Hvacdoc

I have an 05 Tahoe that has a leaking shrader core. Last year I put in a can of R-134 and tightened down that cap real good and it worked great.
Yesterday, I went to turn the air on again for the 1st time. ( I should mention I have a 3 zone climate control system in this truck.)
I unscrewed the cap and heard hissing so I knew it still had some but not enough to engage thee compressor, so I added 2 small cans and that got the compressor to engage but short cycle. I then proceeded with a third, and then a 4th can. Every time the compressor engages, The gagues pull down low and it continues to short cycle. I am getting cool air, but something else is going on I believe. I don't want to just keep pumping it full of refrigerant unless you think that 4 small cans isn't enough for this truck. I should mention that I had all 3 zones calling for 60 degrees with the fan on high and recirculating cabin air.
Besides replacing the bad Schrader core, can you guys think of anything that I should look into before taking it to the shop later Monday morning?
Thanks in advance for your time, advice, expetise, and help!
Respectfully,
David B
Hvacdoc1@hotmail.com
Palmyra, Pa 17078

73shark

Welcome to the forum.

First you should have a set of refrigerant gauges to accurately charge your system. You need to know the amount of a full charge by weight also. That information used to be on a decal above the radiator. Not sure it still is. To get accurate readings, you should have a fan blowing into the grill. It's hard to diagnose the problem without knowing what the high and low pressures are.