The way your air conditioner works is by absorbing heat from the air within your home. As the refrigerant evaporates within the indoor condenser unit, the evaporator coil absorbs heat from the air blowing over that coil, but if the air filter is too dirty, then warm air is restricted, which can cause the coil to freeze.
This is a problem for two reasons—a frozen coil can’t absorb heat, first off. This causes low airflow which is inefficient and costly. In addition, as the ice thaws, the condensation will have nowhere to go but into your property.
A frozen evaporator coil can actually have a couple different causes aside from a clogged air filter. So if you do notice this problem, you should call an HVAC pro regardless of whether or not you suspect your air filter is to blame. Trying to thaw the evaporator coil on your own could cause further damage, or you may injure yourself.
This problem doesn’t just afflict central air conditioners either—it’s troublesome for heat pumps as well. And since you use your heat pump for cooling and heating, you’ll want to take care of the problem ASAP, before you need it to remain in heating mode for months at a time.