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My cooling fans seem to not come on at the right temps/intervals. I dont think they need to run with outside temps in the teens and cruising the interstate. They do come on with the a/c on. temp gauge in dash has not worked/most of the time for a long time. I removed the connector and jumped across the terminals and verified that the low and hi speed fans and relays work. Am i correct in the assumption that the instrument gauge is fed by the same switch as controls the fans? bottom of radiator. From what i read the sensor below the intake hose is just for the ecm. I also read that removing the sensor from the radiator can lead to the plastic radiator breaking and leaking afterwards. has anyone done this repair and has any advice?

Rusty Spokes

The A/C will allow the fans to run..no matter what the engine temperature is. The idea is to have air flow over the A/C condenser with the A/C on. The exception is when it gets very cold outside. There is a sensor to disable the A/C compressor when it is too cold outside to avoid damaging the A/C compressor.

The radiator fan switch and temp gauge are not connected. Two independent systems. There is a another sensor for the temp gauge and the fan switch sensor...

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Yes, i understand why the fans come on when the a/c is turned on.
My question is about replacing the fan switch and temp gauge sender and or verifying their operation. I do have a multimeter to use.
Also i am wondering how brittle the radiator might be. Has anyone replaced this switch and do you have advice?

Rusty Spokes

I've replaced many of the radiator fan switches over the years. I doubt your radiator will suffer if you remove and install a new fan switch. The radiator has a brass fitting that the fan switch threads into. No problems there.

The temp gauge sender (if we are talking a 12v 2.8 V6) is on the coolant pipe passenger side behind the engine. Tight location but changing out the sender is easy enough. The Bentley has a graph with a temp to resistance curve.

See the link and scroll down to:Coolant Temperature Gauge-Overheat Warning: Multi-Function Temperature Sensor (MFTS)

SJM Autotechnik, Audi Technical Service Repair Information

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That was easy....the temp sender for the gauge was just a matter of removing the intake pipe and plastic housing. disconnected the iac connector, used a 29mm (i think) injector socket. I never even drained the coolant. Remove sender, inserted the new one and only lost maybe a quart of coolant. I then went to the cooling fan switch on the radiator. This one was even easier. It was barely tight. I loosened it up from above, with the new switch in the same hand removed to old one and swapped. very little coolant loss- maybe 2 cups.
Both units were original '93 Now my temp gauge works and the cooling fans come on at a good temp. The new switch is set a bit colder than the original. That's ok. The temp sender was the original 4 prong that they do not make anymore. Connector very briddle.