Air compressor not engaging
Thread Starter
Seasoned Member
Joined: Dec 2009
Posts: 429
Likes: 0
From: Wichita, KS
Year: 1999
Model: Cherokee
Engine: 4.0l I6
I have checked the fuses ran the jeep with the switches on and off. I can never tell if the compressor is turning on or off so I can only assume it is not turning on. I did check the refill point and it reads 100 but The compressor is not kicking on so I cant get an accurate measurement. Ideas of what to do next?
Senior Member
Joined: Mar 2013
Posts: 691
Likes: 2
From: Texas
Year: 1993
Model: Cherokee
Engine: 4.0L
What exactly is your problem? A/C in your '99 is not blowing cold air and you are trying to charge it with a 134a kit from the parts store? Has the A/C been working in the past but losing refrigerant?
What is "refill point" of 100? If this is an indication of charge status, you are correct in that it is meaningless w/o compressor running.
What is "refill point" of 100? If this is an indication of charge status, you are correct in that it is meaningless w/o compressor running.
My guess would be one of those AC pro can with the gauge. One thing with AC you can't just "top it off" so to speak you need evacuate the air out of the system and draw a vacuum in order to fully charge a AC system correctly
Yes I have done it but just "topping it off" but I also have a full gauge set to read, high and low pressures it can be done but its not really recommended.
Have you jumped your pressure switch to fool the compressor as if it has enough pressure. If jumping it helps then you might not have enough freon but it sounds like you have air in the system and is causing you this problem.
Yes I have done it but just "topping it off" but I also have a full gauge set to read, high and low pressures it can be done but its not really recommended.
Have you jumped your pressure switch to fool the compressor as if it has enough pressure. If jumping it helps then you might not have enough freon but it sounds like you have air in the system and is causing you this problem.
CF Veteran
Joined: Aug 2010
Posts: 8,357
Likes: 103
From: Canton, MI
Year: 1999
Model: Cherokee
Engine: 4.0
Here's how to fool the AC system into engaging the compressor:
Hook up your refill bottle setup to the AC low pressure servicing port (Charge Port).
Remove the connector from the Low Pressure Cycling Switch on top of the Accumulator and jumper the pin cavities in the connector using a small paperclip. See pic.
Set the climate control mode selector to an AC setting, start the engine, the compressor should engage and the Radiator Electric Fan should run.
Monitor the refill bottle gauge for pressure. You're reading the low pressure side of the Freon system. Fill as required. Caution: If the pressure reads zero you should not run the compressor but for a few seconds without refilling to prevent the compressor running without lube.

Temp/Pressure chart:
Hook up your refill bottle setup to the AC low pressure servicing port (Charge Port).
Remove the connector from the Low Pressure Cycling Switch on top of the Accumulator and jumper the pin cavities in the connector using a small paperclip. See pic.
Set the climate control mode selector to an AC setting, start the engine, the compressor should engage and the Radiator Electric Fan should run.
Monitor the refill bottle gauge for pressure. You're reading the low pressure side of the Freon system. Fill as required. Caution: If the pressure reads zero you should not run the compressor but for a few seconds without refilling to prevent the compressor running without lube.

Temp/Pressure chart:
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