over heating aux fan questions
Senior Member
Joined: Aug 2011
Posts: 760
Likes: 6
From: Landers, CA
Year: Several
Model: Cherokee
Engine: 4.0
When the dash AC switch is on, it signals the PCM to turn on the fan - via the relay - overriding all other inputs - no matter if it's cold out or not. It should not cycle - stays on no matter what, even if the AC has no Freon and doesn't work. It's purely an electrical command.
AC off - when the temp is right at the "turn on" temp - 220 or? (determined by that sensor in the t-stat housing,) the fan comes on. When it's on and the temp drops a little, fan goes off. Normal.
The sensor could be going bad if it's cycling too much - look up the definition of HYSTERESIS - if it's too close it will seem like it's cycling on and off. Changing it with the resistor will move the cut points and probably stop the cycling.
The other function of that sensor is to tell the PCM it's no longer "cold", so when everything else is right it can go into closed loop.
AC off - when the temp is right at the "turn on" temp - 220 or? (determined by that sensor in the t-stat housing,) the fan comes on. When it's on and the temp drops a little, fan goes off. Normal.
The sensor could be going bad if it's cycling too much - look up the definition of HYSTERESIS - if it's too close it will seem like it's cycling on and off. Changing it with the resistor will move the cut points and probably stop the cycling.
The other function of that sensor is to tell the PCM it's no longer "cold", so when everything else is right it can go into closed loop.
Seasoned Member
Joined: Dec 2010
Posts: 287
Likes: 1
From: Houston
Year: 1996
Model: Cherokee
Engine: 4.0 I6
Originally Posted by Johnthepanpire
You could always wire a toggle switch in the cabin to the fan.
A lot of people on here have had to do that, me being one of them. It only takes like 30 mins and maybe $10 worth of parts.
I had replaced my coolant temp switch and the relay and it still wouldn't come on by itself.
You might want to hot wire the fan and make sure the motor is ok too.
A lot of people on here have had to do that, me being one of them. It only takes like 30 mins and maybe $10 worth of parts.
I had replaced my coolant temp switch and the relay and it still wouldn't come on by itself.
You might want to hot wire the fan and make sure the motor is ok too.
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