A/C randomly quits

I did have a mobile tech come out and check it out. He took off the thermostat, inspected the wires that go into the thermostat, and noted that the wires had bare wire showing for about 1/2 inch before going into the unit. There were 7 wires, I think. Several of them had burn marks. He cut the wires back, stripped them and reinstalled so that there is no bare wire showing (the insulation goes right up to where the wire connects now). That was two days ago. Yesterday we were gone all day and sure enough it cut out while we were gone again. I can get a replacement thermostat for like $30. I think I will just replace it. He thought that maybe moisture got on the wires, but I'm thinking if moisture got on the wires, it got inside the unit too, so there's got to be something still shorting out or not right within.