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Radiator fans only come on with AC


aaron7

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Just picked up this 92 GP and trying to figure out a couple things.

 

Coolant light comes on and off, not sure why.

 

Temp gauge functions correctly.

 

Radiator fans will never come on though they work fine with the AC on. Previous owner just never turned the AC off!

 

Thoughts?

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coolant light meaning coolant level or coolant temp? and do you have the 6 guage cluster or the base one?

 

at this time of year, there is a good chance the radiator fan will never need to come on. i've idled for 20+ minutes before and never had it come on if the ambient temps were low enough. it's just a side effect of an efficient idle, low fuel usage means low heat output.

 

you would need to hook into the datastream to know if your ECM is commanding the fans on. since they seem to work with A/C usage, i would say you're not getting hot enough to need them.

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I'm in AZ. Car was well up over 220 on the gauge and they never clicked on.

 

Coolant level light is on, not overheating light.

 

I don't have a tach so I imagine it's the base gauge cluster.

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the guage sender isn't very accurate on most cars... would have to go off of the ECM's coolant temp reading for a better idea of actual temp. fan 1 on is 226*F, fan 2 on is 235*F. it's possible the coolant temp sensor for the ECM is also faulty, which would cause the fans to not come on via coolant temp, but again, would need to get sensor data to see that.

 

coolant level sensor is a common failure item, though i don't know if the base clusters had as many circuit issues as the sport clusters. could unplug it to see if it stays a solid on or off. it is right below the radiator neck.

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Well, I was just going off what the previous owner told me. Said he just left the AC on since he's owned it!

 

I did let the needle go 3/4 of the way but got scared to hurt the motor and turned the AC on.

 

The fans coming on with AC would just be an on/off and not in the ECU, correct? A solenoid/relay somewhere that also bumps up the idle?

 

So the fans get the signal to come on from the ECU which ONLY gets the temp signal from the one coolant temp sensor below the radiator filler neck, right? Makes me worried as the gauge seems to function correctly (albeit not very accurately) so I'd imagine the sensor is working. That'd mean the ECU is getting the temperature from the sensor but not sending the signal to the fans to come on.

 

Whew. I'm lost haha

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the ECM tracks the "request" for the A/C compressor to come on from the HVAC panel in-cabin. it will then turn the fans on IF the A/C compressor kicks on and enough pressure builds in the system to require additional airflow across the condensor. they'll go off if the compressor is no longer requested by the driver, pressure drops low enough, or when above ~70MPH. it's an intelligent control scheme for the fans, all controlled by the ECM. idle speed is attempted to be compensated for when the compressor engages and again when the fans come on. there may be a slightly higher idle speed as a result.

 

the temp sensor the ECM uses is actually mounted in the lower intake manifold IIRC.... the one that drives the guage is actually in the head, and the level sensor is in the radiator.

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Hmm, so the coolant low light even though it's full may be the sensor on the radiator? I'll have to try replacing that.

 

As for the fans, any chance there's an online shop manual for these cars so I could locate that sensor in the manifold? I know for many of the cars I've had people have uploaded them. Otherwise I'll have to go spend the $20 on one! :)

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here is the best i could pull. the sensor the ECM uses is located directly underneath the thermostat. images 1 and 2 should help here.

 

the sensor for the guages.... i'm not 100% on it, the view given isn't very good. at the very least, i seem to remember it having a unique, 1-pin connector. image 3 for this one. looks like it might bein the lower intake as well instead of the head?

 

http://imgur.com/HyjsH7F,azJx6Ve,3wSkraB

 

also, sometimes even just cleaning the coolant level sensor fixes it.

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