Auxiliary Cooling Fan Operation

9014 Views 4 Replies 4 Participants Last post by V6er, Nov 6, 2012

TFOOLULU

Discussion Starter · Nov 5, 2012

2003 Passat Wagon 2.8L V6. Replaced auxiliary cooling fan (electric) and thermo switch on lower radiator hose outlet. Old fan totally inopertive with 12V direct to fan plug terminals. New fan op-checked with 12V direct OK. Unable to determine high-low speed jumper settings at old-new thermo switch to check high-low operation. New fan runs only when engine and a/c is turned on...it does not run when the ignition (only) and a/c is on...nor does the fan run after turning engine off at operating temperature. Also, appears that fan only operates at one speed while the engine is turned on and at operating temperature. Believe that the remainder of fan circuit goes through the aux fan control unit under the bumper and then back to the fan relay under the dash. QUESTION(s): Is the fan variable speed? Is the fan supposed to operate when the engine is not running and the a/c is on? If the fan is variable speed, is the aux fan control unit or fan relay the most likely culprit?

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FrescoGreen01.5

· #2 · Nov 5, 2012

Everything you describe is normal. The fan does not run with the engine off, by design.

It runs on low speed with the A/C on, or if the engine coolant temperature gets too high. It only runs on high if the coolant temperature gets higher (another temperature switch) or the A/C refrigerant pressure gets higher (typically in hot weather). Mine will switch to high speed on a hot day in a stuffy garage, or at a red light, but not this time of year--you might have a little better luck with your climate.

But if it runs on low (as you describe), it will probably run on high when needed. On low, the fans runs in series with a resistor (in the aux fan control unit); on high, it runs directly on 12 volts.

BTW, there is an electric coolant pump on the V6 (only) that runs after the ignition is turned off if the coolant temperature is high enough.

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V6er

· #3 · Nov 5, 2012

There is no fan relay on your car. That is a 1.9 device.
The fan speeds are controlled by your AUX fan control module.
It operates at 2 speeds, low and high

12v for high and apx 8v for low.
So applying 12v directly will jump it directly to high speed.
The fan will only run when the engine is running and the A/C is on.

In some situations the fan will continue to run for a short while after engine shut down. Ie high temp.

I have the v6 coolant fan control / wiring diagrams on pdf if your interested.

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broomhandle

· #4 · Nov 5, 2012

i had this issue as well. its normal for the fan. i think it just sucks, and is really loud. im also getting a low buzzing/hum from the fan when it shuts off, and it stays buzzing for awhile.

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V6er

· #5 · Nov 6, 2012

broomhandle said:
i had this issue as well. its normal for the fan. i think it just sucks, and is really loud. im also getting a low buzzing/hum from the fan when it shuts off, and it stays buzzing for awhile.

I do not think that's normal.

That low buzzing / hum you mention sounds like the fan trying to turn at it's low speed but cannot for some reason. Maybe partially siezed.
does it spin freely/smoothly by hand?
If not swap it out. Only takes 30 mins and simple tools.

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