Air Conditioner Freeze-up



When the Average Joe thinks of HVAC issues or concerns, the first things that usually come to mind are clanging furnaces, thermostat malfunctions, or filter replacements. What we don’t realize, unless we’ve had the misfortune of going through it ourselves, is that a sizable portion of technician service calls has to do with frozen air conditioner condensers. It actually looks like a small glacier is emerging from your lawn and engulfing the outdoor portion of your air conditioning unit. It seems as if it should defy logic - it’s a sweltering summer day and yet the condenser resembles an outdoor ice-maker. But, without delving into thermodynamic technical talk, a frozen A.C. is the natural byproduct of an evaporator coil freezing up. What exactly causes this evaporator coil malfunction can be chalked-up to a couple of likely culprits.

However, before we dredge into the details of causation, should you find that your condenser is iced-over, immediately turn off the air conditioner and let it defrost completely. After enough time has elapsed and the system is totally ice-free you can attempt to diagnose the cause. The usual suspects responsible are scant in number but can range in scope.

Insufficient Airflow

This means that air from your home, as it’s routed over the evaporator coil (which is housed in the indoor portion of a typical central air system), is decreased in amount and/or hindered somewhere. That is, not enough hot air is reaching the coil, generating a drop in refrigerant temperature that’s below freezing. Commonplace items of concern are:

Dirty Air Filter - if you’re not changing the air filter at least every 90 days you run the risk of debris build-up on the filter which can seriously obstruct airflow.

Blocked Returns - oftentimes furniture or curtains can stymie air meant to flow onto the evaporator coil.

Closed Vents - people mistakenly shut vents in unoccupied rooms unaware this creates undue pressure on the system, thereby forcing it to work harder. It also lessens the amount of cool air expelled and can initiate air duct leakage.

Deficient Blower Motor - In this case, airflow is obviously decreased. If so, it’s imperative you contact a professional HVAC technician.

Clogged or Leaky Ducts - Airflow is either inhibited or diverted out of circulation. This usually requires special equipment to recognize and best left to pros.

Dirty Evaporator Coil - This is not a do-it-yourself fix. A contractor will need to remove the coil and then clean it with (potentially) hazardous solvents.

Low Refrigerant

Assuming that an HVAC system was installed properly and is functioning accordingly, it should never lose refrigerant. Refrigerant is like a conveyor belt that moves heat from within the home to be discharged outside. The only means by which a shipshape apparatus loses refrigerant is via leakage. Pinpointing and repairing leaks is the domain of professional techs. Proper protocol must be followed when handling and disposing of these sometimes toxic chemicals.

Air conditioners are designed to operate within a specific temperature range, and it’s imperative that when the mercury falls below 62℉ outdoors A.C. operations cease. At this temperature, internal system pressure drops organically and is prone to spearhead freeze-up.


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