E30 Aux fan not run

[Ohme30]

It only run A/C on
I test jumper wire form dual switch high and low speed. it fan not run

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I hear the relay work only

[superj]

it only runs when the ac is on, not when temp geos over a certain level. and you tested it by jumping the wire at the temp sensors on the radiator? which model car is it? a 325i?

[Ohme30]

Yes. It E30 coupe 318i m40 b18. Model in Thailand

[superj]

you have two sensors on the radiator? one high, one low? and when you jump one set of wires, or the other set, not at the same time, nothing happens on the fan? but it works when the ac button is pushed?

[Ohme30]

Yes. I have two sensors high and low. But work only a/c button is pushed.

[superj]

And when you put a jumper wire, you tried one plug and then separately tried the other plug? Not together?

And the relay turns on when you jump each plug?

I would imagine you have a wiring issue but i will have to check my manual when i get home

[Ohme30]

Ok. I'll take the car to check at the garage. Thank you so much👍😊

[superj]

Ok, here is pics from the bentley20200208_103305.jpg20200208_103255.jpg

[Jimkden]

On some models the fan has 2 speeds. The low speed circuit has a load resistor located on one of the fan supports. Remove the driver side grill. The load resistor has a heat sink on it. Later cars have a larger heat sink so they don't overheat and burnout. Check with a ohm meter across the load resistor, it is probably burned out. If you can, get a load resistor from an E36 and wire it in place of the old one. I bought a car with one burned out and made this replacement.

[Ohme30]

Thank you 👍

[doctorx69]

about the load resistor... quick question. I bypassed my last year for ac. After charging, the ac would blow cold, but only when going down the road. In stop and go driving it would blow hot. I jumpered around the load resistor and changed the fuse to a 30. Worked like a charm. The ac was cold again. My question, is it ok to keep it like this?