5fingerfuller

Hey everyone, Ive resorted to my trusty friends here again. Youre all great. 99 xj, ac compressor wont kick in unless I run a jumper wire. Ive checked all fuses, replaced the relay. When I use the jumper wire, i hook my guage up to the low pressure side, and I have about 40psi so i know its not low. Where do i go next? i plug the connector back in and the compressor wont engage.

Saudade

What's the high pressure side read?

5fingerfuller

Im not sure. I just bought a bottle of refrigerant and read the pressure off the low side. I could run and get a gauge.

Saudade

Was the compressor running when you read the gauge (it takes a few minutes to stabilize)? What was the outside temp?

Best to get the manifold set so you can see what the high side is as well. Have you used one before?

5fingerfuller

Yeah the compressor was running, I let it run for a good while, the air temp in the garage was probably around 75. I’ve never done any more with the system, or any other system other than what I’ve mentioned above.

5-Speed

Could be the pressure sensor not reading. Bad news, if it is, you have to drain the system to replace it.

5fingerfuller

Is there a way to check that sensor?

5-Speed

I think if it works, it connects both sides of the sensor. Meaning, the factory wiring runs a ground into one side of the sensor and when the sensor sees enough pressure, it connects that ground to the other wire in the sensor, triggering the ac pumps clutch to kick on.

Rambler65

Unless it was removed at some point there should be a schrader valve under the low-pressure cutout switch/sensor enabling it to be changed without discharging the system. You can test the sensor with a multimeter. If working properly it will show continuity between the pins if there is about 20 psi or more in the low side of the AC system.

lawsoncl

I got burned by that assumption once on an old Mustang. The dealer installed A/C did not have a schrader under the low side sensor. The switch tested bad, so I started unscrewing it to change it, it spit the o-ring out after a few turns and wouldn't seal even retightening. Waited for it to finish dumped, and sure enough when I took the switch all the way out, no schrader or even place to install one.