[Vwdiesel] TDI AC debugging

[James Hansen]

Electronics aside, every, and I mean EVERY a/c failure I have ever had 
has been the receiver dryer dessicant bag bursting, and dessicant beads 
going down the pipe to the expansion valve.  It takes almost nothing to 
futz up this valve, while still showing reasonably good numbers on 
gauges, as it's not a total plugging usually, just enough to make it not 
work.

Increased clutch wear is a symptom of this as well.

Hope it's something easy and plug-in.  flushing the dessicant beads out 
of an a/c system is a real PITA.  I now have a filter and pump for the 
job (using isopropal alcohol).  YOu oughta try this on a combine where 
the condensor and the evaporator are a mile apart...

-james


Val Christian wrote:
> Well, the furnace craps out on the coldest days of the year, so
> the auto AC should die on the hotest days.
> 
> Last night the bugs had a feast on my skin as I tried to find out why
> my 03 TDI ac died yesterday.
> 
> Symptoms:  System cooling anemic, topped off the R134a charge a couple 
> of weeks ago.  Worked better for a day then backed off in cooling power.
> Yesterday, total loss of cooling while running.
> 
> Diagnosis: Charge OK, by guages.  Compressor not engaging.  VAGCOM 
> apparently is of no help...the module for HVAC doesn't respond.  I
> assume that this car doesn't have one.  Pulled lower "skid plate"
> plastic, and measured power to compressor.  4.8 volts, sometimes 
> cycling quickly to 7.8 volts.  Since it's just a two wire connector,
> I assume that the power should be 12V when energizing the AC compressor
> clutch.  The somewhat worthless Bentley CD shows J293 (which other 
> literature calls the fan controller) as powering the clutch.  The Bentley
> CD also points me to a 13 relay cluster, which apparently my car lacks.
> I pulled lots of dash looking for it.  Apparently a vestige of a bygone
> era.  
> 
> So, it seems I may have a failed J293.  However, judging from a few posts
> (the forums on the Bentley website thus far seem to be the most useful)
> people have swapped J293 only to find that is not the problem.
> 
> Tonight, if I get home at a reasonable hour, I'll check out the 134a
> pressure sensor, which apparently drives the J293.  It's not clear to
> me why the voltage would be low and pulsed, going to the clutch.
> The clutch wear seems to be high, and I'm wondering if it did allot of 
> slipping in recent times.
> 
> Interim conclusion:  Still learning.  Bentley forums promise to be the
> most useful.  Manual is of marginal use.  Older, printed Bentley manuals
> are marginal in their usefulness on AC jobs.  Other manual vendors 
> for other vehicles have them beat.  My guess is that the J293 module,
> or the pressure sensor will be found the be the problem.  It is not
> clear to me how the ECM comes into play.
> 
> Any pointers are appreciated.
> 
> Val
> 
> 
> 
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