I have a 91 accord and the radiator fan has started to come on randomly, even when the vehicle is stone cold and has been sitting all night. I have already replaced the fan relay. I checked the thermoswitches by unplugging them while the fan was running, it had no effect. I also shorted the contacts on the thermoswitch plug while the fan was running, that also had no effect, the fan kept running, the vehicle had been sitting all night and was cold. Please advise. Thank you.

 

It stays on 100% of the time as soon as ignition is switched on?

 

It comes on when the ignition is off, when the key is out, in the middle of the night randomly. I insert the relay in the morning before starting, sometimes the fan comes on right away, sometimes it does not. When I get to my destination and the engine is hot, sometimes the fan is on, sometimes its not. I then remove the relay to prevent the fan from draining the battery. Any thoughts?

 

I think it's either a faulty thermo switch or a short in wire somewhere.

 

Does your Accord have A/C or not? They have slightly different fan circuits.

 

I looked at both circuit diagrams for the 90-91 Accord (with A/C and without). If you have already tried unplugging coolant temperature switch B (the one located on the right front of the engine, in the coolant outlet) and it still does the same thing (e.g, fan continuously runs with ignition off or cold), then my guess would be a faulty cooling fan timer unit.

The cooling fan timer unit is located behind the left side of the dash.

 

Yeah, if the cooling fan timer unit was working properly you would be unable to get the fan to run at all by jumpering switches with the key turned off. Unless the key was turned off within the last half-our or less.

Have you swapped relays around to rule out a bad fan relay (randomly closing the circuit in the middle of the night)?

 

Just me but "which fan" is coming on - Drivers or pass side? The timer is only going to control one of them.

Also the relay for drivers side fan is located on the drivers side of the car - behind the headlight and not in the underhood fuse box.

 

We still don't know whether the OP's car has AC or not, as OP never answered that. If it doesn't have A/C, then there is no condenser fan due to no A/C condenser.