My 1993 MBZ 300E's AC system is blowing hot air.

The local AC shop first pressure tested the system (no leak found) and added Freon. The system operated fine for about 3 days.

When I returned to the shop, the system was again pressure tested and again no leak was found and the system was diagnosed as fine. I was also told that the same amount of Freon was vacuumed from the system as was put in (supposedly confirming no leak). The system operated fine for about a week.

The AC tech is now telling me that my car's computer is sensing an operating or electrical problem and shutting down the AC (but the computer has not re-set now after 4 days). Does this make sense?

FYI, the car does have an after market alarm (which will be checked) and the head gasket was replaced about 2 months ago and the tensioner pulley was replaced about 6 months ago.