Civic - Honda :: Temp Gauge Go Up And A/C Blows Hot Humid Air

i have a 2002 Honda Civic EX, 155,000 miles. I've been having this problem for quite some time and the mechanic has not been able to figure out what the problem is. He has changed the thermostat, pressure tested the coolant (or something along those lines) but the problem persists. The mechanic also pressure tested the radiator system and said there was no leak. He also told me the tank was overfilled with water, apparently I didn't need to be waiting for the car to cool down so I could add more water, so I've stopped doing that. I have NOT had the scheduled 150,000 maintenance done yet. The mechanic said it wasn't 'urgent' and if I wanted to wait I could. I was hoping to spend the money repairing this problem before doing that, which he said sounded OK to him. The timing belt was replaced in 2007 right before I moved across the country.

I'll try to be succinct, but the explanation is long. Overall: when driving the car to run errands around town the temp gauge used to quickly go all the way to HOT & the A/C starts blowing hot/humid air. When this happened I was pulling over, turning off A/C & radio & putting the car in neutral until the gauge goes back down, used to take only a few minutes but if driving in town (stop lights/traffic) i have to keep doing this b/c the needle returns to the top quickly. I also started trying putting the car in neutral while stopped at lights or in traffic & if i pushed on the gas pedal & kept the engine at 3K RPM the needle would go back down & A/C would start blowing cold when I started driving again.

The other part of this is if i change the A/C vent diverter from all vents blowing at upper body to vents blowing at face & feet or all vents blowing at feet the green 'recycled air' light goes out & the air starts blowing hot & humid, this persists even if I push the 'recycle' air button again.

Until yesterday this temp gauge & A/C issue has not been nearly as much of a problem when driving on the highway at a consistent speed, in other words when the car doesn't have to idle the problem didn't occur very often, the temp gauge may have moved towards 'HOT' but never got all the way up there. Until yesterday. I had to drive thru town with quite a bit of construction & resulting traffic as well as a few stop lights which sent the gauge go to HOT quickly. When I got on the highway I was expecting the gauge to go back down & the A/C to start blowing cold air.... alas, it did not. the gauge stayed very near HOT the whole time & the A/C never blew cold air. It was 106*F yesterday?

And yet another part of this problem, which the mechanics have told me is NOT related to this problem: in the winter time the heater took an extraordinarily long time to heat up and then would only blow warm air while the car was moving at a pretty high speed, under around 30 MPH and there was no heat, and definitely no heat when idling. I do not remember the temp gauge hanging out at HOT all the time but I do think it would go higher than the middle range.

The car has yet to actually overheat. Apparently the mechanic can't diagnose/repair the problem until the engine DOES overheat, at least this is what he has told me. I'm not feeling very confident in this mechanic, as clearly the problem is getting worse over time. And I don't believe it is OK to continue driving a car when the temp gauge is at HOT all the time, that doesn't seem smart at all. Sadly, the mechanic that used to work on my car & was able to diagnose & repair problems quickly & competently has gone to work somewhere else & is no longer working on cars. So, I have decided I cannot continue to use the current mechanic and am now faced with having to take it to the dealership, something I REALLY hate to do. I just don't know of any other reputable Honda repair folks in the area & am tired of being w/o my car for days at a time and still have to deal with the problem.