On my 2000 Deville (base), I switched to AC OFF yesterday since it was a cool day and I just wanted the outside cool air inside the vehicle.

Apparently that was a mistake.

Today I went to use the A/C and I get nothing but warm air. I even checked to see if the A/C OFF switch was stuck on, but the display readout appears to be normal.
The A/C clutch is not engaging at all with the inside temp set to 60 (on up), but with the engine off the clutch still turns freely by hand.

Mind you, I have not had any issues whatsoever with the A/C or cooling temps, everything has been normal until today.

I also checked the a/c relay in the relay box under the hood and swapped it out with another identical(horn) relay and this has made no difference.

Also, no codes related to the A/C showed up either, just IPM B0429.
Which I believe is for the back seat controller which has never worked.
Went to the backseat and switched it to OFF, just to be certain that didn't effect anything also.

Any help is appreciated, thanks.

You're correct the B0429 won't cause this. It's indicating a problem with the actuator that sends air to the rear seats.

This is a long shot.... but try disconnecting the battery for 10 minutes and see if that will reset the HVAC module.

If the ambient air temp is below a certain degree, the AC compressor will not activate

If the ambient air temp is below a certain degree, the AC compressor will not activate
I believe that is somewhere around 35 degrees F.

It was 40dg F back when my system was R12.....

Yeah, that temp seems to fluctuate a bit with different years. Not sure why. Just to keep us guessing I suppose.

No luck after removing battery cable for 20 mins.

Would there be any problems if I removed the lower shield and ran a lead directly from 12v+ post at fuse/relay block to the a/c clutch connector?

Should I disconnect the connector or just back probe it?

Just want to see if the clutch kicks on, if not then it looks like I'll be ordering a new compressor & accumulator/dryer from rockauto.

I don't have guages to test the pressure in the lines, should I try to add some with the single hose kit and one can before I check the clutch with the hot lead wire?

thanks.

After doing some more online searches, I jumpered the 30 & 87 plugs using a paper clip with the a/c relay removed.
As soon as I installed the paperclip (w/ign off), there was a click. I turned ign on and a/c on at dash.

CLUTCH ENGAGES! It ran continuously for the 2 minutes I had it jumpered.
I attempted to cool the interior, but I get nothing but warm air still.
Happy that the clutch is operative, I shut it down and came back to post.

Questions:
Does this mean that the system just needs some r134a? I do not yet see any signs of a leak on lines, but I have yet to look at it from below.
Would I need to jumper the system again for the r134a to be added?
Also, why is the relay not opening? I'm assuming it's being told not to by the caddy's onboard system.

It sounds like you are low on refrigerant. You won't likely see any signs of a leak. Take it in and have it serviced. They can check the pressures and test for leaks with a dye or a sniffer. I would not just add refrigerant without knowing what you have in there.

Last night I added a can of r134a, the hose I have just has the guage at the can. After the can entered system it was at about 40psi on low side and I had cold air :) on passenger vents only.

After reading some older posts here, I see that this means that the system is still low on refrigerant. But I wanted to run the car today and let it mix in well during my daily commute.
By the end of the day, morning actually the passenger side was blowing warm air again...leaked out.

When I bought the r134a, I looked for a can of dye only, but didn't see anything but dye AND leak sealer combined.
I know that the sealer can add more problems so I didn't get any.

I may stop by NAPA tomorrow to see if they have any dye/leak detector only products.
Does anyone have any recommendations?

I do NOT just want to take it in and spend the time and money for some tech to send me on a wild goose hunt, unnecessarily replacing parts and charging for leak detection services. Especially since I know of no local reputable shops.
I'd rather find the leak myself, replace the source of leak and THEN have a a tech evac the system and add refrigerant.

All you can do is add a dye and charge it again. IF the leak is in the evaporator, you'll never see it. I'll need to rent a electronic sniffer to find that one. If it is leaking out overnight, it must be a pretty good (detectable) leak.