OffRoadNewb

Alright, summer time is nearing, and I haven't had the ac working since last fall, the compressor would not turn on at all, although it seemed to have the correct level of refrigerant in the system.

SO I took it in to a mechanic to diagnose. He said that the refrigerant was low, but even though it was low that the electric fan for the AC should still come on when I choose AC in the cab. So I paid him $85/hr (1hr) to diagnose why it wasn't telling the AC to turn on (the fan/whole system). He told me that the temperature control unit was bad and needed to be replaced. Quoted me $450 to replace it with a used one. I decided not to and do some research first.

Before I buy a used temperature control unit online for ~$40, it seems to me that if the refrigerant in low, that the low pressure switch would tell the PCM and it would not let the ac system turn on, and the electric ac fan would not run. Am I correct on this? If so, how did this guy diagnose my temperature control unit as being bad without having the proper level of refrigerant for the system to even run?

Trying to get this fixed before the "winter" in FL is over... any help is appreciated. I am pretty mechanically inclined, but electric and AC systems evade me for the most part. 2000 XJ Sport with manual temperature control.

djb383

The blower/fan should run in any of the 7 vent selector positions, compressor engaged or not. The manual temp control, to the right of the vent selector, has nothing to do with the blower/fan.

drhoward1988

I think he is referring to the condenser/aux. fan. It should run if your coolant temp gets above 210*F IIRC. It won't come on in AC though if your refrigerant is low, as it's on the same circuit as the compressor clutch.

djb383

U mean the radiator efan?

drhoward1988

Ya. I'm not sure of the technical name as I've seen it called several different things. I just know on my renix that's how it operates. Not 100% sure on newer ones. Hell that's the only logical thing I think he could be talking about lol

djb383

On '00/'01 XJs, the radiator efan does not turn on the moment the compressor engages. '99 down do, but not '00/'01. On '00/'01 XJs, the radiator efan turns on when refrigerant pressure reaches X PSI or coolant temp reaches 223F.

drhoward1988

Ok sorry for the missinformation. Wasn't aware of that on the newer ones.

OffRoadNewb

Yes, I was referring to the efan on the radiator. All other functions work on the temperature controls (heat, blower speeds, and vent locations). So basically I got charged $85 for this guy to tell me my manual temperature control unit is bad... when it's probably not?... ugh

CCKen

Open this link and scroll down to post #42 for data pertaining to '00-'01 AC switching.

https://www.cherokeeforum.com/f2/gre...e-6558/index3/

OffRoadNewb

That was some very helpful information, and confirms my thoughts that it could not be diagnosed without the refrigerant and pressures being at the correct levels. Thank you.

I have called and talked to the owner of the shop who I delt with before and he has welcomed me back to have his ac guy run me through his diag process on my XJ while I'm there for no charge. Guess I will do that next week on my day off.

I removed, dis-assembled and inspected the temperature control unit last night and couldn't visually see any faults. It's a very simple design and function, making it harder for me to belive that it's faulty.

OffRoadNewb

Unless there was some way to trick or bypass the pressure switch...

drhoward1988

Easy. Jump the two wires together... but this could result in compressor damage. The refrigerant carries oils through the system for lubrication.

OffRoadNewb

Great... so even if they did jump it to get the compressor to run I have to worry it being bad now too.

If they did, that would have rulled out the temperature controller as it needs to be on the correct setting for it to run regardless if they jump the switch correct?

djb383

Your mechanic is both correct and incorect.........

Radiator efan should turn on, a/c compressor engaged or not.....that part your mechanic is correct on.

U say everything works correctly regarding the dash HVAC controls.....that part your mechanic is incorrect on.

OffRoadNewb

Damn it... so the electric radiotor fan does not turn on and should even though the compressor may not... So what do I need to be doing or looking at myself? Like I said, electrical and ac stuff is my weakness. I have very little to no time on either then the basics.