A/C diesel problem

[Redfar]

Hello,
I have a Mercedes w201 190 2.5 diesel.As the hot days are coming,I checked the A/C system of the car.When I turn on the a/c it starts working fine but after a few minutes it cuts off,and never turns on again.I checked the Freon(mine is on R12)and it's reading fine.When the A/C was working it cools properly so I think the compressor is doing his work when it's working.I think it's something from electrics.
I take off the relay (near the battery) for a few seconds and when I put it back the A/C starts again(reset),not for too long.and I repeted this for few times but it stills shut off after a few minutes.
Does any one experience this problem,from where I have to start checking the electric components?
Thanks