My 1990 740 volvo turbo wagon has the cooling fan running and draining the battery, how do I turn it off?

Does your vehicle have pressure switches on the bottom of the condenser? One of these can be faulty and cause the fan to run constantly. I had this problem on a 94 940. My son has the car, so I can't check the switch color.

I unplugged the switch to prevent the problem. Later, we installed a toggle switch on the dashboard and tied it into the wire pigtail for this pressure switch, so that he could activate the fan manually if the engine was going to overheat.
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94 940 n/a 320k+ and rolling, owned 18 yrs; 05 XC90 2.5t for the wife; sold 92 745T; sold 88 764T

Disconnect the fan relay. It should be identical to the RSR. If you disconnect the wrong one, the car won't start (no power to fuel injectors).

There may be a short in the sensor, the wiring to the sensor, or the old RSR may have its contacts fused together, so it can't break the circuit.

I've tested my AC fan and relay several times by simply shorting the two connectors for the fan sensor together.

maybe clean all the grounds??

Thanks guys for the suggestions however the problem persists the fan continues to run once the battery is recharged, even the mechanic is puzzles, any other ideas?

As Chris suggested check the temperature sensor at the top passenger's side of the radiator. Disconnect the two wires and should stop the fan. Put the probes of a VOM on the sensor contacts. That should show open (no continuity) when the car is at ambient temperature. If not I would call the sensor defective.

If the sensor checks out did you try simply swapping the two identical relays on the shock tower? If that restores normal function the relay that was controlling the fan is defective.

Randy


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Any twenty minute job is just a broken bolt away from a three day ordeal

You can first try disconnecting the temp sensor in the radiator. If that doesn’t kill it then it might be a stuck relay which is located next to the identical looking Radio Suppression Relay on the RH side of the engine compartment in front of the coolant bottle.