Re[2]: A/C problems

[rdh@sli.com (Robert D. Houk)]

   My original posted problem: (1) a/c switch shuts off - light goes out and 
   switch position moves, but a/c continues to blow cold air and (2) off 
   position for blower still blows on low - will not shut off.

   There have been responses about the Electronic Climate Control System, but 
   unfortunately (or fortunately!) my 88 90Q has the standard/manual setup.  

Well, here's how the system works on my '83 UrQ: The temp lever when moved
to the right actuates a microswitch nestled into the "control head", which
is the master A/C "on" switch. Why they didn't just have a panel-mounted
switch to actuate the A/C even if in "heat" position is beyond me, but I
guess they know best, right? [Parenthetically, I will add that I now *do*
have a panel-switch to actuate the A/C w/heat so that I can defog as well
as defrost...works great!]

Anyways, this microswitch powers a relay (natch!) which powers

  1)	The compressor thermostat and relay
  2)	The Radiator fan high speed relay
  3)	The fresh air fan low speed tap

Your mechanical system is probably similar in concept. Several things to
try would be

  1)	disconnect the compressor clutch wire to verify that the compres-
	sor is truly running (engine should speed up/slow down noticeably
	as you manually dis/connect the compressor clutch; you can also
	hear/feel the compressor itself if you're in the engine compart-
	ment - they tend to have a pretty hefty "cycle" action).

  2)	trace the A/C switch wire to the relay, and see if it is still
	being energized disirregardless of the switch (or for that mat-
	ter, if the relay is simply stuck). The switch light may or may
	not switch on the same contact that the switch uses (i.e., the
	switch may be in the out position, which turns off the light,
	yet still "stuck on" wrt A/C wire.

  3)	pull the switch - physically remove the wire from the switch to
	make real sure it's "off" - measure and see if +12 is still some-
	how ("short") present on the wire, from somewhere downstream of
	the switch. (Be aware that the switch probably switchs +12 to the
	relay, but could be switching ground instead -- i.e, circuit could
	be +12 to relay to switch to ground; this of course makes trouble-
	shooting the circuit to *know* when and where voltages should
	be present sans a schematic something of a crap-shoot. Have spare
	fuses handy...)

  4)	pull the A/C relay (as mentioned on my car, there are "several"
	relays which cooperate to form the gestalt of "A/C") and make sure
	the clutch on the compressor releases, the blower fan shuts off,
	etc. and so forth.

I.e., in general, since you can't/won't buy the bentley, trace the wiring
and probe it as you go along until eventually the obvious bug is discovered.
I hope you're a contortionist (or have a good masseur/se handy...).

Good luck.

					-RDH