How an HVAC System Works

• An HVAC system is a closed loop that uses a compressor to turn gaseous refrigerant to liquid and then push it through copper piping into the home and into the air handler (blower). Warm air from the house is sucked in through a filtered vent and pushed across the now chilled piping. The pipes turn the air cool and absorb the heat. The chilled air is blown though the home while the now warmed refrigerant turns gasseous and returns the compressor where the cycle is started all over again.
  
  

Freeze Points

• An HVAC system that is showing signs of freezing or frosting is not operating correctly. Two locations may show freezing. The easiest to spot is the copper pipe that exits the compressor (located outside the home) with cold refrigerant; this is the supply line. The second area, harder to access, is the copper coils that chill the warm air. These coils are located in the air handler, which is usually attached to or near the home's furnace. With the system running, remove the access panel and look for signs of freezing on the coils.
  
  

Causes of HVAC Freezing

• The main causes of freezing on an HVAC system are due to low refrigerant, a clogged air filter, a malfunctioning blower, dirty coils or operating your system in cold temperatures.
  
  

Signs of a Problem

• In addition to ice forming on the supply pipe, the copper pipe that heads into your home from the compressor, other signs of trouble include ice forming on the coils, condensation dripping from your secondary drain (located over a door or window), a full drain pan (near your air handler) or warm, humid air coming out of your vents when the system is on.
  
  

Problems You Can Fix Yourself

• The easiest fix is to replace the filters. These are usually found behind a vent in a wall or ceiling. Air filters collect dust and can clog up within a month. Highly clogged filters keep air from circulating over the coils leading to possible freezing. Dirty coils can be cleaned with a commercially available HVAC coil cleaner.
  
  

Time to Call a Professional

• If cleaning the coils and changing the filter do not stop the ice from forming, then it is time to call in an HVAC professional. A professional will check and replenish the unit's refrigerant levels and then run a systems check. Low refrigerant fails to move properly through the system and can collect in the pipes near the compressor unit. This pipe is "sweaty" under normal operations; but if the refrigerant is not moving, then it causes freezing. If there is freezing near the outdoor unit, chances are there is freezing along the coils as well. In either case, shut down the system and call a professional.