Sorry if this has been dealt with in another thread - I don't know my way around here too well yet.

My 1991 190E 6 cyl. air conditioning works only part of the time. The unit's full, and according to my mechanic isn't leaking and is staying cold even when warm air is coming out of the vents. He's not familliar with Mercedes, but he's been doing AC work for years and he's from Las Vegas (so he should know his stuff). He thinks it might be a control unit of some sort. He also thinks the heater might be doing the same thing.

If anyone is familliar with this issue, I'd be really grateful. It's pretty hot here in Texas with no AC, and I like the car a lot. I'd hate to have to get rid of it.

The only other thing I can think to add is there doesn't look to be a pattern. Last summer, it seemed to do best if I drove for awhile before turning the air on. Now, it seems like it works better if I let it run awhile before hitting the road. I also haven't been driving it a lot this summer because of the heat.