Crazy A/C in 300E

I bought a very clean '88 300E from my mechanic when the weather was cooler. Part of the deal was that he would fix the non-working A/C. I am pretty sure that he put a compressor on a that time. It worked pretty well, but had a slow freon leak. He found it in the manifold. In order to save money, we had an A/C parts shop repair (weld?) the manifold instead of buying a new one from MB. No more leak.

In warm weather the A/C seems fine, and the car can get quite cold. However, when it gets into the high 90's and higher, the vents will blow cold air for about the first 10 minutes and then hot-humid air for 2 minutes then back to cool air. It seems like the compressor is turning it's self on and off. The hotter it is out side, the shorter the time it blows cold. It may cycle back and forth or just give up and blow hot air.

It is driving me crazy and I am sure my mechanic is tired of all the free labor.

Mark R. Potter