I need some control advice for my 98 Civic EX. The radiator fan switch works but according to all the books, the fan should come on when the AC is on regardless of temp switch. After looking at the wiring diagram, I see that the temp switch controls the ground. That same green wire goes to the PCM. How does the AC turn on the fan? Any advise will help. Thanks

 

Unlike most cars, the 92-00 Civics have a side by side placement of the radiator and A/C condenser as two independent units each with their own air flow. Thus the A/C operation is independent of the radiator fan. Only the condenser fan should come on when the A/C is on. The radiator fan is controlled only by the coolant temperature sensed by the switch on the thermostat housing.

 

I thought so by looking at wiring diagram but the books kept telling me different.
I didn't know if the PCM closed a contact when the AC was on or what. Thanks for clearing that up.

 

On my '01 EX Coupe (5-sp MT), both fans come on with the A/C engaged, and neither come on at any other time (which is a problem, I beleive).

 

The 01 has the more conventional arrangement of a full-width condenser in front of the radiator. So both fans should come on with the A/C to cool the condenser. Does the engine overheat because the fans don't run other times?

 

No, the engine has never overheated and I've never noticed the fans running without the A/C ON. But, after 13 years of service and 386K miles, I think I should probably replace that thermal fan switch as a PM action to ensure that the fans would come on if temp exceeded 199 F (93 C). Looking at the schematic, with motor runing I can test the circuit from the switch out to the fans if I pull the plug off the switch and ground the GRN wire contact. That should activate the RAD and COND fan relays and the fans should come on.

On another note, once again while driving 70mph my TEMP guage dropped to COLD , as if the car were off, and hung there for 40 miles till I pulled in the parking lot of my gym and shut the car off. Later, I drove home and the TEMP read normal at slightly lower than 3:00 on the dial. Both radiator hoses indicate hot water is flowing. I don't think it's the guage..probably the ECT sensor. I don't think a stuck thermostat would make the car read COLD on a 85 degree Florida afternoon at 70 mph.