Airconditioner Control Unit Problem, Please Help

[DSTANTSTAR]

1988 S4 5-speed
My mechanic diagnosed that the relay on the control unit is bad but does not want to fix it. I found a fix using a RadioShack relay. How do I remove the control unit from the consul? I cannot remove the knobs from the sliders. I tried pulling with my ahnds and also with a plier, no luck, any thoughts? what am I doing wrong?
thanks

[stepson]

There is a black surround going around the radio and the AC head unit. Very carefully and gently pry the thin places from the console and then you can carefully, gently and gingerly remove the surround. You will see 4 small phillips screws holding the AC head unit. Undo those as well as the 2 small phillips holding the AC button unit. It's usually easiest to remove the small AC button thingie at the same time as you remove the AC head unit.

You will not need to remove the knobs or the sliders for the fix you describe. Unless you are pretty good with electronics, I would recommend sending the unit off for rebuild.

[Mrmerlin]

Ok to remove the HVAC head unit first remove the center vent slats,
it slides to the back of the car.
Then carefully slide the H trim up about 1/4 inch and then pry one of the top edges out then remove the trim.
Once this is done you will see the screws that attach the HVAC unit and the AC switch plate to the console remove all 6 of these screws and the washers.
NOTE a small magnet will be needed to prevent losing the washers and screws.
Once this is done then slide out both the HVAC head and the AC switch panel,
mark the connectors to aid in refitting.
Once you have the connectors of the HVAC head there are two of them then you can remove the screws that hold it together and carefully press the snap fittings apart with a small pair of pliers.

NOTE the screws lengths are different so pay attention to where they go.
Once the covers are remove then you can see the relay on the board a search should bring up a detailed process to swap out the relay and install the Radio Shack part.

NOTE Disconnect the battery before removing the HVAC unit.

NOTE dont pull on the knobs of the HVAC unit as they will be damaged and thus require new sliders to be installed

[JK McDonald]

Hey Dstantstar, You should also consider installing an additional relay into the A/C clutch circuit to help extend the life of the small relay behind the dash control unit. On some 928’s the current draw through the small original relay can eventually cause them to fail. But - if you place the coil circuit of a “fog light” style relay as the load for the smaller relay and then direct a separate 12 volt power source through the fog light relay contacts to the A/C clutch, the smaller relay will virtually last forever.

On both my 928’s I simply mounted the fog light relay near the B+ jumper post found on the right hand wheel well. Then I connected the wire that originally went to the A/C clutch to the fog light relay coil. Add a jumper from the B+ power post to the primary input contact of the fog light relay. The final jumper is from the output of the fog light relay to the A/C clutch itself. To be on the protective (safe) side I added in a 5 amp cartridge fuse between the B+ post and the A/C clutch coil.

There are a couple of good write-ups on this topic under compressor relay -
928 Tips

Good Luck, Michael