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3 different probs


 
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matt the pilot
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Joined: 22 Jun 2007

PostPosted: Tue Jul 17, 2007 1:48 pm    Post subject: 3 different probs Reply with quote

Ok 3 different problems...

This is a 95 Cherokee 4.0

1.) Brakes have no power to them, is it the brake booster? All vac lines are in place.

2.) The electric fan does not turn off when I turn the car off. I have to unplug it.

3.) The A/C is not blowing cold. I checked the pressure and it was in the red (as in way too much pressure). The clutch never engages on the compressor either. Bad compressor?

Thanks for any help guys.
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kaos
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Joined: 10 Jan 2006
Location: Iceland

PostPosted: Wed Jul 18, 2007 10:26 am    Post subject: Reply with quote

1.) Hard to say. It certainly could be the booster, but it might also be a stuck wheel cylinder, clogged brake line, et.c.

2.) The electric fan shouldn't neccessarily turn off as soon as you turn the car off. It is controlled by a thermoswitch, and doesn't turn off until the engine has cooled somewhat down. If it doesn't turn off within a few minutes after you've shut off the car, you probably have a defective thermoswitch.

3.) Are you sure that the reading you got was overpressure, rather than underpressure? The A/C system incorporates a pressure switch that prevents the clutch from engaging if the pressure is too low. The only ways I can think of that you could get overpressure are, a) that the system has been overfilled, or b) blocked lines, and then only on the pressure side of the circuit, and with the pump running.

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Kári
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mattbred
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Joined: 03 Jun 2007

PostPosted: Wed Jul 18, 2007 11:57 am    Post subject: Reply with quote

Doesn't the ignition need to be on for the electric fan? That's what it says under the hood.
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kaos
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Location: Iceland

PostPosted: Wed Jul 18, 2007 1:20 pm    Post subject: Reply with quote

Quote:
Doesn't the ignition need to be on for the electric fan? That's what it says under the hood.


You are absolutely correct. Mea culpa, my fault, et.c., et.c.

In a moment of abberration I was going from general principles, instead of actually consulting the service manual for the vehicle in question. On many cars the cooling fan does work as I described, but on the Cherokee (at least my '93 model that I have a service manual for) it doesn't.

Which brings us back to square one. Why doesn't it turn off as supposed to? Going by the wiring diagram in the service manual this time, it appears that actually the fan is controlled by the ECM, instead of a seperate thermoswitch, but the ECM should also shut down (apart from memory backup) when the ignition is turned off. I think the ignition switch should be checked before proceeding further.

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Kári
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DavidXJ
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Joined: 07 Sep 2006
Location: Visalia, CA

PostPosted: Wed Jul 18, 2007 1:53 pm    Post subject: Reply with quote

The first thing I would do when trying to solve the fan problem is switch out the relay that controls it. The relay is pretty standard, so finding another one to temporarily swap with it shouldn't be too hard. If you swap it and it still stays on, then at least you've eliminated one step.

When it comes to the pressure switch for the AC, they sense both too low and too high of pressure. So if for some reason there is too much pressure in your system, it will never allow the clutch to engage. How it got too much pressure in the first place I have no idea. Your ECM could also be screwed up. My brother-in-law;s Cherokee would start blowing hot after the engine would warm up. They checked the compressor, the charge, and the pressure switch, but it ended up being the ECM. Replacing it fixed the problem.

If you want to know if your pump is bad, hot wire the relay so it will force the clutch to stay engaged. But don't run it this way for too long because your lines will eventually freeze up (if the system is working) and then your pump will be shot.
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ThePhantum
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Joined: 23 Jan 2004
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PostPosted: Wed Jul 18, 2007 6:04 pm    Post subject: Reply with quote

If the compressor never actually switches on and the system is showing too much pressure, then someone tried adding refrigerant thinking that was the problem. It's also possible that someone tried to charge the system when it was working and overcharged it, so now it won't run. The first thing to do is to vent the excess. Despite what you might hear, it's illegal to vent any type of refrigerant (including R134a) to the atmosphere. So unless you have access to a recovery system, you'll need to take it to someone who does. At that point you can start troubleshooting.

Does the electric fan run all the time? It's only supposed to run when the A/C is on (since that's not working, it's a moot point) or when the engine temp hits around 218. If it always runs, you probably have a short or bad relay. Also, since the electric fan is keyed off the A/C, it's possible that the ECM is the problem.

As far as no power brakes, if there are no pulls to the right or left under braking, it's most likely not a blocked line or frozen caliper/wheel cylinder. You said all the vacuum lines are in place....but is there actually vacuum on the line going to the booster? If there is, then my guess is that the booster is bad.
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Brad The Best
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Joined: 14 Jan 2007
Location: Kamloops B.C Canada

PostPosted: Wed Jul 18, 2007 6:25 pm    Post subject: Reply with quote

ThePhantum wrote:
Despite what you might hear, it's illegal to vent any type of refrigerant (including R134a) to the atmosphere. So unless you have access to a recovery system, you'll need to take it to someone who does. At that point you can start troubleshooting.


and it really stinks , like just awfull . or maybe thats just R12 , i haven't accidentally broken a line with an excavator on a r124a equipped system . now you may be saying why did you have an excavator bucket under the hood of a car , lets just say i didn't want to go get a snipe for my wrench and it was right there ... like come on , it was a good idea at the time . Smile
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matt the pilot
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Joined: 22 Jun 2007

PostPosted: Thu Jul 19, 2007 11:33 am    Post subject: Reply with quote

As far as the A/C goes, it definately has too much pressure. What I did notice was that for some reason the clutch electrical line was unplugged. I plugged it in, clutch kicked on. No cold air. I relieved the pressure to where it should be, still no cold air even the clutch is still on.

Onto the radiator fan... the fan turns when I turn the A/C switch on and turns off when I turn the A/C switch off. It also, ofcourse now that I'm trying to figure out what's wrong with it, is now turning off when I turn the car off. Go figure.

Also I was curious what do you guys' temp gauges hang around? Mine seems to be liking the 210 degree mark. Maybe just under a needle's width the 210 mark.
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ThePhantum
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PostPosted: Thu Jul 19, 2007 1:22 pm    Post subject: Reply with quote

Right around 210 is normal operating temperature.
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matt the pilot
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Joined: 22 Jun 2007

PostPosted: Thu Jul 19, 2007 9:56 pm    Post subject: Reply with quote

^^^ Thanks. I am having some overheating problems with this thing still. Gonna flush out the radiator, put new coolant, change the thermostat, see if that helps. I'm also starting to have alternator problems. As of right now the alt ain't doing shit. If I disconnect the batt the car stops running. It's been doing that on and off. I just hope it's the alt itself starting to go out and not some wiring gremlin. I'm gonna swap in a new fan relay also.
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mattbred
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Joined: 03 Jun 2007

PostPosted: Fri Jul 20, 2007 12:02 am    Post subject: Reply with quote

matt the pilot wrote:
^^^ Thanks. I am having some overheating problems with this thing still. Gonna flush out the radiator, put new coolant, change the thermostat, see if that helps. I'm also starting to have alternator problems. As of right now the alt ain't doing shit. If I disconnect the batt the car stops running. It's been doing that on and off. I just hope it's the alt itself starting to go out and not some wiring gremlin. I'm gonna swap in a new fan relay also.


Do NOT under ANY circumstances remove your battery while the jeep is running! Ack! It can sends huge voltage spikes to everything electrical. If it was a carb itd be fine, but.. Its run by a computer that doesnt like voltage spikes. Absolutely never use this method on an EFI vehicle to test if the alternator is working properly. Use a volt meter. 14 volts and its working. Under 13 and its not.
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matt the pilot
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Joined: 22 Jun 2007

PostPosted: Fri Jul 20, 2007 11:54 am    Post subject: Reply with quote

Hmm. Interesting. Learn something new every day. So uhh... yeah... that never happened then... Haha
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mattbred
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PostPosted: Fri Jul 20, 2007 12:39 pm    Post subject: Reply with quote

matt the pilot wrote:
Hmm. Interesting. Learn something new every day. So uhh... yeah... that never happened then... Haha


Aha, well its just good advice. I didnt even know of that until a little while ago.

It sucks from the old days where if it didnt run, its a few simple things. Now with computers and sensors its ugh. But when it runs it runs nicer.
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matt the pilot
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PostPosted: Fri Jul 20, 2007 1:02 pm    Post subject: Reply with quote

mattbred wrote:
matt the pilot wrote:
Hmm. Interesting. Learn something new every day. So uhh... yeah... that never happened then... Haha


Aha, well its just good advice. I didnt even know of that until a little while ago.

It sucks from the old days where if it didnt run, its a few simple things. Now with computers and sensors its ugh. But when it runs it runs nicer.


So true... I'm coming from a '69 Ford F100... Where if I need to work on it I sit on the inner fender wall and place my feet on the headers. Haha. Spark and fuel what ya looked for back then.
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matt the pilot
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Joined: 22 Jun 2007

PostPosted: Fri Jul 20, 2007 4:18 pm    Post subject: Reply with quote

Now I'm getting a code that says "Coolant sensor out of range". I assume this is what plugs into the thermostat housing cause that's the only thing I unplugged. Out of curiosity if this sensor were bad could this be what's causing my fan to stay on?
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