Yes, another overheat thread

[Dragon158]

Ok, I know... but I haven't been able to find the info I'm looking for, what I'm looking for is an explanation of how my system works. I'm new to Cherokees and this is the first time I'm seeing this dual pressure cut off switch mounted to the line on my 2000. I understand that this setup was only used on 2000 & 2001 models.
First a little history, I had a small overheating issue last summer. Thermostat was shot, replaced and all was cool. Then the a/c compressor locked, or just about locked up. I swapped a new one, all was cool again. Towards the end of last summer I saw a puff of steam and traced it to a small pin hole in my radiator. Swapped in a new one, all was cool once again. This fall I noticed my reservoir was empty and found a leak at the weep hole on the water pump, swapped a new one and I was cool, again. Well this passed friday I was in heavy stop and go city traffic, with the a/c cranked and the temp around 90 degrees. I hear the chime and see the warning light to check gauges. The temp was up to 230 / 235. I pull over, pop the hood and see the electric fan is out. I continue driving home, with a/c off and had no more overheat issue. When I get home I start diagnosing the issue, jump the fan, check the fuses... then I see this switch. I google a bit and find somewhere someone says to ground the switch, if the fan works when grounding it's a bad switch. I order the switch from the dealer, install it today and still no worky. I have access to Chrysler and started digging through wiring diagrams and want to see how this system works, since throwing money at it doesn't seem to work. I find a diagram that says the pcm supplies ground to the circuit to turn the fan on & my pcm doesn't appear to be doing that, I ran a jumper to ground and the fan worked. So now I'm looking at an expensive pcm. Now onto what may turn into a bunch questions, where does the temp side of the system come in? Obviously that isn't working either. As far as I can tell the electric fan doesn't work with the a/c on or the temp going to overheat. I have access, but can't navigate Chrysler very well & find diagrams for circuits is a bear, probably because I'm still used to books. So in closing if anyone has any idea how this system works, or has been down this road PLEASE chime in. Like I said, this system is new to me & I can't throw a $500.00 PCM at it. But I may throw a toggle switch at it...

Thanks in advance, sorry it's sooo long. - Shawn

[abebehrmann]

From what I understand the fan is supposed to come on if the ac is on and/or if the temp goes above 219. If the fan works when jumpin it, my best guess would be a fuse or relay. I think the temp switch you mentioned actuates a relay which turns on the fan. Sorry, this probably doesn't help you much. I'm sure someone more knowledgeable will be along shortly to answer your question.

[Dragon158]

No, thanks for the reply. I did find where the fan works with or with out a/c engaged. All the fuses were good... I couldn't see how the temp circuit was wired. I know the low pressure and dual pressure a/c switches are in series & if one is out... nothing works.

[XJ Wheeler]

I would try the relay. Its probably the more common issue. Try replacing it with one of the others that fits and see if it works.

Sent via messenger pigeon - i talk, he types.

[XJ Wheeler]

Abe is correct about its function. When the a/c compressor is turned on, by either the a/c or defrost the fan is suppose to cut on as well to help cool due to the extra load on the engine. Also, once the temperature reaches 218-220°f (sources have noted either) the fan turns on and back off at 205°f.

Sent via messenger pigeon - i talk, he types.

[Carves]

Just had a look what is s'posed to be a 2001 manual ...


Glad I have 97/98 .. :D


You said you checked "fuses" ... just the ones under the hood - or the ones in the kick panel as well .. ?? ... as the manual says theres a fuse for the relay in the kick panel.

I could well be wrong ... but I doubt its a PCM fault. That ground path you read about is activated by inputs TO the PCM by the various sensors.

... Much more likely to be a fuse / relay / sensor / wiring issue, IMHO.

[Dragon158]

Yeah, relay was swapped & you can hear it click when you plug it in. All fuses were checked, there is a big Maxi 40 amp under the hood & a 15 amp at the kick panel. The way I read the "manual" was the pcm supplies ground to the circuit, which I think it's supposed to... because I traced that wire to the pcm. I think it's blue with a pink tracer... I take that with and jump it to ground and the fan worked. I submitted a trouble ticket to Chrysler through a friend, he gave them all the info and says they get back pretty quickly with responses. I guess all in all it's a good system, not many responses so far, so I assume there haven't been too many issues. Lucky me! Thanks for the suggestions and let me know if I missed something...

[Carves]

Yeah, relay was swapped & you can hear it click when you plug it in. All fuses were checked, there is a big Maxi 40 amp under the hood & a 15 amp at the kick panel.

:thumbsup:



The way I read the "manual" was the pcm supplies ground to the circuit, which I think it's supposed to... because I traced that wire to the pcm. I think it's blue with a pink tracer... I take that with and jump it to ground and the fan worked.


Yep ... Blue/Pink trace.

Ive had a toggle switch to ground, on mine in the past ... be warned tho - post 97/98 models - can display a fault code if you set it up that way.

Theres a thread on .... sorry Mr Mudderoy ;);):o:D ... jeepforum .... with about a gazillion posts on fitting a bypass.

.... personally, I still think your issue/fault - will lie with something, that "tells" the PCM to activate the ground path.

[4.3LXJ]

Just for giggles, try disconnecting the battery cables and touching them together. This will reset the ECM and maybe, I say maybe, this will cause it to use hard wired memory

[Dragon158]

Well, I got word from Chrysler that my pcm is shot, I listed all the tests I did in the ticket and explained how I grounded that blue/pink wire and they say pcm is the problem. As far as I know I didn't get a code by jumping the fan to ground, but I already have an evap code, so I need to scan and see... I'll end throwing a toggle switch in and see about locating a junkyard pcm, maybe. I'll try touching those cables too, never heard of that though.

[Dragon158]

Turns out the PCM is good, The dual switch was bad after all. The fan kicked on, at high a/c pressure on the ride to the beach on Friday. I guess I just couldn't get the pressure and temp up in the shop. Oh well, at least it's cool now!