For those of you who live in the Phoenix area during the summer, you rarely experience a day in which the temperature drops below 99 degrees. Average high temperature for June is 104, July is 106, August is 104, and September is 100. The last thing you want to hear is a dripping sound of a leak, one indicator that that your air conditioner has frozen.
It is worth explaining how an air conditioner actually works. There is a principle in thermodynamics called the Joule-Thompson Effect. It states that if other factors are kept constant, as a gas expands, its pressure and the temperature decrease; if compressed, the temperature will increase. Your unit works by having the evaporator coil expand refrigerant inside of it, causing rapid cooling of the coil. As the cooled coil comes into contact with the air inside your home, the refrigerant absorbs this hot air. The now heated refrigerant is conveyed outside your home where it is compressed which causes it to heat up and shift the heat that was inside of your home to the outside atmosphere.
Your air conditioner freezes because something has changed this process causing your evaporator coil to cool more than it should. Possible causes for this are as follows:
- Insufficient air flow across the evaporator coil causes it to freeze. If your air conditioner is not blowing the inside air over the evaporator coil, the heat transfer cannot happen and the refrigerant which should be removing the home warmth, is not.
- If there is a low level of refrigerant in your air conditioner, then your unit can freeze up because of the lower pressure inside the system. In this situation, your unit has inadequate refrigerant inside it, but it is being forced to expand to the same amount. This expansion has a cooling effect. As your evaporator coil drops below the freezing point, the humidity in the air will freeze when it comes into contact with the coil, which causes it to ice up.
- Mechanical failures. If you have a clogged filter dryer, an improperly functioning blower fan, dirty coils, or a twist in your refrigerant lines, these factors can alter your system’s pressure and cause your air conditioner to freeze up.
Other causes could include a poorly maintained air conditioner, dust storms, and proximate trees causing leaves to accumulate inside your unit.
What Should You Do When Your Air Conditioner Freezes
- Turn the unit completely OFF—don’t try to thaw the unit by adjusting the thermostat upward.
- Check your air conditioner’s refrigerant level. Add more if necessary.
- Check the airflow to see that it is not obstructed. If necessary, replace the furnace or any filters.
- Check your evaporator coil. A dirty coil can cause a lack of airflow across it, causing your air conditioner to freeze.
- Check any restrictions in air flow from the duct work. Open the vents in your ceiling and check for any disconnections, bends, or leaks. This may involve a trip to your attic.
- Check for extremely dirty duct work. Having the duct work redone is recommended over trying to clean it yourself.
- Schedule preventive maintenance. Click here to see a 49-point checklist.
Hopefully by following these steps, you can avoid that awful moment when your air conditioner freezes up during those summer scorchers.
