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2001 Mazda Protege AC issues

I have recently been having quite a few engine issues with my 2001 Mazda Protege. Currently what is happening is that while the car is running, at idle, the heat sensor on the dash starts to rise (indicating that the engine is getting hot) and the air conditioning turns off (the air coming through the vents is ambient temperature). While the car is in gear and in motion this is not an issue and the faster the car is going (freeway vs side streets) the colder the air. I am trying to figure out why this is happening, what might fix it, and about how much the fix will cost. Other pertinent information:

- the thermostat is only 3 months old (has about 3000 miles on it)

- the radiator is only 3 months old (again, about 3000 miles on it)

- the AC system was charged when the radiator was replaced, but due to overcharge the compressor would seize; this problem was corrected about 2 months ago and the compressor has not been seizing since

The problem described above has only been happening for the past week. I was informed that the thermostat would cycle on and off while the car was being operated in extreem heat. I currently drive the car in Houston TX where temperatures have been consistently in the 90s since June and the problem only started a week ago and happens regardless of the temperature outside (75 - 100 degrees, regardless).

Any tips, hints, or ideas would be useful! Thank you!

Make sure the radiator cooling fans are operating whenever the A/C is on. If the fans are not operating (even on an erratic basis) the A/C system pressure will climb and cause overheating.

What you were told about a thermostat cycling is pretty hokey and adding that to this alleged system overcharge it sounds to me like whoever is doing this work probably should not be.
At this point there’s not enough specifics known to make an accurate guess but do make sure those fans are operating.

I did check the fan as soon as I could. While the temperature on the engine was rising I opened up the hood and checked - the fan indeed was running. (This, of course, was done on a safe spot off of the road and while the car was in park - but the temp was still rising).

The person who overcharged the AC has not touched the car since. I brought it to a different mechanic (hightly recommended; excellent reviews) who diagnosed that problem (also, not the same person that had mentioned the thermostat cycling).

I’m out of ideas for what would simultaneously affect the engine temp/air conditioning while the car is at idle. Any other thoughts? Thanks for the help!