<E34> AC Failure - Request for Advice

["Brant M. Miller" <brant@xxxxxxxxxxxxxx>]

My 1995 525i with 49,350 miles on the odometer  just turned its air
conditioning on without request from me.  We were driving along in 75 deg=
F
weather with the air ventilation blower operating at level 2.  The green
indicator lights on both the AC and the air recirculation switches were o=
ut
as they should be.  At the start of the trip, only fresh air was being
provided.  But then the vents began to emit cold air.  Upon arrival at ou=
r
destination, I looked under the hood.  The refrigerant return line to the=

AC compressor had a layer of white ice on it - moisture frozen out of the=

air.  I tested the AC controls.  The green indicator lights turned on whe=
n
the AC and recirculation switches were activated and turned off when
deactivated.  I left the car for about a half hour.  When I restarted the=

car, all seemed to function normally.

Probably non-related information: when activated, the AC compressor or
something near it emits clattering noise - the sort of sound that I would=

expect to hear from bits of metal on an old car banging against each othe=
r
due to rough-idle vibration.

My friendly dealer has agreed to look at the car on Thursday, but since
this is obviously an intermittent problem and since the warranty is about=

to expire, I would appreciate some advice.  Two technical questions,
electrical and mechanical, and one business question.

A.  I've spent some time with the Electronic Troubleshooting Manual.  As =
I
see the electrical situation: =


1.  The the on/off switches with the little green lights are incorporated=

in a Switching Unit.  =

2.  All connections to (and from) the Switching Unit lead to the Integrat=
ed
Climate Regulation Control Module.
3.  Both the Climate Regulation Control Module and the B8y Pressure Switc=
h
provide AC-related information to the Engine Control Module (DME).
4.  The Engine Control Module activates the Air Conditioning Compressor
Relay.
5.  When the AC Compressor is switched on, the air ventilation system blo=
ws
cold air.

So, either the Switching Unit, the Integrated Climate Regulation Control
Module, the pressure switch, the Engine Control Module, the Air
Conditioning Compressor Relay, or the wiring must contain an intermittent=

defect.  Or have I missed something??

In any event, working the issue does not look like a job for a guy with a=

volt-ohm meter!  If voltage and resistance levels are in the ETM, I have
not found them.  And I would expect the Modules to be mega-buck items.  B=
ut
if you know of  things to check, please let me know.

B.  It seems to me that when the AC is working correctly, the refrigerant=

line from the evaporator/expansion valve to the compressor operates above=

32 degF and does not condense and freeze moisture on its outer surface. =

I've looked at both the Bentley Service Manual and the Bosch Automotive
Handbook.  They do not contain such information.  Anybody know for sure. =

And if such freezing is not normal, what does it indicate?  Failed
expansion valve with excessive circulation of refrigerant??

C.  Finally, and probably most importantly, if my dealer is unable to
locate and correct the problem on Thursday, what do I need to do to ensur=
e
that my warranty does not expire before the problem is corrected?  Do I
file some sort of description of the problem with BMW NA or what?  Do I
need a statement of the situation from my dealer?

Any help that anyone can provide on any of the above will be most
appreciated.

Brant Miller

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