AC works for 20 minutes
 

Okay guys, please give me your ideas. 1996 civic, AC works great for about 30 minutes in the morning when it's cool and for about 15 minutes in the afternoon when I leave work. It does not go out all at once, I will feel the air temp slowly drop and then sometimes the AC will come on again but sometimes it wont and when it finally stops, it blows hot air. If I park the car for a few hours, the AC starts working again. Today once it had totally gone out and was blowing hot air only I looked at the clutch is not spinning. I think it is either the ac clutch or possibly the relay. Thoughts?

AC quits working
 

This sounds as though it could be a bad expansion valve allowing the unit to freeze over. When the AC quits working you can look under the hood, to the compressor, and determine if the clutch is engaged. If you are uncertain what to look at during this test, have someone turn the AC on and off while you are looking at the front of the compressor during that first 30 minutes when everything is working correctly. If, after 30 minutes, the compressor and clutch still engage then it would indicate moisture in your system and a potential expansion valve failure. Was your system repaired? Is it possible that a new dryer was not put in during that repair? That residual moisture could be causing a failure at the expansion valve, or, it has contaminated that small orifice with rust due to the system not being evacuated correctly, with a new dryer installed after the system had been opened to atmosphere.

Hope this helps. You can look on how it works sites to see the operation of air conditioning for further clarifications.

Ed Fisher
Dallas