Yesterday I noticed that the a/c wasn't blowing cold air any more. I went out side and the unit was off. I've messed around with it and I can get the unit to turn on and work just fine when I manually press in on the contact switch. I replaced the contact switch but still having the same issue. Any thoughts on what to try next?

Hello I have a Heil propane furnace with a Goodman 2 ton SEER 13 FREON unit. It's new. I turn on the AC and it blows cool for a while, then just blows room temperature air. The thick, insulated copper piping that comes off the outside condenser is cold and wet when it runs, but after a while it goes warm to the touch as the AC stops cooling. The installation company has been out a couple times to look at it. First time they said it was the wire mesh filter somewhere, next time he said he overcharged it and that's what caused it to shut off as time went on as a safety feature to not damaging the unit. So now a few days after their latest call, my problem is it cools for a while then goes back to not cooling and the copper piping stops being cold. This is the upstairs unit. The downstairs, with the exact same setup, cools like a champ. It's a brand new air filter in both. Let me also add that when I put my hand over my outside units, warm air is coming from the one downstairs that works well. The upstairs unit, that works poorly, only gives me cool air from the fan on the outside unit, which tells me that it isn't getting warm. Advice is appreciated, thanks in advance!