What Causes an Air Conditioner to Freeze?

Posted On: June 18, 2014

It seems ironic that in the summer heat, an air conditioner can freeze over. Unlike a heat pump, which is designed to thaw itself out when it freezes in the winter, an air conditioner is not built to handle ice forming on any of its components. So what causes an AC to freeze, and what do you do if you discover yours has frozen?

Reasons Air Conditioners Freeze

Refrigerant problems

An undercharged refrigerant system means the levels are too low. This can happen due to improper charging at installation or because a leak has developed. Either way, low refrigerant is not good for the evaporator coil, which becomes too cold when the pressure drops below normal. This allows moisture in the air around the evaporator coil to freeze and accumulate there.

Clogged air filter

This is a primary cause of low airflow, which results in less air being delivered to the evaporator coil for cooling. It’s important to keep enough hot air moving over the evaporator coil so it doesn’t freeze.

Closed or blocked registers

You may be tempted to shut the registers in unused rooms of your home, but if you shut more than one-fourth of the home’s supply registers, you could unintentionally restrict airflow and cause the AC to freeze. Rugs and furniture can also block registers and impair airflow.

Inadequate fan speed

The blower motor must operate on a high enough level that it sends air at the right speed over the evaporator coil. A too-low speed could result in insufficient airflow, and then you have a frozen AC on your hands.

Issues with the thermostat

The air conditioner could be running all night without your knowledge. This not only wastes energy, but since the air isn’t very hot, the constant operation with a mild air temperature could cause the unit to freeze.

Drainage problems

One of the jobs of the evaporator coil is to remove excess moisture from the air. Normally, moisture collects on the coils, drips into a condensate pan and drains to the outside. If something clogs the drain, backed-up water can freeze all the way up to the evaporator coil. The ice then further blocks the drain and exacerbates the drainage problem.

Improperly tilted window AC

If you cool your home with a window air conditioner, make sure the unit is tilted slightly down toward the outdoor half. This way, water can escape out the drainage hole instead of sticking around inside the unit where it could freeze.

What to Do if Your AC Freezes

  • Shut off the air conditioner to prevent risking damage to the compressor and wasting money.
  • Locate the condensate drain and make sure it isn’t backed up.
  • Speed up the thawing process by using a blow dryer on the evaporator coil. It’s also effective to run the AC fan without the compressor.
  • Consider opening up the ductwork to suction out water with a wet-dry shop vac as the ice melts.
  • Turn the AC back on only once the ice has melted and the condensate drain pan is clearly draining properly. The unit should begin cooling your home immediately.

AC Repair in Kansas City

While you can take steps on your own to prevent a frozen air conditioner (change the filter monthly, keep the supply vents open, inspect the condensate drain often and tilt the window AC correctly), other steps require a professional.

To have your air conditioner repaired, refrigerant level checked, fan speed increased, or thermostat adjusted, please contact Top Notch Heating, Cooling & Plumbing in Kansas City today. We take every precaution possible to prevent your AC from freezing over again.

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