Climate Control

Compressor Functions Intermittently

Rex McIntosh wrote:
>
> Can someone tell me where the temp switch is that cuases the compressor to cycle
> on and off?
>
> Every thing else in the chain seems to be fine, but some times the airson
> compressor just will not go!

Rex:
After having my TB tensioned by the dealer last Spring, my A/C compressor would not
engage. The same week I attended a Tech session sponsored by Potomac PCA, and the
master mechanic for the sponsoring dealership identified the culprit; a bad connection at the
male(red wire)/female(black wire) plugs for the compressor circuit found in front of engine on
passenger side (in front of cover for TB). The mechnaic explained that this is fairly common
after a TB tension/replacement. If you've had a recent tensioning, I'd give this connection a
look. You might want to check it anyway for corrosion.

Regards,
Joe Rausa '89S4


The diagnostic for this runs from testing at the connector to the clutch itself, through the
connector at the side/top of the radiator sheet, then at the pressure switch on the dryer.

The temp switch is located at the top of engine compartment, under the plastic "rain shield" at
the base of the windscreen. On my '89, the switch is retained by an aluminum angle bracket
right about the center of the car, has two spade connectors, and has the probe capillary tube
running to the left (american driver's side) a few inches before it drops into the evaporator
housing.

FWIW, I went through a similar diagnosis on mine early last summer. Low freon gas level will
sometimes cause erratic operation of the compressor, and is related to ambient air temp as
much as anything if the level is just right.

My gas level was OK, and the problem ended up being a defective relay on the climate
control module in the center console. The relay on the controller from the factory is
underspec'd for the clutch coil's load. I did a little 'field engineering change' that adds an
external relay. If you find that the coil voltage is OK when the coil is not attached, yet drops
when the coil is plugged in, check for that same symptom when measuing at the terminals on
the thermal freeze switch. If you have low voltage under load at that switch, you are a
candidate for a new console controller or the dr's external relay fix.

Here is a downloadable diagram of the modification, with
instructions. You can view it and print it out using Adobe's Acrobat Reader. If you do not
have this common program installed on your computer you can get a free copy directly from
Adobe

dr bob