[200q20v] Overeager A/C

Bernie Benz b.m.benz at prodigy.net
Sun Oct 21 08:58:39 EDT 2001


You were not specific enough in describing the symptoms.  Does the
compressor run all the time or not?  Because of the frosting of the
compressor suction line (yes or no?) I suspect that such is the case.  The
probable cause would be failure of the clutch suppression diode in the AC
relay.  Two failure modes for this diode. 1. The more common, diode failing
open causes the electrical system voltage spike upon clutch dropout, the
radio pop.  2. The diode failing  shorted allows power to the clutch all the
time with ign on.  BTDT with both.  The solutions are to either replace the
AC relay, $$$, or open it up and just replace the diode, $0.15 @ Radio
Shack.  The diode is one of the two black axial lead diodes at the base of
the relay, cover removed.  The the supression diode is the one across the
relay contacts.  Replace it with a 50V, 2A or better diode.


> From: Kneale Brownson <knotnook at traverse.com>
> Date: Sun, 21 Oct 2001 00:13:06 -0400
> To: v8 at audifans.com
> Cc: 200q20v at audifans.com
> Subject: [200q20v] Overeager A/C
> Air temperature tonight is ~40 degrees F, and my  A/C  on my wife's V8
> doesn't want to shut off.   We were travelling far enough for the car to
> warm up on the ECON setting, and as I pulled into the drive, I could hear a
> slight repetitive squeak, so I left the engine idling and opened the door,
> allowing me to hear a sound sort of like a cross between a leaf in the fan
> and a bad bearing squeaking.  Sped up with increased engine speed.  So I
> opened the hood and found the A/C plumbing right at the front all
> frosted.  I tried cycling through LO and HI temp settings with the system
> set to AUTO just to see if maybe the A/C clutch got hung up.  It blows cold
> air out the center vent on LO and warm air out the footwell and dash
> openings when switched to HI, but the noise persists.
> What do I look for tomorrow?   Is it likely the A/C clutch fried in the
> "on" position?  I noticed the electric fan wasn't running while I had it
> set to ECON, but I didn't check when I had it set to AUTO.
> TIA.

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