On a 1989 S4, my AC is not blowing cold air. The fuse is ok, and blower works. I am not getting power to the AC pressure switch. When I jump 12v to the compressor, I have cool air. All grounds seem ok.

Any ideas? Thanks!

David Hughes

 

See Steve's extensive electrical troubleshooting tips in this post:
<a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=14&t=002171&p=" target="_blank">http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=14&t=002171&p=</a>
<img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

 

I had a similar problem and it turned out that the wimpy relay on the control board in the console could not deliver enough current to engage the clutch. Measure the voltage across the clutch when it is supposed to be engaged. If it is only a few volts or less (but not zero), this may be your problem. My solution was a piggy-back relay arrangement like others have described.

 

Power to engage the A/C compressor clutch starts at fuse #6,
goes thru the controller,
out thru the wimpy relay,
thru the anti-freeze switch under the plastic shield at the base of the windshield,
thru the freon low-pressure switch on the receiver/dryer,
to the clutch.

Power can stop at any of these. Just use a meter or a test light to see where you lose the power.