Either the A/C compressor clutch slipped or the polyvbelt slipped causing the protective circuitry to disengage the compressor. Basically, if the logic circuit (which compares compressor speed with engine speed and was installled in various iterations including a Klima control relay, MAS control relay and others) determines slippage it will disengage the compressor for approx. 2 minutes. It will then engage the compressor again and if slippage is detected again it will lock out the compressor until the ignition key is cycled off. This is MB's way of protecting the polyvbelt from destruction should the compressor lock but it results in lots of instances where the compressor will not operate. There are other posts on this site about this. Mark