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940 Turbo, radiator fan comes on when it's cold on first start

herbiedriver

herbiedriver

Member
Joined
Sep 20, 2022
Location
Boulder, CO
Been trying to troubleshoot this, when it's below 30° (F) outside and I start the car, 94 940 turbo, it will idle for about a minute and then the radiator fan kicks on, obviously it's not even close to temp... replaced the coolant temp sensor under the number 3 intake runner, and made no difference, put the old one back in...

Also, car idles great when cold, but when it's warm and been driving it for about 10 minutes the idle starts to surge, don't know if that's related, but had to mention that as well.

Ideas?
 
PCH said:
May be one of 3 pressure sensors in the condenser is bad and is triggering the fan relay. Are you sure the AC is not set to be on?
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Absolutely positive the AC switch is not on, that was my first thought, or even that I had something set for defrost, which on my VW it runs it through the AC circuit to dry the air. It only happens when the outside temp is below 30ish... AC works normally in the summer as well.
 
What do you think can trigger the high pressure switch to close a minute after starting the car besides the compressor being on?
 
PCH said:
What do you think can trigger the high pressure switch to close a minute after starting the car besides the compressor being on?
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Looking through wiring diagrams, there are 3 sensors on the condensor, the two on the far right (looking at car) are connected to the fan via the relay and the Jetronic Control Module is in that circuit as well... So may have to go and check those pressure switches to see if they are open or closed when cold, looks like they should be open until pressure says otherwise
 
All the relay needs to pull in your fan (presuming the fan motor is good, and relay is working, BOTH assumptions) is a ground path for the relay.

OP, check and see if your relay has near 0 ohms on the ground pin when checked back to the battery. Without that path, nothing happens. From memory, said relay is not fused (maybe fusible link protected).

Confirm the fan functions normally by grounding those control outputs. Then once known, look at the inputs which give permission to run.
 
DET17 said:
All the relay needs to pull in your fan (presuming the fan motor is good, and relay is working, BOTH assumptions) is a ground path for the relay.

OP, check and see if your relay has near 0 ohms on the ground pin when checked back to the battery. Without that path, nothing happens. From memory, said relay is not fused (maybe fusible link protected).

Confirm the fan functions normally by grounding those control outputs. Then once known, look at the inputs which give permission to run.
Click to expand...
Fan runs normally, either by testing through the DTM or in use, i/e: when car is hot or in traffic. When the ambient temp is above say 30ish, the fan will not come on when the car is started and warming up, just when it's cold outside and I let the car idle for a minute the fan kicks in.
 
herbiedriver said:
Absolutely positive the AC switch is not on, that was my first thought, or even that I had something set for defrost, which on my VW it runs it through the AC circuit to dry the air. It only happens when the outside temp is below 30ish... AC works normally in the summer as well.
Click to expand...
Check to make sure the AC switch is really electrically off. I think it was possibly a 240 thing where this was common? But there's a chance the switch seems physically off but is still making connection.
 
The wiring diagrams will lead you to the truth. Not much new being discovered about these old Swedes.... the usual list of suspects will solve 99% of these riddles. The wildcard is bastardization by those who owned it before you.
 
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