My son just bought a 1998 Civic Dx about two months ago. Last week it overheated. It seems like the coolant fan is not coming on. My first question is; Is the coolant fan suppose to run when the A/C is switched on? It doesn't on his car. We have checked the under hood fuse, which was fine. We switched the coolant fan relay w/ the condenser fan relay, and only the condenser fan still came on. We ran 12volts to the fan and it came on. Replaced the coolant temp sensor and the cooling fan switch, same problem. Right now we have 12volts running to the fan when ever the car is running. So, what is the next step? Thanks in advance.

 

The A/C and radiator fans are independent of each other. Since the radiator and condenser are side by side they don't share the same airflow like most cars do.

Plug everything in stock again except unplug the temperature switch on the thermostat housing and jumper between the 2 pins in the plug. The fan should now run whenever the key is on. If it doesn't check the fuse, relay and wiring. Make sure the relay coil is getting power. I think this comes from the same circuit that runs the engine so it wouldn't run without it, but not sure. The contacts in the fuse box may have melted.

 

Yeah, I already put in a jumper wire like you suggested and the fan does run. I'll check for relay voltage when we are both home.

 

This outcome indicates that the "new" coolant temperature switch on the thermostat housing is faulty.

 

That's what my wife said!! But from what I can tell, it's a coolant fan switch in the thermostat housing, and the temperature sensor is in the block below the distributor?

 

Correct, the switch is in the thermostat housing and the 2-wire sensor is below distributor next to the 1-wire temperature sending unit. Your "new" switch is likely faulty. Return it for a new one.

 

Would teflon tape on the threads of the switch cause it to not work right?

 

I don't think teflon tape would cause a problem, though it should not be necessary if you replace the O-ring.

Did you top off and bleed trapped air from the cooling system after replacing the switch?

 

Yes, and the car is running fine with the switch by-passed, so I'll stop and get another fan switch. Thanks for your help.

 

Good luck with the hurricane.