CT Rob

My '89 S4 runs noticeably hotter with the A/C on -- how should I diagnose the issue?

Thanks!

-Smitty

Bilal928S4

When you turn the AC on, do both your fans come on?

Randy V

When the AC is turned on it should activate the second fan.

There are several threads in the archives on how to troubleshoot and repair this.

CT Rob

Thanks! I will check.

-Smitty

Bilal928S4

If you are stuck you can bring it here and we can both look at it. I have a little bit of experience on these cars.

WallyP

"When the AC is turned on it should activate the second fan."

Both fans should always run at the same speeds.

RKD in OKC

On my 95 the box selection to recirculate A/C turns on fans with key on even without car started.

Mrmerlin

get the IR gun out and verify your readings with and without the A/C engaged./

69gaugeman

The car can run hotter with the A/C on as you are removing heat and passing it past the coolant radiator. It also depends on what you mean by noticeably. Mine moves about a needle width hotter on a day where the ambient is around 35 Celsius.

Also radiator efficiency can be reduced by many factors and as the coolant system becomes less efficient the A/c heat will cause a general rise in temperature.

CT Rob

The A/C doesn't seem to have any immediate effect on the second fan. I searched a bit but didn't find the specific article(s).

SeanR

Wally is right, hitting the A/C on will activate these no matter what the temp is. They will just be on low and once the engine heat increases the rate of the fan rpm will also increase.

Bertrand Daoust

Like Wally said.

Both fan always run together on my car.
They start when the engine is warm enough or when the AC is turned on.

rbrtmchl

I didn't see it mentioned, but to see the fans running when the hood is open, you will need to depress the switch on the hood line along the passenger side fender to simulate the hood being closed. I think this is a safety feature to prevent the fans from running when the hood is open.

Bertrand Daoust

Bob,

On my car, a '91 S4 too, with the engine running, the fans will come on with the hood open without touching the switch.
If the fans are still running after turning the engine off, which does happen very, very rarely, they will stop as soon as the hood is open. Unless you depress the switch like you mention.

CT Rob

Looks like the passenger side fan is not coming on -- what do you suggest?

Thanks!

-Robert