Air conditioning

[GTP091]

Is there a way to test if the a/c circuit is ok?? the harness was bad so I replaced it but there is no voltage present when I test it with the AC turned on or off and the air doesn't work. I would imagine that there should be something so the clutch has power to engage??

[55trucker]

You'll need a minimum charge in the system to close the A/C low pressure switch, without that switch closed the system will not activate at all (you could bypass the switch with a jumper for test purposes), as well the circuit to the fans have to be closed (they do that automatically) as well before the A/C clutch will see voltage to engage.

[GTP091]

The system is pressurized so I'm sure the low pressure switch is fine. Any idea what else?

[55trucker]

Do you have any accurate way (such as a set of A/C gauges) to check the pressure in the system?...there has to be a minimum of 45lbs. pressure in the system for the low pressure switch to stay closed. As the system runs the high & low pressures are constantly changing, as the high side increases the low side decreases and when the low side drops to approx 35lbs. the switch will open and disengage the A/C clutch and the system pressure will equalize until the low side comes up to approx 45lbs. again and then close so the system can continue (this is the *cycling* of the compressor clutch you hear). The low & high pressure switches are mounted right on the back of the compressor. If you were to look at the back of the compressor as it is mounted on the engine the low pressure switch is the switch located closest to the engine block. The switches ground the two circuits they control to open & close them. The A/C clutch control relay hasn't failed has it?..It is located in the right side electrical center under the hood. As well, if the ECM is not *seeing* a request from the controls in the passenger compartment then the system will not engage, and lastly the power steering pressure switch circuit has to be working as well (this is controlled by the ECM) before the ECM will engage the A/C system. It's not the easiest of systems on the car to diagnose without the proper tools. Hope this info helps to some degree