Overheating and AC problem

2000 Acura Integra GS 1.8L DOHC not VTEC 128,000 miles.

OK. My Integra just started acting strangely. I noticed that the AC is only blowing cold at 1800 RPM or lower and that the temperature gauge will climb up to around 3/4 when within the same RPM's. When driving, the AC will only blow regular air (I can actually feel the AC shut off) above 1800 RPM's and the temperature gauge will stay around 1/2 to 5/8. If I'm just sitting and idling, the car gets hot (or at least the temp gauge climbs). When I rev the engine, the temp gauge will drop. I've not let the temp gauge climb higher than 3/4, so I don't know if it's actually overheating. The cooling fans run fine.

This is weird for me. I'm used to older cars and I could understand how the fan being driven by the engine would cool at higher RPM's, but I don't see how this would make much of a difference on a newer car.

Sorry for the essay and thanks, in advance, for your help and consideration.