help me analyze this.... My car was taken off the computer before i bought it and is still running on the original block and transmission after mods made. The AC has never worked and now i want it to. Ive done the system conversion to R134a. Flushed condensor & evaporator, replaced accumulator and low pressure switch, new orings, vaccuum check and tried to charge the system with gauges. I have good fuse and contnuity at the switch. Clutch will engage with direct voltage, but it is not getting voltage from the pressure switch side. What could my problem be? A switch bypass does nothing, so i have an issue between switch connection and the compressor. Did removing the computer cause an issue I don’t know about?

 

[81Regal]

Are you getting power to the pressure switch? Also IIRC the power goes through the 4 pin connector by the passenger side valve cover, that connector commonly melts.

 

[Gary Willard]

I am not a big electrical person, but do understand the very basics. With the ignition off and the 2 wire Pressure switch harness disconnected, i checked the harness for continuity and it had none. I also checked it for voltage and there was none. Then i started the car, turned on the AC and checked the harness again for both, and still nothing. That’s what made me think I’ve got a problem somewhere in this part of the system. I also jumpered the disconnected harness while running and with the AC turned on and checked for voltage at the clutch, but still nothing. I thought the pressure switch only acted as a contact for closing or opening the circuit of power heading to the clutch. If it is supposed to have voltage at the pressure switch harness, how would i check it? You mentioned a four pin connector down by the passenger side valve cover. There is a single ground wire connected to the valve cover, but there is also a female end of a connector in the same group of wires. However, i don’t see the male end of the connector anywhere. Could this be my problem?

 

[pontiacgp]

if all the other selections work have you checked for power coming from the control switch

 

[Gary Willard]

Thanks for the diagram! This will hopefully allow my limited electrical skills to easily find my power issue! I’ll post my findings as soon as i get it figured out.

 

[81Regal]

You mentioned a four pin connector down by the passenger side valve cover. There is a single ground wire connected to the valve cover, but there is also a female end of a connector in the same group of wires. However, i don’t see the male end of the connector anywhere. Could this be my problem?

There should be a ground wire to the back of the cylinder head. If you only see one half of the connector that could very well be the problem. The 4 pin connector has a large red wire that feeds power to the blower motor relay. Ill try to get a picture of what the connector should look like.

 

[pontiacgp]

There should be a ground wire to the back of the cylinder head. If you only see one half of the connector that could very well be the problem. The 4 pin connector has a large red wire that feeds power to the blower motor relay. Ill try to get a picture of what the connector should look like.

the lack of a ground would interfere the compressor's operation but the op said he has no power on the feed line

 

[L92 OLDS]

Thanks for the diagram! This will hopefully allow my limited electrical skills to easily find my power issue! I’ll post my findings as soon as i get it figured out.

If you are working on your 84' Hurst Olds the schematic will be different than the one shown above. The H/O's have a special AC compressor cut out switch (unique to early VIN 9 cars) on the accelerator pedal. When you give it WOT the switch opens the circuit for the compressor clutch. You might want to check for voltage there and for correct switch adjustment.

 

[81Regal]

I was talking about the engine to body ground. True the OP was talking about no power to the compressor but that wire also goes through the same connector.
It does help to know what car the OP is working on.

 

[L92 OLDS]

There is a single ground wire connected to the valve cover, but there is also a female end of a connector in the same group of wires. However, i don’t see the male end of the connector anywhere. Could this be my problem?

What color wires are coming out of the pressure switch? IIRC, the compressor ground is interrupted by the pressure switch on newer G bodies.