A/C Compressor only works sometimes

My 90 Cherokees A/C compressor turns on most of the time,but not others. It works fantastic when the compressor kicks on but the rest of the time it just smells like mildew.
Ill explain my situation:

I was told there was no R-12 left in my system so I didnt technically evac it because I was told it was empty so I didnt figure it necessary.

I charged it with three cans of R-134a and it turned on most of the time but shakes the whole car and makes a horrid noise when its on.

I about three months after adding the R-134a added an oil charge to her and it quited down a little and turned on more frequently.

What are my best options here?

Is my compressor shot or does it just need to be evacced.

I will say when it was legitimately running on R-12 I only remember it being cold sometimes but that could've just been because it was running low.

Any help would be greatly appreciated its getting pretty hot here in Iowa.

You should have evacuated it. A refridgerant mix is unpredictable. You could try to evacuate it (with a vacuum pump) and start over. If you've already done damage, another try isn't going to cost you much.

I also have a 90 4.0 and just got my A/C fixed. I had to replace the comp., switch to R-134A, new drier (round black thing under comp.), and new expansion valve. I completely disassembled the entire system. Left the evaporator in the fire wall, flushed everything out with brake cleaner and blew out the lines with an air comp. Let everything sit for a while and dry, then replace all o-rings, added the oil to the new comp., and added the freon.

No leaks, but I still think it could be colder. I think I may be short on freon. I put in three cans, and I think I need about another half a can. Other than that, there are no leaks and it runs fine. There is a howling type noise coming from the front of the engine though. I have replaced the alternator, a/c comp., water pump, and idler pulley. It sounds as if it is coming from the power steering pump. It made this sound with the old comp. also. Belt tension seems to be fine. Thanks for any and all help guys.

90red

How cold is cold? Has anyone ever checked the air temp. coming out of the vents after the A/C's been on awhile and the interior air has gone thru a few changes. 55 degrees, 60, 65 or ???

I have never checked the temp coming out of the vents. I dont think its all that cold, but it does keep me from sweating to death if I keep it on MAX. It is definitely not as cold as my girlfriends 2001 Chevy Blazer. The air coming out of the Blazer is very cold. So cold, it can be over 100 outside and I can run it on normal on the second fan setting. I wish my A/C were that cold, but I dont think that will ever happen.

I was wondering, Is there a sensor or anything that tells the compressor to cycle? My compressor does not cycle, as far as I can tell. Thanks for any and all help.

90red