Image of evaporator coil with ice formed on the bottom thrid

Evaporator Freezing

Frozen evaporators are a common problem with air conditioning systems. A typical evaporator coil will run at 40°F/4°C, if the coil temperature drops to 32°F/0°C, the coil will start to freeze. This reduces the efficiency of the system and can damage the equipment.  The evaporator can freeze and then thaw, when the compressor cycles off, so there may be no indication of a problem until the day you really need it.

When the load increases on an air conditioning system on hot summer days, it is not uncommon for the compressors to run continuously. If the coil is below freezing and with no off cycle,  the ice will build up on the coil as shown here.

On split AC systems, you may not be able to see the evaporator coil but you can see the copper piping.  If ice is forming on the suction line, it means the coil is likely to freeze. If the line is insulated, then pull back a little bit of the insulation to expose the pipe and see if frost forms.

Image of a frozen suction line and compressor on a Carrier roof top unit.
Frozen suction line on a Carrier roof top unit

The most common cause of a coil freezing is low air flow. As the ice covers the coil, the air flow is restricted and accelerates the freezing process. Other common causes are refrigerant leaks, low ambient temperature, undersized liquid lines and dirty filters.

 

 

 

Image of a clip on anti-ice control
Clip on Anti Ice Control

Anti-ice controls are common on large air conditioning system and can be installed on any air conditioning system to shut off the compressor when ice is detected. This is a safety device to protect the equipment under extreme conditions when something has gone wrong.  There are contractors that will use the anti-ice control to mask a problem with an installation and can go undetected for years. When the coil is freezing the unit will use a lot more energy, drip water outside of the drain pan and shorten the life of the equipment. If the AC coil is freezing up, there is a problem that needs to be corrected.

One thought on “Evaporator Freezing”

  1. mackenzieAugust 24, 2012Great post. I just bouhgt a house and the air conditioner is broken. I wasn’t sure if I wanted to replace it or repair it but I think I am just going to repair it. I have been looking for a contractor. I just don’t know what kinds of questions to ask. I never had to do anything like this before. Thanks for the great information.

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