I had something quite similar on the 1997 C230. The AC worked great while moving at speed on the open road. However, once I got into town and slowed down, the AC compressor shut off. They system was still on and appeared fully functional. The problem was it blew only warm air.

The problem turned out to be a blown relay that controls the auxiliary cooling fan. Without the auxiliary cooling fan running and no air moving around, the compressor would shut off. I couldn't figure out the problem myself, but my mechanic figured it out pretty easily. It's worked perfectly ever since.

The relay in question isn't one of the normal ones you'd find in the fuse box area. Rather, it was somewhere in the cooling fan area under the front of the car.

I'd have to dig up the receipt to get the part number, but it was about $100 USD.

Best of luck.

__________________
Michael

1988 300 SL (5 Speed)
1994 E320 Wagon
1997 C230