2001 Yukon denali XL A/C Problems

[KAKALAK]

So I found a leak in the schrader valve in my yukon. Spent 9 bucks for a new one. bought 4 20 oz cans. filled it up and it was working. Left the car idle in the driveway and got the fam ready. Went back out and it was just blowing hot air. The ac sticker on the yukon is wore so i couldnt see the capacity. So I was like maybe it needs more freon. Bought 2 more 20 oz cans and it worked again. But the next day I get in and it does the same thing. My wife drove it to the store and said that she heard a hissing noise. I popped the hood found the other schrader valve to be leaking. I talked to GM and they said that they replace those valves regularly. But I think its leaking because I may have over charged it. But it is tempormental, it seems, gets cold for a minute and then back to warm air. The cycle repeats itself. And I have the auto climate control turned off during all this.
Took it to aamco for their free AC check and went no where for free. Waste of time besides them saying I need to replace everything. Go figure

It seems to blow cold air when the engine is 2000 rpms but at idle it doesnt. I know I have a leak now but these symptoms were present before it leaked.
I bought it used and had the same problem but the dealer put 3 cans in the system and it worked for awhile. Thats what led up to me replacing the 1st schrader valve.

anybody have these problems before.

Its got: 115K miles, and has moderate stumble while idling after 1st starting it up. I also thought since the idle was messing up it may not have been letting the compressor spin fast enough, but I am kind of stuck on it right now. Im hoping to fix it myself if I can find out more from you guys

 

[ScottyBoy]

I have a 2001 Burban with the rear air. The capacity on mine is 48oz. I put 4 12oz. cans in mine.

 

[KAKALAK]

I have a 2001 Burban with the rear air. The capacity on mine is 48oz. I put 4 12oz. cans in mine.

thanks for the info, I guess I overcharged it