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Need help understanding thermostat housing sensors

4g6Tree

Active member
Joined
Jul 7, 2014
Messages
44
Location
Salem, VA
I'm having a little trouble understanding what these sensors do and which one(s) affect fan operation. I see the image below all over the site so it'd probably be a good reference. Here are my guesses but if anyone knows better than me please fill in the blanks. The wires to all of these sensors have broken off on my car, and the radiator fans don't work. I'm mainly trying to figure out what sensor turn the fans on, but it'd be nice to know what each of these does.

1. Engine Coolant Temp Gauge Unit -
Sends a signal to the temp gauge in the dash

2. Engine Coolant Temp Sensor -
Sends temp signal to the ECU?

3. Air Conditioning Engine Coolant Temp Switch -
Disables AC if the temp gets too hot?

4. Engine Coolant Temp Switch
Main temp switch that turns fans on?

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transparentdsm

Well-known member
Joined
Jul 27, 2011
Messages
3,690
Location
Cherry Hill, NJ
the main fan switch is the lower sensor on the radiator.

1 - gauge cluster temp

2 - what the ecu reads

3 - switch for compressor clutch

4 - fan in front of a/c condenser

your going to have to trace all the wires back. the ECU one is extremely important for driving as is the dash one unless you have an aftermarket set up. if you dont have A/C the rest are useless.

on the stock main fan there is a resistor that tells the fan what speed to run, high or low, and when it shorts out the fan stops spinning. you can bi-pass the resistor and run the fans on high only. this is only an option and my real recommendation is find a good resistor and replace all parts properly.
 

4g6Tree

Active member
Joined
Jul 7, 2014
Messages
44
Location
Salem, VA
Thank you, I was able to solder and shrink wrap the #2 sensor connector so it's working again. The connector to the sensor in the bottom of the radiator was broken, luckily I had a spare and I replaced it. Now the main radiator fan on the passenger side will turn on when the coolant temp reaches 215. But the AC fan will not turn on unless the AC is actually on. Would this be a result of the #4 connector not being hooked up?
 
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