MAN00XJ

Hi everyone! Im new here, and am glad to have joined the Jeep family.

I just bout a '00 Jeep Cherokee XJ, and I am having a small AC issue. It blows ice cold, but when it warms up, the cold air wants to cut out and blow hot, then cold whenver it decides to. I popped the hood, and found that the AC relay gets very hot..Im thinking the AC relay (which appears to be original) may be getting overheated and causing the AC to cut out. What do you think?

dangerousdavid

replace the relay and see what happens...they can't be that expensive

steve_k_37801

Did this ever fix your problem? I have 01 sport with same issue. But can't figure it out. I am thinking a bad switch but just not sure. Don't want to spend a ton of money.

johnfink

We went through a similar problem with my son's 2001 last summer. His complaint was that the a/c worked great until he pulled off the highway and slowed down. At that time it would start to blow ambient air. It would later begin to blow cold intermittently if he continued stop-and-go driving or would work completely normally if he got up to highway speeds. As the summer temps warmed up, he noticed that when he started the Jeep up after it had been sitting and was cold, the a/c would work fine. If he then just did slow-speed, stop-and-go driving, the a/c would work fine initially, but eventually would become intermittent. As usual, Dad got the call for a fix, although my son was many miles away at Fort Benning and had to do the troubleshooting for me. From my reading of the wiring diagrams for the 2000 and 2001 Cherokees, it appears that the electric radiator fan is not controlled by engine temps as in previous Cherokees, but only runs to cool the condenser/lower the high side pressure and maintain normal a/c functioning when the computer detects an a/c high side pressure rise. The way a/c works, high side pressure naturally rises whenever the Jeep slows down and stops pushing cool air through the condenser in front of the radiator. The electric radiator fan is supposed to turn on per computer command when a high side pressure rise is detected to provide cooling air flow through the condenser. If the electric fan does not run, the high side pressure rises to a level where the a/c is shut down by the computer until the system sheds the heat naturally and the pressure returns to a level where the a/c is allowed to function again. All of this is determined by a dual function pressure switch in the a/c high side line near the compressor sending signals to the computer. I asked my son if he ever heard the fan run, and he said no. We troubleshot the wires from the switches, the fan motor, the fan relay, and the wires from the computer to the high side dual function pressure switch and the low pressure switch. All checked out fine, so we tested and then decided to replace the dual function pressure switch on the high side line at the compressor. As I mentioned above, this is the switch that detects rising high side pressure and calls for the computer to turn on the electric radiator fan and also calls for the a/c to be shut down if the high side pressure becomes excessive. This switch has four wires into it, one or two of which are light green as I recall. That did it. The fan began to run normally and the a/c is perfect again. The switch was about $40 from AutoZone. I think this is the answer to several of the inquiries I have read on this forum regarding unreliable a/c in the last two model years of the Cherokee. I hope it helps you.

robertj

Great information John! It's not often that a person's first post on a forum is so informative.

MrJCRod

x2... from what I've read it's pretty accurate on the a/c side. the newer jeeps work on high side head pressures (the older jeeps fans came on as soon as the ac was turned on, provided the ac system worked) but I'm pretty sure that the fan is also controlled by temp... there have been quite a few days this summer that I've had it idling with the a/c system completely off and my fan would kick in when it seemed to hit around 220 on the temp gauge... I have a 2001.

johnfink

According to the manual I have read, in a 2000/2001 2.5L Cherokee, the electric radiator fan is considered primary and will run in response to high engine temps. My son's Jeep is a 4.0L, so I was concentrating on that system which I should have said earlier. That said, in the engine cooling description I have for the 4.0L Cherokee, it states,"Electric cooling fan 4.0L: With or without A/C request the electric fan will come on only when the coolant temperature is at least 106° C (223° F), and will remain on until the coolant temperature drops to 103° C (217° F) or below. Regardless of coolant temperature, When air conditioning system pressures reach 2068.5 +/- 138 kPa (300 +/- 20 psi) the electric fan will engage and continue to run until the A/C system pressure drops to 1620.3 kPa (235 psi) minimum, then the electric fan will shut off." So per this text, it is pretty clear that you are correct and the electric radiator fan has an engine temp response function just as it does for the 2.5L and previous model Cherokees. Nonetheless, as I worked through the wiring diagrams I could not find any connection between the temp sensor and the electric fan relay control circuit in the diagrams. They are both connected to the computer (PCM), but none of the diagrams showed any relationship between the condition of the temp sensor and a command to to the electric fan relay. I knew my son had driven the Jeep in lots of slow traffic in the heat of the Georgia summer and insisted he had never heard the fan run. When we jumpered the fan relay to test it, he heard the running fan loud and clear from the driver's seat so I thought he would have heard it previously if it had run due to engine temp. So, despite the text, without access to the Cherokee to test if the temp sensor will cause the fan to run I came to believe the wiring diagrams that show only the a/c dual function high side pressure switch as the enabler for the electric radiator fan. Thinking about this again, I know for sure that the a/c dual function pressure switch works as the manual states and per the electrical diagrams, but I cannot say for sure that the engine temp sensor does or does not cause it to run. If you have actual experience, I defer to you and agree that the engine temp can turn on the fan per the above text despite the lack of documentation in the wiring diagrams. Thanks for bringing this up. I hope this discussion leads to resolution of the a/c issues some of our forum-mates are experiencing. From my experience, it is not obvious that an intermittent a/c problem is really a failure in the control of an electric radiator fan, but it feels great when you get that a/c back working perfectly and didn't even have to break out the pressure guages!

MAN00XJ

Very good information John. Thanks for your response. I was thinking (after replacing the relay with no change) the problem may lie in the cycling switch itself. I appreciate your response, and will replace the aforementioned switch and let everyone know how that works for me.

johnfink

Glad to help. I became a lurker on this and other Cherokee forums after we found the 2001 2WD/4.0L/5-speed Cherokee last spring. It has a/c, cruise, and an aftermarket radio/CD. No rust, lightly used interior, and under accumulated dirt and stickers a lot of potential to become a fine ride. Our son was graduating from West Point and we convinced him it would be a perfect, hopefully-inexpensive-to-operate first car to get him to his training assignments before his first deployment this coming March or April. He paid less than $3K with 89K miles. My wife and I spent several days cleaning and polishing years of neglect off the exterior and interior surfaces. We replaced a few missing small parts, changed all the fluids and lubes, replaced the spark plugs and filters, repainted the wheels, and made sure everything worked as advertised. As you can see in the attached picture, it came out well and the smile on his face expresses his opinion of the vehicle when he finally got home to see it. The a/c switch has been the only emergent issue so far and is one of the very few subjects I feel sufficiently competent to provide advice on this learned forum. Thanks for the positive feedback and good luck with your project.
P.S. Just in case anyone notices, we had 4X2 decals made for the rear quarter panels just for fun since almost every other Cherokee out there sports the 4X4 decals and this one was not going to run in that league.

steve_k_37801

Was wondering if the switch could go by a different name. The reason I ask is that I went to advanced auto and they listed a switch on the accumulator which is not the one I need. Funny thing is all pressure switches listed are the same part number. Needless to say... Was wondering if someone has the part number for that switch. Frustrating!

steve_k_37801

Was wondering if the switch could go by a different name. The reason I ask is that I went to advanced auto and they listed a switch on the accumulator which is not the one I need. Funny thing is all pressure switches listed are the same part number. Needless to say... Was wondering if someone has the part number for that switch. Frustrating!

steve_k_37801

I was wondering if anyone had the part number for the cut out switch. The poor guys at advanced had any switches for the a/c listed as the same exact number. This switch is the one on the accumulator with the white band. It only had two connectors and not four. Or if it goes by a different name. Think I will try Autozone.

johnfink

Steve, this is what we replaced:

http://www.autozone.com/autozone/cat...&parentId=63-0

Autozone calls it a Cooling Fan Switch - Radiator, and it runs $38 when I entered my Virginia Zip Code. They show another switch as a high side pressure switch that I don't believe is even in this model Jeep. You are right that it is not on the accumulator, it is on the high side line near the compressor. Happy T-day.

steve_k_37801

Hello again. It has been a while since last post. Still having issues with a/c. I did replace the MT1199 switch with no luck. Any other ideas on this problem?

steve_k_37801

Hello again. It has been a while since last post. Still having issues with a/c. I did replace the MT1199 switch with no luck. Any other ideas on this problem?