[Vwdiesel] TDI AC debugging, Part 3

[Val Christian]

Gang,

At 7:55pm (they close at 8pm) I pulled into the local dealer and pickedup
the R134a refrigerant pressure sensor.  This is a three pin sensor, which 
provides a time variant signal indicating the pressure of the refrigerant.

Although I was told that an o-ring came with the sensor, when provided the
sensor, there was no o-ring.  So there were two transactions.

When I got home it was getting dark, and the bugs were hungry I got my
pastey white body changed into shorts, to give the bugs better access to
my tender flesh, and proceeded to change the sensor.

Tried firing the system up, and no dice.  No change in system behavior.

The next suspect component is the fan controller, and the link I
provided has testing procedures for the "j293" controller 
(VW 1J0919506K, Stribel, ~$150 dealer, less at other quality providers).

I haven't had the time (or enough remaining sacrificial flesh and blood)
to throughly check out the fan controller.  I may order one however, 
based upon some incomplete observations, combined with some level
of urgency, and lack to time to throughly ring out the existing controller.

Oh, the clutch will energize with 12V, and all indications are that 
the refrigerant loop is working fine.

In my mind, the remaining questions are:

	-the 32F temperature switch (probably not an issue)
	-the fan controller 
	-associated wiring and connectors (no observed salt damage)

I won't get home until about 11PM tonight, so I won't have time to do any
debug.  When I do, I will rule out the 32F switch/sensor.  And if I have
a controller in hand, I will swap it out. 

Unfortunately, this controller is not in a spot, nor of construction, 
where relays can be pulled, and jumpers put in place.  Where it's mounted, 
it is subject to engine compartment temperatures, etc.  And it appears
to be a solid state relay (electrical signal to clutch voltage measurements).
So I'm thinking electronics failure.

Getting back to the refrigerant pressure sensor I replaced...the old one looks
brand new.  No weeping of oil or staining.  So I've put it in my spares pile.
The dealer parts and mechanics all recognize the sensor (even the Nissan
guy said that VWs and Audis go through those sensors frequently).  So
that's something to file away.  

I hope this helps someone else down the road.

Val


















--- Val Christian <val at mongo.mongobird.com> wrote:

> Here's the latest thinking.  I found out in post:
> 
>
http://tech.bentleypublishers.com/thread.jspa?threadID=30762&tstart=105
> 
> 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.
> 
> Val
> 
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