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Tim Mohr
Tim Mohr, ASE Master Tech
Category: Honda
Satisfied Customers: 15593
Experience:  30 YRS EXPERIENCE, FOREIGN AND DOMESTIC, GAS AND DEISEL
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Coolant fans only come on in '02 Civic with AC on.

Customer Question

Coolant fans only come on in '02 Civic with AC on. Previously replaced radiator and thermostat which resolved overheat problems, BUT it was summertime and ran AC constantly. First frost and turned on heater. Boom! Temp hits 75% of max and I pull over, kill the engine and purchase a bottle of 50/50 coolant, added to radiator once it cooled down a bit. That's when I discovered fans not running and checked fuses, relays. All work. Turned on AC? Fans come on.
Submitted: 1 year ago.
Category: Honda
Expert:  Tim Mohr replied 1 year ago.

Hi, my name is ***** ***** is usually caused by a bad coolant temp sensor, it wont turn on the fans, until the coolant reaches 210 degrees, if the sensor is bad and readong low, they wont come on, have you checked the reading of the sensor with a scanner to see what the computer is seeing as the temp?

Customer: replied 1 year ago.
Have not. Have just been driving with the AC on and a bottle of antifreeze in shotgun. I need to verify that the coolant fan switch is functional, and not shorting somehow.
Expert:  Tim Mohr replied 1 year ago.

THERE IS NO COOLANT FAN SWITCH, THE COOLANT TEMP SWITCH SENDS THE SIGNAL TO THE COMPUTER, AND THEN THE COMPUTER SENDS THE SIGNAL TO FAN RELAY TO TURN IT ON, IF THE FAN COMES ON WITH THE A/C, EVERYTHING FROM THE COMPUTER TO THE FAN IS GOOD, THIS JUST LEAVES ABAD TEMP SWITCH OR A BAD COMPUTER, FIRST THING TO DO ISNSEE WHAT SIGNAL THE TEMP SWITCH IS SENDING TO THE COMPUTER, IF ITS TOO LOW, THEN REPLACE THE SWITH, IF IT IS GOOD, THEN IT CAN ONLY BE THE COMPUTER,TIM