The AC clutch on my Jeep Liberty 2006 won't engage. Here is what I have checked so far.

  • Fuse 14 in the passenger cabin

  • 21 in the engine compartment are ok

  • AC relay ok

When I jump the AC relay I am able to engage the compressor and get cold air, pressure at rest is about 105 pounds at 60 degree F. When the compressor is running it drops to 35 psi. I can't check the high pressure side because I don't have a gauge for it. If I jump the low pressure switch nothing happens. Not sure where to go from here.

Does anyone have an idea of what could be wrong?

What could be the root cause of this behavior?

  • does the car have auto or manual ac? if auto i'd lean towards a failed ambient air temp sensor first. if manual a failed control unit or pressure sensor. if you pull the relay check for power on pins 30 and 85 and ground on pin 86. 86 is the computer controlled ground for the relay. if pin 85 or 30 doesn't have power it may be the fuse or wiring to the fuse. it could also be a failed relay but you can easily check that by swapping it with another relay. the high pressure switch grounds when pressure is too high and the low pressure switch grounds when low side pressure is ok.
    – Ben
    May 22, 2016 at 13:42
  • pins 85 and 86 may be switched, one or the other is always hot or grounded key on and the other is computer controlled.
    – Ben
    May 22, 2016 at 13:53
  • Thanks for the imput. Both 87A and 30 show 12v. I swapped the relay and no change. This car has auto ac (you can set the temp so I guess its auto-manual is only off and on??) I have a ambient temperature led display in the head liner and the temperature on that is always correct, so unless there is a separate sensor for the ac, I am certain the temp sensor is ok. How do you check the high pressure switch?
    – mark b
    May 22, 2016 at 21:18
  • high side switch is normally open i believe, once pressure reaches a threshold it grounds the switch and the pcm stops grounding the relay coil. you could try unplugging the sensor im unsure if it would set a code or not though. this might disable the compressor clutch. you can also backprobe the sensor and check for continuity between the terminals.
    – Ben
    May 22, 2016 at 21:26
  • how do I backprobe the sensor?
    – mark b
    May 23, 2016 at 2:17

1 Answer 1


It may be a blown fuse. AC compressor clutches receive power in a number of ways. They can activate through a relay that’s energized directly by a proper condition of the low and high pressure switches. Or, the relay can be operated by the PCM which has interpreted the condition of the low and high pressure sensors.

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