AC Clutch Always Engaged With Air On

Hey guys, I own a 1996 Supercharged 3800.  I just recently replaced the clutch and accumulator as well as the orifice tube, the PSPump lines, water pump, heater hoses, all pulleys and the belt tensioners.  I've been working on cars as a hobby for a while and my dad has been a refrigeration tech for his entire life (I'm 37 BTW).

I followed the FSM in replacing the components.  I check in the FSM searching for "clutch" and found it was only supposed to be engaged either in defrost or AC modes.  I only see the rear defrost, windshield, and Temperature (up and down); there is no general "defrost" (nor "AC") button, but I am guessing that is what "Windshield" is. There is one button left of the rear defrost that is worn out so I can't tell what it is. Is that "Recirculation" to only use cabin air?

Anyways I am cleaning out the cooling system with some cleaner and with the heat on I noticed the Accumulator sweating cold bullets of AC.  Then I saw the AC clutch was engaged.  it only turns off if I completely shut off all air.  I am guessing this is not how this is supposed to work?

I also noticed a few intermittent times the AC turned off and switched to heat mid drive, I am wondering if that key-panel is getting ready to kick the bucket.

Is that panel a replaceable thing?

Stay tuned, I'm going to make a write up on replacing the MF switch with another non-discontinued GM version.  =D

I realized there is another button, "Vent", and pressing it turns the compressor off. I searched the FSM for Vent Button and found that the button directly below it that is worn out is the "Recirc" button. It specifically mentions that Vent will shut off the compressor but there is no mention about the compressor for Recirc.

Make sure your refrigerant charge is correct (not just operable; the A/C is pretty tolerant actually - don't overcharge and don't run it low on refrigerant. And *never* add any "sealer."). Hint to me is the sweating accumulator. Whether it sweats at all just depends. Check the charge to ensure that's not the cause (it probably isn't but we'll see).

If you are in "auto" mode the AC compressor will run most of the time, to dehumidify the air, even with the heat on, until the outdoor ambient is cold enough where the evap coils would freeze over and block airflow. This also cleans the cabin air to a certain extent by laminar flow over the wet coils, the moisture traps dusts. At least, it traps the small dusts very, very well... Temp is controlled by the blend doors.

That said... I've run my A/C in Auto mode for two decades+. No compressor rebuilds, just topping up refrigerant (with a gauge) every so many years (original hoses) has been the only repair of note. Had the system flushed and refilled once. Running it keeps the seals good, apparently.

The general defrost button is (supposed to be) the one on the upper right. The rear defogger, lower right. WINDSHIELD is the display indicator that will light when you're running front defrost, or if you've set the controls to blow air of whatever temp onto the windshield.

That HVAC control deck was new for 1996 model year; consider getting one pulled from a newer car, IIRC the control strategy is better in the later ones, but don't take my word for it. When you have the HVAC control out, you will see that the button panel comes off the control assembly without fuss or damage. Also, eventually the control deck will need the resistors replaced (they all do). When you remove the button panel most likely you will see the PC board under the resistors is toasted a bit. There is a write-up on this site about how to do that repair, and on repairing the lights for the buttons.

Looking forward to your write-up on replacing the MF switch.

Albertj