Weird A/C Electrical Issue

[rocktoy]

OK everyone need some help. I have a 1995 Explorer and am having electrical issues with the A/C. When I switch the A/C on the compressor will not come on and the WOT relay cycles causing the motor to rev up and down slightly. I have checked for 12v at the WOT relay and have it but if I try and jumper the connection the compressor will not come on. If I apply power to the compressor the clutch will engage. While checking power at the high pressure cutoff power is cycling with the WOT and engine. I have tried a replacement computer but that did not help. I am thinking of of the engine sensors is giving a bad signal causing the A/C to not come on. Anyone have any ideas?

Thanks,
John

 

[Dilbert5]

Are you positive that the WOT relay is cycling? The ac fuse, (in the central junction box), supplies power to the WOT relay, which then goes directly to the compressor clutch. So if you have 12 volts at the relay, and you can hear the relay cycling, and the compressor clutch is not engaging. It means that either the relay is bad, or the wiring is bad. Have you tried swapping relays, I believe the fuel pump uses the same relay (not sure because the wife has the car at the moment, I cannot check it).

If you swap the relays and the car doesn't run, you will know for sure that the relay is bad.

 

[rocktoy]

Dilbert,

I did not swap relays but did check it with a volt/ohm meter and it checked good. The 12 volts comming from the A/C panel is there but when I jumper the relay it still will not power the compressor. Something is restricting the power. My power probe shows power there but it is obviously not enough to power the compressor. I am at a complete loss. The system worked fin and then nothing. I did have a problem sometime ago with no cool air but found the vacuum line under the glovebox disconnected which allowed the hat water valve to stay open. After I fixed that the air was great now this.

 

[Dilbert5]

Get a pin probe, one that is thin enough to backprobe connectors. You need to slide the probe into the rear of the connectors so that you can measure the voltage while everything is still hooked up.
It sound like you have high resistance somewhere, and unless you measure voltages with a load present, you will not see the drop (DVM's have far too high of input impedance, so you must have the normal circuit load present).

 

[rocktoy]

Dilbert,

OK will try might take a few days due to time constraints. Another bit of info is while the system was all hooked up I did back probe the high pressure switch with my power probe and power was cycling there at circuit 198/t-y wire. Thanks for the info will let you know what I find.

John