• Frost on an air conditioner may mean more serious problems inside the unit.air conditioner vent image by Tammy Mobley from Fotolia.com
  
  Frost anywhere on an air conditioning unit may mean it is time for a repair. In most cases, the frost is caused by something restricting the airflow that moves through the unit. However, the cause of that restriction can stem from several different sources, ranging from fan motor problems to air conditioning parts that need to be cleaned.
  
  

Dirty unit parts

• Dirty air conditioner parts can cause frost to build up on the unit, according to Air Filters by OxyClean. A dust-clogged air filter, for example, can prevent air from properly flowing through the unit, therefore causing frost to build up. A cooling coil that is dirty also may prevent air from flowing through the unit. To see if a coil is dirty, remove the filter and check the coil, which is located behind the filter. Use a mirror to check under the coil, where frost may occur. Other obstructions could cause air flow problems. If you are experiencing this, check the return grill on the air conditioning unit to make sure nothing is obstructing the air from entering the unit.
  
  

Freon problems

• If frost is building up on an air conditioning unit, the system itself may be low on freon. Freon is a type of coolant that decreases the temperature of the air that runs through the air conditioning unit. If the unit is low on freon, the coils inside may freeze. Check first for any disruptions, and then turn off the unit, allowing the frost to thaw. If the frost returns once the unit is turned back on, a licensed air conditioner repair technician will be able to conduct tests to determine if the level of freon in the unit is up to correct levels.
  
  

Fan motor problems

• A bad fan motor may disrupt airflow and cause frost to form on the air conditioning unit. If a problem exists with the motor, it may appear overheated. Air Filters by OxyClean recommends checking to see whether the motor fan turns off after it is overworked by setting your thermostat to the function of "fan on." If the motor turns off after 30 minutes or so, the motor may be damaged. This will cause frost to build up because the air conditioning system will work harder to cool the building, causing the system to malfunction. A technician or contractor should be called to assess the problem further.