So I drove the daughters 2000 Jeep Cherokee Sport 4.0 to work this morning for it's maiden voyage after replacing the head, headliner, shocks and a multitude of other repairs, and the A/C quit working halfway there, I have a 45 minute drive. When I got to work the compressor wouldn't even come on or so it appeared. When I left work the compressor came on, I didn't run it cause I knew there was an issue so I sweated 60 minutes in traffic home. Did some checking and my pressures are fine, I had thought I blew a hose, the low side cycles down to 20 and goes as high as system pressure, maybe 120, the high side is a little higher than I like when running at 250 psi but I think that could be a restriction in the orifice, or just the temp, it was 100 degrees today, There could be a restriction in the orifice, it is a 2000 after all, but it's not a charge issue.

In troubleshooting, I noticed that my compressor gap is most likely to large, I can see the clutch trying to pull in but it doesn't go, I can kick it in with a screwdriver, carefully, but the coil won't pull it in when it gets warmed up. I know how to fix that but it doesn't look easy to measure the gap with the clutch recessed into the pulley like it is.

The other thing I noticed is the e-fan isn't coming on when the A/C is on. This is a 2000 and I believe they changed from 2 sensors and went to one water temp sensor at the thermostat housing, is this what I'm looking for? I believe the relay is in the engine load center so I know where that is. The wiring is all original so that shouldn't be an issue. Anything I'm missing or need to consider?

Thanks in advance for advice.

Here's a description of your AC switch functions and the switch positions under various system pressures.



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Low side pressure seems a little low. Start the jeep and run it until the AC stops again, then without turning the jeep back probe the connector at the compressor and see if you have power with the AC on. if you have power going to the compressor then it's likely you have a failed compressor. If you dont have power going to the compressor then I would start checking the pressure switch as mentioned above

Low side pressure seems a little low. Start the jeep and run it until the AC stops again, then without turning the jeep back probe the connector at the compressor and see if you have power with the AC on. if you have power going to the compressor then it's likely you have a failed compressor. If you dont have power going to the compressor then I would start checking the pressure switch as mentioned above

In my 2001, I had to shim the clutch around 2007-2008. A few years later I replaced the whole compressor and clutch assembly. The tests and information above is solid information. Around 2000 the A/C system was changed so the aux fan only comes on with the right pressures & coolant temperature; it no longer comes on anytime the clutch is activated as in previous years.

Excellent info CCKen, exactly what I was looking for. The compressor is working so that is not the issue, pressures could be but not for the e-fan. From what I understand, the E-fan should be on whenever the compressor is on. I needed to know how the E-fan was wired and what controlled it. My clutch had one shim on it and it's not thick enough to make that much of a difference. The spring plate is pretty worn, if I can't find a better one in the junkyard i'll have to go with a new clutch assembly to repair the clutch.

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Are you saying the compressor engages when you select AC on the mode selector...If so that should mean the discharge pressure is below 270-330 psi and the Suction pressure is above 34-38 psi. Under these conditions (pressures) the fan should be operating.


Note that the dual function high pressure switch contacts 2-4 control the fan. This switch could be functioning (engaging the clutch) but the fan contacts (2-4) are not working. Or the switch contacts are working and the PCM is receiving the Fan Request but not turning the fan on.


When the PCM receives the fan request it provides a ground to the fan relay control coil, pulling in the power contacts of the relay to power the fan.


The PCM will use this fan relay control coil ground driver to activate the fan relay whenever the coolant temperature exceeds a set value in the PCM. The Engine Coolant Temperature (ECT) sensor on the thermostat housing provides the PCM with the over temp signal.


A simple test can be conducted to see if the fan circuit is intact, i.e., fuses, relay, fan, PCM ground driver, and wiring, by removing the electrical connector from the ECT sensor then starting the engine. If the fan circuit is intact the fan should run. If it doesn't a component in the fan circuit is defective.


Doing this test will trigger a check engine graphic on the instrument cluster because a P0118 DTC has been set. Use a code reader or scanner to clear the code, or remove the battery NEG post connector for about five minutes then reconnect.


Do this test and get back.

Yes, the compressor operates normally when the A/C selector is engaged. The clutch won't pull in after it warms up because the spring plate is worn and I either need a new spring plate or clutch, but it will still operate well enough for troubleshooting the fan.

One of the earlier posts mentioned that a change was made in 2000 where the fan doesn't operate anymore whenever the A/C is on which I wasn't expecting. If that's the case, then the fan may actually be operating correctly, it just didn't meet the conditions to run while I was working on it.

I will run your test tonight and post results, thanks for the excellent information.

Tested tonight, pulled the ECT sensor plug and within 5 seconds the E-fan came on and operated well, had the check engine light as expected. Based on that, it appears the E-fan circuit was always working just not as I expected. I expected it to be on whenever the compressor was on. So looks like if I fix the clutch and adjust the pressures I should be good to go. Based on your pressure limits, I may be a little low.

Thanks again for the fantastic info and help, I really appreciate it. I'm one step closer to getting this to my daughter who is patiently waiting as I work through the issues with it.

JMO
If the clutch is gone (really difficult to locate separately) the compressor itself can't be far behind, time for an A/C system rebuild.

Here's the pressure temp chart to go by when checking/adjusting refrigerant:



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Did you ever resolve this? I have the same symptoms, but I only have the guage that comes with the $39 refill to go on. The pressure goes into acceptable range for ambient temp then drops to around 20 then back up, then back down.

Take off clutch and clean with a wire wheel.
Mine worked great after that!
I also removed a shim on mine; may or may not be necessary.

Your issue sounds like a low charge possibly
is the compressor off when you see the pressure rise?