Questions about cooling fans fcm and thermo switch

So I have a new to me A6 4.2l sedan. I recently completed the transmission rebuild. I noticed that while driving A/C blows warm. I read ALOT about possible problems. I noticed that neither fan ever turned on. I checked both with 12v directly to them. Pass side outward pusher worked, driver side inwards puller didn't. I bought a replacement so I know both work.

I have read considerable about the fan control module being suspect. I bought a used (supposedly tested good) replacement. I know that fan control unit gets battery voltage after relays and fuses. I tested and my fcm is getting like 13v with car running at its power plug. Each of the two fan outputs from the fcm are putting out 11v when car is hot , coolant at like 200°f. No fans running. Now if I jumper the four pin thermo switch from the lower radiator hose, both fans run on low and high.

My questions are...

1. At what coolant temp (in °f) should the aux cooling fan turn on.?
2. If I jumped the terminals to simulate a closed thermo switch, and the fans came on, doesn't that tell me my fcm is good and the switch is bad?
3. Could someone test a known good fcm? I'm curious if 11v at idle normal output for the fan leads.

Hope this made sense.

Fear not the Diy!
Bratcop

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Rich81 said:

Also have A.C. problems on my 4.2. I had voltage to my fan but fan was dead. Basically the fan should come on with your A.C. switching between econ mode will stop the fan. It would be worth seeing if there's any fault codes for the A.C., as this may disable the fan during A.C. use. You've jumped the switch so you know you fan controller is good and the fan itself. So perhaps if engine was hot enough it would come on as expected but because of some other A.C. fault it doesn't come on when a.c. activated?

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I will swap in the old original head unit tonight to see if that helps. I think the replacement hvac unit was from an allroad, non v8 so it may be different from a cooling standpoint... Idk

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Rich81 said:

If you have access to vag-com/vcds there are a lot of measuring blocks you can monitor on the hvac that point you in right direction. I have a list of them all I can share if needed.

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Trying to get this thing buttoned up without dropping the couple hundred on that software, so I don't have it at this point... Just torque obd

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