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Old 07-02-2015, 09:00 PM
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radiator fan always on - almost

My daughter has a 2003 Liberty Limited 3.7 4WD which I am trying to fix.

Recently I have been trying to diagnose radiator fan problems...without going into where I started, I will just say where things are now...

I have replaced the fan relay and the coolant temp sensor. The problem is that when I start the motor the fan goes on immediately (regardless of engine temp) and I believe it is on high speed (assuming my jeep has high/low speeds).

Anyway, when I turn the engine off, the fan continues to run. Anywhere from a minute or so to twenty minutes or so. I am worried at some point, the battery will die.

I also have noticed that the A/C is not as cool as it should be and the compressor cycles on/off seemingly too frequently.

I am wondering if the fan always on and the A/C issue could be related and maybe the A/C pressure sensor might be faulty.

Or maybe something else causing the fan to run too much.

I probably don't have enough details here, but any help would be appreciated.

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Old 07-02-2015, 10:46 PM
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Re: radiator fan always on - almost

I really may be no help.....but have you tried a new tstat?
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Old 07-03-2015, 08:04 AM
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Re: radiator fan always on - almost

thanks for the idea, but I ruled out the thermostat for 2 reasons, first there is no problem with the engine temp and second, there is no electrical connection to the thermostat and I think the unnecessary running of the fan is electrical related.

Am I missing something?
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Old 07-03-2015, 08:23 AM
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Re: radiator fan always on - almost

The compressor cycling on/off too frequently could be due to a low refrigerant charge, but also a faulty AC pressure transducer. Now i don´t know if your jeep has a pressure transducer, or a low and high pressure switch, but i expect it to have a pressure transducer. The pressure transducer signal is used by the PCM to control the compressor clutch, but also the cooling fan. So a faulty pressure transducer could indeed cause the cooling fan to run when it is not suppost to, but also cycle the compressor at wrong intervals. I would expect the sensor to be faulty in a high pressure position.
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Old 07-03-2015, 11:00 AM
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Re: radiator fan always on - almost

Thanks Frango. turns out the A/C freon was low, topped it off and now the compressor is properly staying on and the inside of the car is blowing cool air.

i was hoping this would fix the fan running but it didn't. still coming on immediately and running for a while when i turn off the engine.

so yes it has a high pressure transducer and a low pressure sensor. not sure at this point if the transducer is bad, since the compressor stays running.

i'm stuck at this point, any other ideas?

thanks again.
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Old 07-03-2015, 01:26 PM
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Re: radiator fan always on - almost

Some sensor is telling the PCM to switch the cooling fan on. Are you sure your AC system has a low pressure SWITCH and a pressure TRANSDUCER?
It is the pressure transducer who should tell the PCM to switch on the cooling fan, so i would see if there is any test procedure for this transducer.
Did you check the connector on the pressure transducer and clean it with electrical contact cleaner?
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Old 07-06-2015, 07:18 PM
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Re: radiator fan always on - almost

Thanks again Frango.

I decided to take it to pep boys for diagnosis. they said the A/C pressure transducer is fine, that the problem is that the PCM is sending a signal to the relay to run the fan after the engine is turned off.

So I'm going down the path of replacing the PCM.

Do you (or anyone) have experience replacing the PCM?

Should I get a used one from a junk yard and get the dealer to flash it, should I order online (which I am suspect of), or I am thinking maybe something like an autozone...a bit more expensive than online, but they have a pretty good reputation.

thanks...
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Old 07-06-2015, 08:41 PM
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Re: radiator fan always on - almost

I have no schematic manual for your jeep, but most probably also the transmission temperature is an input to turn the fan on. I would expect that if the PCM is faulty, that it will keep the fan on all time, and not switching it off after a certain time. I would at least have a look with a scanner to check the transmission temperature indication, before spending money on a new PCM.
A junkyard PCM could be an option when you go that route, but you never know what you get. No experience with the online shops myself.
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