There are a number of factors that weigh in to why an AC unit’s inside handler would freeze up, most of which are best handled by a professional HVAC installer and repair service. While it is possible to fix this problem on your own, breaking just one coil on the unit will result in a much ore costly repair job. Here are a few things that can cause the unit to freeze, all of which are preventable with a bit of preventive maintenance.

Dirty Air Filter
A dirty filter restricts air flow and can cause condensation to form on the coils. Once that happens, all the moisture in the air will be attracted to the cold and the unit will quickly freeze over. It will generally take 24-48 hours for the unit to dry out when that happens, unless you switch over to heat in an effort to speed the process. During the heat of summer, however, chances are waiting it out will be preferred to making the house even hotter. Clean the filter and watch for re-freezing.

Low Refrigerant
If there is a leak in the refrigerant line, the refrigerant will not remain charged. There may be a weak solder joint, a breach in one of the valves or some of the piping rubbing against another part of the unit causing friction. The list of ways a unit can leak is extensive. Depending on the age of the system, sometimes it is less expensive to replace than to repair. Newer units are also more energy efficient which will save you money over time.

Dirty Evaporator Coil
The evaporator coil will always collect dirt over time. That is why it’s so important to keep up with cleaning it. Once it gets dirty, air flow becomes restricted and that leads to the handler freezing up. You will likely notice a difference in cooling capability right away so when that happens, the evaporator coil is a good place to start checking for problems. Unfortunately, though, at that point a good cleaning will probably not solve the problem. Call in a good tech and consider it a lesson learned.

Defective Relay or Blower Motor
If the blower motor isn’t running at the proper speed, this will compromise the cooling ability of the unit and lead to a freeze up. The speed of the motor fluctuates, generally slowing down once it heats up. The relay could also cause intermittent problems with starting. This is not a consumer-serviceable part so call a trusted technician for help.

Chances are you won’t be able to fully diagnose the problem on your own. The best first course of action is to simply let the unit thaw and completely dry out. Forcing it to dry using hair dryers or high-wattage light bulbs may be something your neighbor recommends, but these things can cause more problems in the long run. Always consult with a licensed professional when problems like this one arise.

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