A frozen evaporator coil is one of the most common issues for air conditioners and heat pumps during the cooling season.

If you have a frozen evaporator coil, shut off your system immediately as prolonged operation can and will damage the compressor. Shut the air conditioner off at the thermostat and-if you are positive the fan is running – turn the fan switch to the “on” position.  This will keep the blower fan on and will assist in thawing the evaporator coil and provide some cooling as the ice melts. (If unsure the fan is running keep switch on auto.)

The coil freezes due to the temperature of the coil is below 32° F which causes the humidity/condensate to freeze.  There a many reasons an evaporator or AC coil will freeze.  The most common are:

• Dirty Air Filter
  • Check the air filter to ensure it is clean.  If not, change it.

• Lack of refrigerant or a low refrigerant charge is also a symptom of a frozen evaporator coil.  Contact SunBay Air Conditioning to re-charge.
  • If the system is low on refrigerant there is a leak.  Most older air conditioning systems will lose their refrigerant charge.
  • Many times a re-charge will result in proper operation for the season.
  • We will discuss this with you when we do the re-charge.

• Dirty evaporator coil

• Blocked air return grilles.
  • There are instances where a low placed cold air return grille is blocked by a piece of furniture and this restricts the air flow.
    • Remove any restrictions and allow the evaporator coil to thaw prior to starting operation again.

• Too many supply registers that are blocked or shut off.
  • There are instances where a home owner has shut off too many in order to force air to one part of a home.  The rule of thumb for most homes is each register provides around 80 CFM to 100 CFM of air flow.  Each tonnage of air conditioning requires 350 CFM to 400 CFM.  If you have a 2 Ton air conditioner, then you require 800 CFM of air flow.  If you have 12 vents in the home, you need at least 8 to 10 of them unrestricted.

• Blower motor not operating at full speed or not at all.

• A stuck or welded shut contactor will keep the outdoor unit running all the time.
  • Without the indoor unit blower motor in operation there is no air flow and the evaporator coil can freeze.