my cooling fan is always on. this is what i've done so far. hvac equipment completely removed from car including all the little ecu boxes that was attatched to the hvac box. i've heard you'll need to ground the high pressure switch so the fans won't come on all the time and i have but fans are still on. i removed a/c fan relays and still getting power to the fan. could the coolant temp switch be bad (the one on the radiator)? is there any way of testing?
yes. unplugging it and use a paperclip to jump the 2 terminals together. in fact i don't remember if unplugging it will turn them off or on. try both ways, one of them will turn them off.
i think it turns it on as part of a saftey system to have fan all the time so the car doesnt overheat due to a switch issue...
What I've learned again tonight .. both the A/C High Pressure Switch and the Temperature Switch are in series. Both should be closed for the Radiator Fan Relay No 1 to be open and thus turn off the Radiator Fan. So when the car temp is below 180 F (90 C), the Temp Switch is closed. I verified this with my multimeter. Then I checked the Fan Relay No 1 and verified that it is closed state when not activated and open when activated. Next I disconnected the blue connector that goes to the A/C High Pressure switch and made a jumper with a small paper clip to short the wires. (This connector is below the windsheild wiper motor). Now my fan is off. I have an '87 Celica BTW.
-thread is pretty old, but yes you have to permanantly jump the blu connecter comming off the harness at the firewall below the wiper motor. -i just took the other side of the connecter, removed the wires and then made a jumper connecter. no worries on a wire/paperclip falling out. -you can then use both fans and they will work in unison normally. -ive seen loads of blown motors at the track on cars with a manual switch...lots of other stuff to think about besides remembering to turn the fans on....
holy batman thread revival! anyway, i've had this problem since i've own my car. here's the rundown: 1987 USDM GT-S (3S-GE) 1) previous owner had hardwired the fan to a pin in the A/C fuses fusebox (in front of battery) so it's on as soon as you turn the ignition to "on" 2) recently i've found the two wires that were cut in the harness that connects to the fans, however the fan is still on with the ignition to "on" no matter what temp. 3) dave had advised me to check my Fan Relay in the fusebox beside the battery, swapped it with the same relay (Relay B4 Part#90987-03001) from an AW11 mr2 with fans that operate properly at the right temps, still the same thing 4) swapped the coolant temp rad switch on the thermostat housing (1 pin white plug) with one from a 4A-FE corolla as the one on my car was bent, same thing basically some other observations/tests - pull fan relay = fan off (but at least i now know that the fan is wired into the harness correctly again) - ground the wire that goes into the coolant temp rad switch = fan still on. i'm looking for another way to diagnose the fan circuit. also, my motor (and perhaps the wiring harness) is from another donor GT-S and perhaps it had A/C, from what i've heard, the A/C circuitry goes in parallel somehow with the fan switch. if that's the case, perhaps i could put a relay somewhere in the a/c fusebox even if my car has no A/C. this is now a big issue to me as with the aluminum rad, every time my thermostat opens, my coolant is ice cold and makes the engine temp go down a little bit before the thermostat closes again. this is most likely a faulty (1 month new) thermostat, but might as well cover all my bases. thanks in advance guys.
The cooling fan circuit is designed as a fail safe system meaning that if the temp sensor fails the fan will still run. The circuit is designed to have the sensor turn the fan off when not needed. The cooling fan circuit uses a normally closed relay. Most relays are normally open. So in the cooling fan circuit the relay sends power to the fan while it is not receiving power from the temp sensor. When the sensor sends power to the relay the relay opens and the cooling fan shuts off. So the sensor can fail, the connection between the sensor and relay can fail, or the relay itself can fail and all will resut in the relay staying in the normally closed position causing the fan to stay on continuosly.
I would not really recommend this idea but a common winter trick to increase heat is to cover some of the surface area of the radiator so not as much air flows through the radiator. You'll see a lot of big rigs useing this idea in the winter
alright, so what i did was take off the wire from the the water temp switch and ground it. once that happens, the relay should have opened and turned off the fan. however, the fan was still on. leads me to two things -wire from water temp switch to pin 2 of fan relay is somehow dislodged/cut -relay is dead. however, i used another relay and i get the same result. i'm gonna try to go directly to the relay, ground pin2 and if the fan turns off...time to find where the wire has failed...
hopefully i don't have to resort to that, i'd rather have a thermostat that opens at 192F instead of 180. update on the rad fan issue: i checked continuity from the water temp switch wire to pin 2 of the fan relay and it was 0, so somewhere along the harness there is a problem. i've put a temporary wire from pin 2 directly to my water temp switch as the wiring diagram shows and the fans turn on and off normally now. basically i've had the unfortunate circumstance of the wiring being the problem and the relays/sensors working properly. the only other explanation is that the harness i have is from a car that has A/C and that the A/C pressure switch is an open circuit. according to the wiring diagrams, this switch is the only thing in between pin 2 of the fan relay to the water temp switch IF you have A/C in the car. i'm not quite sure where this is however... i'll consider this fixed now because i've narrowed down the problem. thanks dave for your help especially the wiring diagrams. now the only wiring issue i have is the hvac air diverter on my car.
Check these points circled in red on your circuit board you can see where they have broken re solder them and your temp slider should work
unfortunately, i've resoldered EVERY pin on two separate hvacs to no avail. i'm pretty sure this is another wackjob wiring from the PO
