I've searched and found nothing related to this problem.....hopefully someone can give me a starting point.

A/c works....and blows cold.....but then the cold goes away and it is blowing regular temp air........then the cold comes back. It cycles like that as you drive......
At first I thought it was ok at idle......but it doesn't matter what speed....or whether you are accelerating or not.....although......it does "seem" to do better if you are just maintaining a speed.

I've tightened the belt( relatively new and no cracks)......and checked the pressure in the system. Pressure reads about 30 psi (in the blue on the guage which means it doesn't need freon)(using a charging guage and can of freon kit from Advance)

Previous owner had it converted to 134 and had some repairs done to it before I bought it.

It's an 85 with the 4.3 v6.

No problems with changing from dash vent output to defrost output and back.......as long as I turn it off between changes.

Any suggestions will be appreciated........Thanks.

Maybe a vacume leak in the little diaphrams under the dash on the passenger side.

Do you have a way to see if they hold vacume?

Also check the vacume hoses and connections on the back of the AC controls

The system could be freezing up(evaporator) which will cause the hot air condition, after it thaws out will blow cold for awhile until it happens again. If the system was opened up for repairs and recharged without drawing it down on a vacumn pump for at least 30 minutes then you probably have moisture in the system.

Check Expansion Valve per your manual. Check Engagement Coil for weak compressor clutch which could occasionally disengage.

Also, FYI, here is a pretty good A/C Q&A site. Hope this is of some help. Let us know.

http://www.2carpros.com/topics/ac.htm

Take care.

Finally found the culprit........Besides having two small vacuum leaks under the hood........My fan clutch was worn out. The fan wasn't turning fast enough and it caused the freon to overheat......it was reading 300......and should have been down around 200. That caused the compressor to cycle on and off very quickly........faster than I have ever seen one do it.
New fan clutch and everything seems to be working ok now.
Just wanted to thank all of you and give anyone else a heads-up on checking that clutch if they are experiencing any A/C problems.

Bob