[Vwdiesel] TDI AC debugging, Part 2

Val Christian val at mongo.mongobird.com
Tue Jun 26 11:05:10 EDT 2007

Here's the latest thinking.  I found out in post:


That pressing the AC button causes the controller to see if the pressure
is OK on the sensor.  If the pressure is OK, and the ambient temp is OK,
then the fan goes high, and the compressor fires up.

Since the fan doesn't go on high, and the compressor doesn't fire up,
I'm thinking the pressure sensor is bad.  

Sure, it could be the temp switch, or some other things.  The low pulsed
voltage measured on the compressor clutch could just be stuff a high 
impedance meter is seeing on a solid state controller.

Testing the pressure sensor is not direct, since it is not a switch, but
rather a duty cycle sensor, like an o2 sensor on a gasser exhaust.
The VW parts guy says they do a couple of these sensors a month in the
summer (two yesterday).  So from a "shotgun" standpoint, it's a possible
shot in the dark.

Furthermore, the sensor simply screws on, and does not require an
evac/recharge.  So it's easy to try.  And eventually, I'll probably
have one go bad.  Since it senses both low and high pressure, it's not
a something I can jumper to easily test out.

Part 1K0959126B, $53.50 from dealer.  I'm having the parts place
next to work see if they can get it for me.

If this is it, I can drive home in cool comfort.  I'm not that optimistic.

If anyone is faced with this problem, the above Bentley link has a procedure
for checking out each function on J293.  If I swap the pressure switch, and
that doesn't work, I'll be doing the checklist.

I'll post when I know more.


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