The problem may not be the circuit board. A common issue with window units is the settings. Once the ambient temperature reaches 100*F or higher it affects the cooling. If the unit can't reach the set temperature the compressor continues to run causing the evaporator to frost over. Turn the unit off until all the frost melts then turn it back on. As soon as you start seeing frost on the coils turn the control to a warmer temperature and see if the unit shuts off.
Thanks so much, sir. Yeah it had been a very humid day due to rain showers. I tried melting the ice with a hair dryer off and on for maybe an hour or so with the AC unplugged. Less than two hours later I tried plugging it back in but would immediately freeze up. It did this with the temp setting now changed to warmest temperature possible. So I kept unplugging it long enough to let it thaw out each time. And again it would begin freezing up once plugged back in.
Not sure if it’s a coincidence or not, but I finally took the front and top off the control panel this evening. The shiny, cylindrical shaped part is what I repeatedly tapped on with a screwdriver. Put everything back together and now it’s working correctly. Hope it stays this way.
The reason it frosts over so quickly is because there's saturated gas in the evaporator. Compressing any gas increases its temperature. The compressor pumps the compressed refrigerant into the condensor where it cools and condenses back to a liquid. When the ambient temp is high it doesn't condense completely and enters the evaporator as a saturated gas. Only the liquid refrigerant can boil off and that causes the frost because the evaporator is colder from the gas already there. When the system is turned off for a length of time the pressures will equalize. Now it won't immediately frost over until it's been running for a long time. If it starts to cycle on and off it won't frost over.
Well darn it!!! It was too good to be true. Came home yesterday to frozen AC again. It did it again early this morning. Any ideas, Rick?
On similar units in the past, the entire control panel had to be replaced to correct it. Fortunately one unit was still under warranty when it started freezing up. Tech came out then to diagnose and then order the control panel. But that was years ago.
Thanks so much Rick. I’ll see about ordering one. This AC had been stored in the garage here after the move. It was like new. Can’t recall the exact purchase date. Anyhow, had a different one in the dining room window up until maybe a couple weeks back or so. A severe thunderstorm moved into the area and lightning knocked out the power before I could turn off things. Once the power was restored a couple hours later, I tried plugging the other AC unit in and noticed there was a problem. The motor wouldn’t spin unless you hand spun it first.
That sounds like the start capacitor failed or is failing. The voltage surge after a power outage is usually what kills boards but lightning is a different story. You can get a big voltage spike going in just before the power goes out but it's not that common.
Just want to give an update. I held off on ordering part. So far all I have to do to remedy the problem is real simple. When compressor doesn’t cycle, unplug the cord, slide the unit partially forward and rap on the top of the box above the control panel with the side of a closed fist. Works every time. At least this is my cheap fix until the house sells.