I have been trying to get my electric fan to operate on my 1992 944 non-turbo with no luck. There is no thermal switch in the side of the radiator or in the bottom hose. I can’t find any evidence of a thermal switch anywhere except for the engine temp. switch under the intake manifold. The relay has two small wires going to it that are obviously the thermal input to tell the fan to start, but I can not figure out where they vanish in the harness. Does anybody know how this model signals the fan to run?

Thanks,

If I am reading the wiring diagram correctly, the fan relay is supplied a ground path by the ECU to activate either the high or low rpm side of the cooling fan. Are the two relay wires you mention a blue/black(low rpm) and a white/black(high rpm) wire? These are the trigger wires. If you supply either with a ground the cooling fan will operate. The fans are also turned on by 2 sensors in the a/c system. a low pressure switch for low rpm fan, and a high pressure switch for high rpm fan operation. The ecu determines when the fan should turn on and at what rpm it should run at as determined by the engine coolant temp. sensor.

< Are the two relay wires you mention a blue/black(low rpm) and a white/black(high rpm) wire?>

Those are the colors all right! And it makes sense that the signal comes from ecu as there seems to be no other source. (Also, no go with AC on) After reading this I grounded both wires (one at a time) neither will turn on fan. Relay makes noise however. I know this fan will work when hooked to the battery directly. What do you think? Bad relay?

Thanks for the help!

You could check the output from the relay to see if it is supplying the 12 volts to the fan. With the blue/black wire at the relay grounded there should be 12 volts present at the green wire. If the white/black wire at the relay is grounded there should be 12 volts present at the red wire. If there is 12 volts at both of the wires at the relay then the wiring to the fan or its connector is bad. If you jump between the 2 red wires on the relay the fan should run at high speed. The low speed fan should run if you jump the red wire supplying 12 volts at the relay to the green wire. If the fan runs in both of these instances than the relay is definitely bad. Let us know what you find out.

John,

Thanks for the great info! When checking the relay with blue/black wire grounded I get 9.9 volts at the green terminal. (12 volts present at red in) With white/black grounded, I get 9.6volts at red terminal (red green connector to fan disconnected for this test)

When I jump the red in and red to the fan the voltage drops to zero. Same thing happens when I connect red in to the green wire to fan.

This voltage drop happens with my original fan and the used one I got from the dismantler. Is it possible I got a bad fan by coincidence or am I some how breaking them? I don’t know much about motors, should I get continuity between ground and red or green?

Thanks again you have been a great help!

If the voltage drops to zero when you connect the red battery power lead on the relay to either of the fan power leads at the relay it appears that the red 12 power wire is not supplying the necessary current needed to run the fan. What happens when you take 12 volts directly off the battery and connect it to the red power lead at the relay and then ground the blue/black wire? The fan should run at low speed. If you ground the white/black wire the fan should run at high speed. If the fan now runs find out where the connection is bad for the relay power feed wire.

Electric fan may only be activated by turning on the AC. Try that and see what happens. I have heard that the newer Volvos have a larger cooling capacity and therefore only use the fan as a way to keep the AC cool at idle. Also, is the radiator a 3 row?

two row, no go with AC!