My A/C has started having problems.

When it was hot (90+ F) and I was running the A/C high it would stop blowing cold air after 20 minutes and start blowing warm. It would blow cold at low levels and if it was cool outside. The compressor would be off and after about 2 min. I would turn on the A/C and the compressor would kick back on and run but for less than the original time it ran from a cold startup.

The service rep and dealer thought it was the compressor super switch sensor but after finding out it was 2000 he said it was fixed in 1998 and that wasn't the problem and the problem was a leak. So I took it home and planned on recharging it myself but when I hooked up my gage it said it was 45 psi and I just assumed not to mess with it and took it back to the dealer.

The next day he called me and told me my evaporator had a leak and was low on R134 and that it needed to be fixed. So after probing him, I told him to go ahead. He replaced the evaporator and I picked it and I was having the same problem. I took it back to him and now he tells me the clutch is worn on the compressor and that is the cause of it.

So, am I getting the wool pulled over my head? Could either of these problems cause this issue, independently? Why would the clutch not work when the temperature is elevated?