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AC/ Electric fan woes

Drewlee77

NAXJA Forum User
Location
Abilene, TX
Relevant Jeep stats: 2000 XJ Sport, 4.0 AW4, AC (of course), NO tow package, anything else?

My AC died on me.... so I took it to the shop to get fixed and they told me that the seals on my compressor had blown because the electric fan was not coming on with the AC and that was causing too much pressure in the compressor. I don't completely understand how not moving air through a radiator would cause a pressure problem immeadiately, but these guys seem to be pretty good. At least they are friendly... so unless somebody has a good reason that that can't be true I will accept it.

So they assumed that my relay was toast - but it wasn't that. The fan will turn on - so it isn't the motor on the fan (in fact, at the moment, there is a bent-paperclip jumper in place of the relay so that the fan just stays on - is this a bad idea? they didn't think so). And the truck hasn't been overheating in the least. I don't think I'll be able to afford having someone dig through the thing and search it over till they find the problem - unless it's something really simple... in which case I could probably do it. I did check the fuses - they are all fine. I don't have any wiring diagrams for this system.

My question is: What should I check next? It's not the relay, the fuses (unless there is a third one!) or the fan itself. Is there a switch on the AC that tells the fan to turn on - or is that what the relay does? btw - the relay I am talking about is in the fuse box behind the battery. I did search btw. All I found that I hadn't tried was the "diode pack"... where is this and what does it do? Also, if the fan can run fine - then it isn't the wiring right? Ok, now I'm just rambling, aren't I? TIA for any help you can give!
 
Please?

Isn't there something else I can do try without paying someone?

Also, how can I test to see if it has worked without blowing my seals out of the compressor again?
 
I guess I'll take a shot at this because no one else has. I've got an 88 so your system may be different than mine.

I see no reason that the electric fan would play any role in blowing the seals of your compressor. My understanding of the 1988 XJ's electrical fan is as follows:

The fan comes on under two conditions:

1. Coolant temperature read by a sensor in the radiator indicates coolant temp is 215 (aprox) or greater plus or minus a few degrees.

2. Air Conditioning is selected to MAX or NORM. A relay trips electrical current to the electrical fan.

Lots of people have trouble with this fan and put a switch in to manually control the operation of the fan. Mine operates as required under the two afore mentioned conditions. I THOUGHT that it was on the hot battery bus and would run if coolant temperature requirement was met with the ingnition selected off. According to the wiring diagrams this is not the case but I would swear on a stack of bibles that it did before I replaced the radiator and had the engine rebuilt.... but I digress...

I don't see the relationship between the fan and the compressor though. I'd guess that an inproper charge of the AC could cause your seals to go or maybe the seals just plain failed due to age or manufacturing defects. Maybe your system has something in it that has caused a partial blockage that restricts flow of the R134 and increases load on the compressor.

If I were you I would ask them to explain how they arrived at the electric fan theory. If they can't do that I'd find another AC shop.

I'd test the relay and associated wiring again.

Sorry for the super long boring post.

Good luck, I hope this helps and let us know what happens.
 
Well, I can't see the relationship either - however, the fact that the electric fan is designed to always come on with the AC seems to indicate that it is important. <shrug>

Thanks though! I will talk to the shop again tommorrow and see if they can explain it to me a little better. I do trust these guys - I believe that at the very least he wasn't TRYING to rip me off... hopefully he wouldn't be mistaken about such a basic concept in his business (especially since the shop specilizes in AC work).)
 
I was just about to post that my 2000 XJ's AC has died and if anybody had some simple things to check. On the newer models should the fan automatically come on if Max AC is selected? What does the relay actually do and how do I test it and where is it?
 
it could have affected your seals. the compressor does just that, compresses the gas in the system. in doing so it heats up the gas, which causes more pressure. if there is not adequate air movement(just the regular fan) then it could possibly create enough pressure/heat to affect your seals. altho there should also be a pressure switch in your ac system that will shut the compressor off before doing damage.
 
My 98 is giving me issues right now. For the past 3 years I have been having to top off the charge, usually in the spring. I did it on thursday, like normal [it's a may thing :D ] and it would not cycle back on for more than 2 seconds, then after about 5 minutes of cycling on 2 seconds then off for 20seconds the clutch pretty well stopped responding. However the fan kept cycling on and off. In the past the fan kept pace with the compressor & clutch pretty much so I figure either my compressor is toast or the AC clutch is bad. The clutch on the compressor looks like it has been hot and is a nice toasty rusty brown color so I'm looking for a new compressor with clutch. I will probably replace the dryer tower at the same time. However before I do this I'll take it to my friends shop and see what he recommends, probably on wed, he's got the R134A stuff but not the R12. I need that AC running, don't want to go into customers sites looking like a soggy mess.
To my way of thinking if your aux fan is cycling on and off and the compressor is not engaging then then the AC circuits are functioning correctly and either the clutch is fried or the compressor is done or both. If the compressor was frozen or seized I think your serp belt would break when the AC clutch engaged..
Maybe unplug the compressor wire and stick a meter on it, turn the ac on and see if there is voltage being supplied to the ac clutch, if there is then I think the electric ckt is OK and it's a mechanical problem.
Also, my aux fan comes on with either the AC or the defrosters as the defrosters blow dry air that is first pumped over the evap in the heater box inside.
 
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RichP, might as well swap to 134, it's cheaper :D

As for the fan theory, it's just designed to make sure air flows over the coils to ensure the heat from the high pressure refrigerant is allowed to disipate. I suppose that MAYBE a slight pressure increase would be found if there was no ram air flow to assist with cooling at the condensor but you do have a engine driven fan... On the reciever/drier there is a high pressure relief valve that would allow excessive system pressure to be vented. The only electrical protection on the compressor system is the low pressure switch designed to stop the clutch from engaging if there's not enough refrigerant pressure to ensure adequate lubrication of the compressor. Seems to me that the aux. fan is there to provide airflow to increase system efficiency at lower speeds and at idle. Maybe you spend a lot of time at idle or driving a low speeds and this could be a factor? I'm still not convinced but I could be wrong...
 
That aux fan is tied into the HVAC system, when the compressor clutch is triggered on the fan is also triggered on, compressor clutch goes off so does the fan which I think means the electric ckts are working correctly. My problem is either the clutch is shot from running over the winter with low 134a in the defrost mode or the compressor is shot. I'm looking around for the best prices now and the cheapest I found is $295 for a new sanden unit.

I only mentioned the R12 for this reason. Alot of newer and new shops have not bought the equipment to cycle the R12 freon and only invested the money in the newer R134 equipment. In my case becuse I have a 98 w/R134a that means that I have no problem with taking it to a friends shop and having him evacuate the system while I replace the compressor and drying tower and will ask him if he can check for leaks before I do the compressor and tower change. That way I can order any other parts I may need. If someone has an R12 system he will do the conversion from R12 to R134 but the vehicle owner needs to locate a shop that will recover the R12 before he will work on it.

I'm just hoping that if he does find a leak it won't be in that hvac box behind the dashboard. I have NO desire to get that intimate with my XJ...
 
$295 is pretty good, I was looking around and a rebuilt is running around $250. Where are you finding your cheap parts??? :cheers:
 
Ok, new theory... after reviewing wiring diagrams that I just found I am thinking that the AC Clutch relay is responsible for telling the Radiator fan relay to turn the fan on. So how do I determine whether or not it is doing that? If the AC Clutch is working (which I can assume because it's blowing cold air, right?) then the relay itself must be working, right? Could part of a relay be toast? How can I test these things? I'm not much of an electrician, but I'm not completely ignorant (i.e. I can use a multimeter, but I don't have one...)

<Ben Stein Voice> Anyone? Anyone?

EDIT: After looking through some more... it could also be the PCM failing to give a "Radiator Fan Request" perhaps? But it looks like if that were the case the AC would fail to turn on (it looks like it has to give the request in order for the AC to come on...) I'm a little lost here...
 
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AH HA!!!!

I'm not crazy. Was looking for some fan info in the FSM and found where it clearly states that the fan WILL run with the ignition off for up to 15 min. If I can find some way to get the 20 pages from the FSM to you from PDF format I'll email them to you if you'd like.
 
I have seen that 'will run for x minutes after ignition turned off' thing too in the fsm. In all the years I've owned my 98XJ new I have NEVER had that fan kick on after shutting down. As an aside I never had gauges before this past jan or so which is when I put the new cluster in so perhaps my cooling system still works well, we'll see this summer. I think maybe the next few times I turn the engine off I'll leave the key in the on position and see if the gauge creeps up for a few minutes from residual themal like most of my past vehicles have done. It may just be not reaching that trigger point to turn the fan on...
 
I have nearly the entire FSM in PDF format. I didn't used to have the wiring diagram section of it... but it has appeared now that I need it. Not sure how - but I won't look a gift horse in the mouth. I just discovered this last night around midnight or so and spent the next few hours trying to remember what I used to know about schematics. Unfortunantly, it wasn't very enlightening because I don't remember much...

What link is there between the O2 sensor and the Radiator Fan? Page 8W-12-12 (diagram of the junction block) clearly shows a "connection" between the o2 sensor relays and the radiator fan relays (and the AC clutch relays) but I don't understand why or what the link is...??

I have noticed a drop in MPG recently, could my o2 sensor be going bad and cause both these problems? Seems far-fetched to me....
 
Yes it does. Although I'm not convinced it's as cold as it should be... it is sufficient. I wouldn't be surprised to find out that whatever is causing my problems is also preventing the AC from going into MAX mode or something... on the other hand, the last time I used the AC (just to check if it was working, was during the winter.) Perhaps my memory is just optimistic?

I am currently in the process of checking my O2 sensors. I checked my mpg from the past three or four tanks (I keep the receipts) and I have been getting ~13 mpg. This is substantionally worse than I used to get and worse than it should be in any case. This is mixed city/hwy driving. It has been a very mild winter here as well.
 
Well both 02 sensors check out (both were between 5-7 ohms across the white wires).
 
13 MPG???? That's awfull. With my road tires on, (235's) at highway speeds I get 22 MPG. In town it gets somewhere around 18. When I run 31's it drops off a couple MPGs.
 
Well my last tank went up to just above 14.... so at least it's not going down. Nonetheless, I'm gonna have to look into it. Right now though I'm more interested in making sure my AC doesn't pop again.

I tried to test the High Pressure Switch and the Low Pressure Switch today, but I'm not sure that I did it right. If I did do it right then it elimanates those as the potential problem.

I unplugged each switch (i.e. one at a time) and and connected the wires... that should have told the PCM that the switch was closed and the PCM should have turned on the aux. fan - but the fan did not come on.

The problem is, by unplugging the switches I prevented the AC itself from coming on - so maybe the PCM knew better than to turn on the aux. fan.

So, I have three questions: do yall think I wasted my time, or is something other than the switches broken?

Is the metal box with the three big plugs going into it (next to the airbox) the PCM or the ECU?

And finally, can having a diagnostic run on the PCM tell me anything useful about this problem? It would cost 45 bucks to have it run, so I don't want to waste my money.

Thanks!
 
An update and more questions... it's been awhile since I had worked on this problem because I have been moving...

So after some more testing... I have discovered a number of things. In my previous test of the high pressure switch I did something wrong... I have repeated the test and now the fan comes on whenever I put a jumper across the high pressure switch. That would indicate that the pressure switch MAY be bad.... I have also proved that the relay is working and that all the wiring is fine (because the fan did indeed come on with that test).

Some of this is just recap... Now when I got it back from the AC shop they told me the seals on the compressor were blown. This would indicate that the pressure in the compressor got too high. They claimed this was because the fan was not coming on with the AC. However, the FSM states the high pressure switch does two things: turns the fan ON at 280-320 psi and shuts the compressor down at 400-450 psi. So if the switch were bad, it could be that the fan didn't come on and caused the pressure to rise until it should have shut off the compressor, but did not. This caused the pressure to rise until it popped the seals. OTOH, I have no direct proof that the fan is not coming on when it's supposed to. It is not coming on when the AC is turned on. But I'm not willing to just let it run until the fan comes on or it blows the compressor just to find out!

So, I am fairly convinced that the High Pressure Switch is toast. Is this an expensive item? Anything I missed? (relay is fine, fan is fine, compressor is fine, it has to be the switch, right?)

If I replace the switch, how can be sure it is working without blowing out the seals if the fan does not come on? I'm really paranoid about having to fix the compressor again - I'm broke but it's way too hot for me to go without AC. I'm a cold-weather person.
 
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