Last spring we had a new Rheem HVAC system installed and it worked great all summer and winter. During the winter, the thermostat display did get zapped by static electricity, but the thermostat still worked fine. This spring, the AC unit was completely empty of freon. I called my plumber and he came out and pressurized the system with 200 psi of nitrogen for 5 hours and there were no leaks and no drop in pressure. He recharged the system with freon. Now, the ac runs constantly. It only cools the house to 75. It is able to maintain 75 even when its 95 outside, but it won't go any lower than that. The AC unit has literally been running constantly for days. I have gone outside and felt the lines coming into the house. If I turn the system off for a while and then turn it back on, the cooling line gets very cold, but after an hour, it is warm again. My plumber can't seem to figure out the problem. He suspects it is the thermal expansion valve, but is waiting for a confirmation call from Rheem to confirm his suspisions.
Any help would be greatly appreciated.

Last spring we had a new Rheem HVAC system installed and it worked great all summer and winter. During the winter, the thermostat display did get zapped by static electricity, but the thermostat still worked fine. This spring, the AC unit was completely empty of freon. I called my plumber and he came out and pressurized the system with 200 psi of nitrogen for 5 hours and there were no leaks and no drop in pressure. He recharged the system with freon. Now, the ac runs constantly. It only cools the house to 75. It is able to maintain 75 even when its 95 outside, but it won't go any lower than that. The AC unit has literally been running constantly for days. I have gone outside and felt the lines coming into the house. If I turn the system off for a while and then turn it back on, the cooling line gets very cold, but after an hour, it is warm again. My plumber can't seem to figure out the problem. He suspects it is the thermal expansion valve, but is waiting for a confirmation call from Rheem to confirm his suspisions.
Any help would be greatly appreciated.


It is able to maintain 75 even when its 95 outside

20 degree split is good.

Now here are a few possibility's. Since the refrigerant mysteriously escaped the unit as you stated there has to be a leak or someone released the refrigerant since it just does not disappear on its own. Next since the unit was without pressure it allowed moisture into the system. R-410A refrigerant uses a oil for system lubrication that just loves to suck up water like a magnet to metal. This moisture can do great damage to the system unless the plumber that you called installed a drier in the liquid line before he recharged the system with R-410A refrigerant. Also the water that is in the system could also play a roll in the malfunction of the expansion valve. The expansion valve can and will cause the water in the system to freeze at the point of expansion at the valve causing all kinds of system problems you are experiencing.

The system may need to be really dried out well and that means it could take a couple of drier changes along with deep vacuum's from a quality pump to remove the moisture. This will take a quality minded service technician to get the job done correctly. Since I have not and will not be there I am going by your description in your post to try and figure out the problem. Good luck.