Electric fan issue driving me crazy.... Need an expert.

[cashmancab]

Car is 95 M3. I removed the engine fan and aux fan and installed the SPAL Puller fan (track car). I also used the Z3 lower temp Radiator thermo switch. I Did NOT used the relay switch they sell for this conversion. I used the existing relay already in the car. I don't understand the need for the extra relay if one already exists (I still don't understand the need for the relay even though it may be the cause of my issue). I wired the fan to the 80C wire only. I did not hook up both 80C and 88C because this is a single speed fan.

Here we go:
If I jump the plug - The fan works.
I test the thermo switch to verify it is coming on - That has been verified.
If I run an extension wires from the plug to the thermo switch pins - the fan works.
When I plug the plug into the thermo switch....NOTHING....WTF.

So I made the assumption I must have a bad PIN in the plug (Only thing that makes sense to me), So I ordered a used plug off EBAY. I get the exact same result.

So either both plugs are bad. Or Both plugs are good and I have no idea whats going on. Again, I did not use the "relay kit" but I can get the fan to activate using the cars existing relay. It's only when I plug them together that it doesn't work as a system.

My next option is going to be to run a hard manual switch. Any issues doing that If I cant figure this out.

Edit: One more bit of information. When I was trouble shooting. I plugged the plug into the old original thermo switch and used a torch to heat it up. The fan turned on as expected. I did the test again a couple minutes later and nothing... That is why I thought I had a bad pin connection. It worked once, then not the second time.

[pbonsalb]

The radiator switch provides grounds to turn on the relays. I think that when high speed is triggered low speed turns off. With your single speed fan you may need to bridge the switch wires so aground remains to turn on the fan. One of the lower temp switches people use does not always fit right — you have to remove a retaining tab and then it may not stay in place. I would plug a spare switch into the harness and heat it up and check the fuses, relays and power outputs and ground.

[cashmancab]

"I think that when high speed is triggered low speed turns off" ----- I did a pretest before I wired everything up and found when the high speed side kicked on, the low speed remained active. That's why I figured I didn't need to wire both since the low speed remained active in both conditions. Each wire sends 12V to the fan. I'm not an electrician but I'm assuming the OEM fan has a second winding which increases the fan speed when the second 12V activates (high speed).

"I would plug a spare switch into the harness and heat it up and check the fuses, relays and power outputs and ground".------- I did the spare test (mentioned in the original post). It worked correctly once but I couldn't duplicate it again.

[pbonsalb]

When I ran a single speed fan, I bridged the grounds and the power wires. I don’t know if you must do that, but I did. If you can figure out exactly how the relays work, maybe you could just connect the low temp switch wire to the high speed relay trigger.

[cashmancab]

I twisted the high speed and low speed wires together at the fan plug. Everything is now working as it should (at least based on tonights test). I would love someone to explain this to me. I really thought they were independent circuits.

Only thing different is I twisted the high speed an low speed together at the fan and replaced the Plug at the fan.

Thanks for the inspiration pbonsalb.

[RRSperry]

I'll go take a look at the ETM and see...

Ok, after consulting the book of electrical knowledge, He's what I got.

On the temp switch, pin 1 is ground, 2 is low speed, and 3 is high speed. All they do is ground the relay and the relay passes the high current to the fan.

The AUX fan is two motors in a single housing. Both are independent.

Turning on the AC grounds the high speed relay and energizes the high speed motor. The AC can cycle the compressor on and off which will cause the fan to cycle, either between high and low, (if the low temp is active, or off if it's below the setpoint.)

So... You only needed to use one pin of the temp switch to make the fan run. Grounding both wires (for a single trigger) shouldn't be a problem,but doesn't seem necessary.

But, the fan isn't getting 12V from the temp switch, that should be from the relay. You are just triggering the relay with the switch. If you get what I mean...