i was told by a aircon expert that the newer aircon system does not use clutch system to engage the aircon when you turn on the aircon switch. Newer aircon systems goes by pressure,ie, once you on the aircon, there is a pressure pump inside the aircon compressor that activate the gas to flow. If the pressure pump is no longer as efficient, it will take a longer time to build up pressure in the system and this will delay the aircon 's function.
I was driving a c class and was told the pressure pump can be replaced at about $250.00
hope this helps.