Question about 1999 Jeep Grand Cherokee

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A/C compressor turns on and off even though A/C is switched off

Jeep Cherokee 4.0 year 1999 A/C compressor clutch cuts in and shuts off about every 30 seconds even with the A/C switch in off position. When A/C ist turned ON everthing works fine.

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  • akobaer May 20, 2009

    Thank you. I will check the switches and PCM.


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Hello akaobaer...Sounds like you have a pressure switch defective or the system charge (freon) is low...The a/c clutch relay is operated by the Powertrain Control Module. However there are inputs from the low pressure switch (located on the accumulator) and a high pressure cut out switch (located on the discharge line near the compressor) that control whether or not the PCM turns on the clutch relay as well.
If the refrigerant level is low, the PCM low PSI switch will cause the clutch to cycle.
The PCM turns on the relay by grounding the negative side of the relay coil...The low PSI switch should turn on (close) at approx 34 PSI.....and will turn off (open) at 20-22 PSI...May sound complicated but it's really not. Have a qualified HVAC tech. check the system for leaks before recharging it, if needed.
Good luck...i hope this answers your question and will fixya up...

Posted on May 19, 2009

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Hi my name is leo and I have a 2002 jeep Cherokee Laredo a/c clutch will engage

Faulty low pressure switch , Google it to see how to replace, or you an unlucky it and run a jumper wire between the terminals/ But beware- bypassing the low pressure switch can ruin the compressor if it gets low on freon.

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I had auto shop put freon in and then they said was working fine...said pay and you can go, car cooling just fine...I go out to my car and complete system is dead. The fan controls in dash now dead....

If your system its empty of free on, yow wont be able to activate your ac compressor, you might have a leak some where, this its the simple answer, there could be more problems, a bad blower motor, relays, fuses, cloged system, etc.:)

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1 Answer

AC not running in my 1998 Jeep Cherokee. Changed AC clutch compressor RELAY, freon level is good, temperature sending unit replaced along with cooling fan! Checked all fuses still good. Can't seem to...

Hello, You have two switches which work off the pressure of the Freon. Both of these switches cut off the power to the compressor. One is for HIGH pressure and the other is for LOW pressure. Check for power at the compressor clutch connector harness while the controls are set and the engine is running. You may have power and a bad clutch.

When you say that the Freon pressure is good, does that mean the pressure is within the proper range? Too much Freon will make the HIGH switch cut off power and too little will make the LOW pressure switch cut off power.

The ideal amount(ozs) of Freon is what is recommended by the Manufactuer and it will provide a moderate amount of pressure of about 35psi-40psi. You can borrow pressure gauges, called Manifold gauges to measure your system at autoparts stores with loaner programs.

The low pressure side of the system is the one you use to induce the Freon to go into an empty system. You can bypass this switch by taking off the connector and putting a "U" shaped jumper into the harness and the compressor clutch should get power to LOCK up all of the time.

You can take off the switch connector at the compressor clutch and then check for power when bypassing the HIGH pressure switch if the LOW pressure switch does not make the system get power. Only, really only bypass the HIGH pressure switch with the clutch connector disconnected. The HIGH switch is there to prevent damage to all of the components from seals to lines to every piece of Freon hardware in the car. Bypassing with the A/C clutch disconnected will allow you to know if power is getting to the compressor clutch.

Finally, you can get FREE wiring and fusebox diagrams through Just sign and register to their site and then you can print the documents for yourself.

Good luck with this repair and I hope my solution helps you.

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The compressor clutch won't engage unless there is freon in the system. Connecting a gauge to the low pressure port should tell you if there is. Pressure in a system that isn't running varies with the outside temperature.

Apr 16, 2011 | 1999 Jeep Grand Cherokee

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The clutch on the ac compressor of my '96 Jeep grand cherokee engages for about 5-10 seconds then disengages for another 5-10 secs. Any idea on what causes this?

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A/C problem with 99 Jeep GC Laredo

If the compressor is running and the lines are getting cold that leaves the evaorator having a block, don't recall if that year has the orifice tube or not. In any case it is going to require opening the systems cleaning the lines and the oriffice then refilling the system. That means a vacuum pump and refriedgerant oil and the associated guages and freon. Live on the Gulf coast and you are right we do get hot down here!

Aug 31, 2009 | 1999 Jeep Grand Cherokee

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