AC Compressor Problem

[MJBears99TJ]

Hello,

Hopefully someone can help. 99 TJ 4.0 AC compressor will not engage. AC has always worked. I tried to jump low & high pressure switch and compressor still will not come on, only way I can make it engage is straight wire it from the battery. I have replaced the HVAC controls in dash, and replace the relays in PDC box. anyone has any insight please let me know.

Thanks

 

[gdel]

Any luck with this? I’m having a similar issue

 

[CharlesHS]

Have you verified their is voltage going to the LP switch and AC controls?
You may need to go to the TJ Resources and download the Factory Service Manual PDF for your year TJ and search thru electrical schematics section 8W.

 

[gdel]

I jumped both the sensors and the rpms change but the clutch doesn’t engage. I checked the fuse and relay, both are good. The clutch moves freely if spun by hand and I can hear compression. Not sure if clutch or magnet are just bad.

 

[Shwiftypickle]

You need a power probe. Check each pin where the relay is. 87 pin is load 30 should be constant battery voltage 85 and 86 is control one power one ground. Something out of those 4 is missing.

 

[gdel]

i jumped 30 and 86 but it still didn’t engage. 30 had a 12v supply

 

[Shwiftypickle]

If you jumped 30 and 86 you may have cooked the pcm. Jump 30 to 87.

 

[gdel]

My bad, typo. I did jump 87 to 30. Clutch didn’t engage

 

[Shwiftypickle]

Open circuit in the power wire to the compressor

 

[gdel]

Any suggestions on how to test the electrical connection at the compressor? I want to check if it’s getting 12v. The quick connect is buried and not really accessible to test.

 

[Shwiftypickle]

If the wiring is good and there's not a break in it I'd go ahead and replace the compressor. The clutch is most likely open. Fairly common on older ac systems.

 

[John Scoggins]

Any suggestions on how to test the electrical connection at the compressor? I want to check if it’s getting 12v. The quick connect is buried and not really accessible to test.

Unplug the connector and see if 12V is getting to the plug, also check for ground continuity. Could be that the fly-back diode has not shorted and causing the 12volts not the reach the compressor clutch.

 

[MikeE024]

I jumped both the sensors and the rpms change but the clutch doesn’t engage. I checked the fuse and relay, both are good. The clutch moves freely if spun by hand and I can hear compression. Not sure if clutch or magnet are just bad.

I know this is old, but did you happen to verify the wiring to be good to/from the relay.

Also, did you happen to try a different relay to see if anything changed? I'm curious to know how you determined that your relay was good if you didn't try a different relay, and how you know your wiring was good. I ask because checking voltage does not always give you the information you need.