Fans problem - please help diagnose

[PranK]

Hi All,

I noticed a few weeks ago that my fans were not coming on, ever (which may account for part of my problem last year.)

First thing I did was unplug the thermo switch and bridge the terminals - both fans work well on high and low speed.

So, today I fit a new thermo switch as I was replacing my radiator at the same time. Well, no difference, neither of them come on. My feeble brain can only think of it being the switch still? I checked the fuse, made sure it was contacting and clean. I unplugged and re-plugged the fans in. Still nothing.

Is it likely to be the switch again? Or, is there likely to be another problem?

Thanks guys,

Christian

[JustCruisn]

Start here http://pics.tdiclub.com/data/516/A4_...ting_Rev_7.pdf


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[PranK]

So if I'm reading that right, a lack of ac pressure would stop low speed but would it affect high speed? My ac doesn't work so low pressure could be why.

Thanks for the link!

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[PranK]

Just reread, can't believe I missed this;

Low refrigerant pressure will lock out both fans and the AC clutch.

Ok, so can I bypass that check somehow to make certain it is a pressure switch?

[JustCruisn]

Sure looks like the AC will cause you to have issues.
Is the car overheating ?

What is wrong with the AC ?

[PranK]

Sure looks like the AC will cause you to have issues.
Is the car overheating ?

What is wrong with the AC ?

A/C hasn't been diagnosed. I'm not sure how to check the pressure in the system. (I'm still very much learning.) Up until now I didn't consider the A/C as being a critical component (ie, comfort only).

The car killed an oil cooler and sucked all oil into the cooling system last year. It was a hot day and I was in traffic. (My fans likely werent working either). My temp guage was bang on 90 but it was pretty hot in the bay, I'm assuming the sensor was faulty and I have already fitted a new one. So, the short answer to your question about over heating is - "probably".

[PranK]

Crap, I've just remember that I have a pressure switch fault code.

00792 - A/C Pressure Switch (F129)

So, I might replace that then next weekend and see if it helps.

[PranK]

Just got my pressure switch out. I'll order a new one.

Fingers crossed. (And thanks JustCruisn!)

[JustCruisn]

I have had the same pressure sensor error, the sensor was fine, the compressor was not activating as the field coil was stuffed.
The system gives a false negative as it is calling for the compressor to activate and it is not, so it then assumes the pressure switch must be bad as the pressure is not rising.

You could test the pressure switch, it uses a duty cycle value to indicate the pressure. But you would need the compressor running to raise the pressure so the pressure switch can see some variance.

You should be testing the compressor field coil.
It is easy:
1. Run the engine and turn on the ac, does the middle of the AC pulley spin ? NO - The coil is not activating
2. Unplug the electric connector and check the resistance over the 2 pins, open circuit means the coil is bad.

A new coil can be purchased without a new compressor. You can drop the compressor down and replace the coil and pulley.
About 2-3 hours depending on your skill level, does need the front end in the maintenance position to get clearance.
Years ago I got one from the UK for $200 delivered.
Pics of my experience

[PranK]

Oh great info, thanks for that!

Ok so I'll put the switch back in and test the coil. Am I looking for constant power or no power in the open circuit? (I'm assuming no power)

Timing is good as the whole front is off the car ATM for new radiator install.

Thanks again.

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