Why does an AC freeze, I have broken this down into 4 categories that's easier to remember
#1 most likely cause is AIRFLOW!!!!!!!!!!!!! not enough AIR FLOW! AIRFLOW IS IMPORTANT!!!
This can be Dirty Evaporator coil, dirty filter, restrictive or undersized filter, dirty blower wheel, blower motor on the wrong speed, bad blower motor, blower capacitor, bad blower relay or motor wiring.
It can be ductwork such as return air blocked, return air crushed or undersized. It can also be supply duct crushed undersized, dampers closed, or grill registers closed. Insulation blocking the ducts or blower or anything else you can think of to not allow enough airflow across the evaporator coil.
1A Stuck contactor falls under this as the contactor sticks and keep the unit running when the airflow stops.
#2 Mechanical restriction. clogged filter drier, kink, valve partially closed, clogged screen, undersized metering device a TXV stuck closed and more.
#3 Temperature to low, Indoor temperature is to low (low load) or the outdoor temperature is too low
#4 least likely is Low on refrigerant. This will cause frost at the metering device but it also reduces capacity. it is possible but it take a long time at the right humidity conditions. However it is misdiagnosed as the main cause because adding refrigerant causes the pressures to go up and out of the freezing range. without solving the root cause adding charge just floods the evaporator and gets more liquid to the compressor.
Bryan Orr has a great article with the same topic with a different view point that may help
hvacrschool.com/ac-systems-fr...
23 июл 2024
