AlaskaPete

Hello Folks!

1999 A6/B5 2.8L (AHA), A/T 207K mileage

New to this car, bought with Problems.

NOW:
1. Aux Fan (electric fan, p/s of radiator) ALWAYS-ON HIGH immediately after Key ON. Shuts OFF again with KEY-OFF position.
SO FAR: [initially the Aux Fan didn't switch ON in any commanded function]
a. replaced Coolant Temp Sending Unit: behind intake, p/s near firewall.
b. replaced Thermo Fan Switch: lower right of radiator outlet.
c. replaced Fan Control Module.
*after replacing the fan control module it immediately switch ON HIGH at all times when KOEOff/KOERunning.

Some Forums suggest the A/C relay is 'Stuck Closed' on the 8-fold relay panel. This vehicle has the referred to panel, there just ARE NOT ANY RELAYS installed there. Pictures are included if I can upload. I'm referring to the panel directly behind the 13-fold relay panel.

I'm aware that these switches can be installed in either location, but I ordered and installed them separately, so unless these were installed incorrectly BEFORE I changed them I have no way of knowing.
a. p/n verified with NAPA
b. p/n verified again with Audi OEM catalog

I have the A/C high pressure switch on the way, in the event this failed which I have condemned because it was 'OPEN' when resistance testing it. [a/c lines have pressure, just don't know how much as I didn't measure at the time]

ps - the connector was OFF the switch, so I did plug it back in EVEN AFTER I condemned the unit as BAD.

WITHOUT THE A/C compressor Relay
and
WITHOUT the Fan Control Module Relay being; 1. identified, 2. located,

I'm at a loss as to where/how to proceed from here to get the AUX FAN to cycle ON/OFF when A/C is commanded ON/OFF, or ON/OFF when TEMP RISES and commands it ON. It is simply ON/RUNNING all the time.

The LAST TWO PICTURES are attempting to show NO RELAYS installed in the 8-panel relay bracket as information available tells me this is WHERE the Fan Control Module RELAY was supposed to be installed. None are present in the 2nd to last image as pictured, it is EMPTY.

ANY HELP/INPUT with identifying and location of these relays would be appreciated.

Thanks!
Pete

FrenchAvant

I can't help you with the relays, but the aircon HP switch is normally open (NO). It closes if the pressure is too high, which would usually be due to insufficient cooling of the condenser.

On my B5 the electric fan only runs when the aircon is operating. Normal cooling is by the "viscous fan" driven by the auxiliary belt via a viscous clutch.

The liquid in the clutch becomes more viscous ("thicker") as its temperature increases, so the clutch doesn't slip so much, resulting in the fan turning faster.

The fan can be turned quite easily when the engine is cold, and becomes stiffer when hot air flows over it from the radiator. Test it by running the engine until the fan is hot, then stopping engine and trying fan, or stopping fan with a rolled up newspaper when it is running. Some suggest a carrot to avoid damage to the fan, but fingers are not such a good idea.

You can also test it by heating the clutch gently with a heat gun.

FrenchAvant

In the last paragraph I should have you can test the fan by heating the clutch gently with a heat gun with the engine running.

This is because the clutch is engaged when a bimetallic strip on the front is heated by warm air from the radiator.

The bimetallic strip opens a valve, which allows the silicone fluid inside to flow from the reservoir in the centre, by centrifugal force, to the outside of the clutch assembly, which has vanes between the two parts, a bit like a torque convertor. This will only happen if the assembly is turning.

The fluid circulates between the reservoir and the outer part until the bimetallic strip cools and closes the valve again, so the fluid returning to the centre remains there.

Here is a nice graphic illustrating the operation.

AlaskaPete

thank you for the information.