AC Unit Frozen Coil

AC working overtime…

One of the more frequent service calls for HVAC technicians this hot time of year is an AC unit frozen coil above the furnace.

Once the coil is frozen, the air flow through the system becomes blocked, and the house will not cool down. The condensate drain system can overflow and leaks around the furnace can develop that can cause other expensive repairs.

What’s the most common cause of a frozen AC coil?

A Dirty Furnace filter.  A furnace filter that is dirty will slow down air flow through the furnace and through the AC coil.  The slower air flow doesn’t transfer the cold air from the coil into the home, causing the coil to get colder and eventually to begin to freeze up. And if the furnace filter is very dirty, it can begin to collapse, allowing air flow to bypass the filter and build up on the bottom of the AC coil.  The coil effectively becomes the new filter.  This further slows air flow through the coil, causing more chance of freeze and ice build up.  While the picture shown above is extreme, any build up of ice on the coil will prevent the AC unit from properly cooling the home.  

Sometimes the simplest things can cause the biggest problems. Most people forget to replace their filter through the summer months. Change your filter monthly, to prevent costly service calls and to keep your system running smoothly.  And if your AC is not cooling well, consider a service call from an HVAC technician to clean the coil and evaluate the system performance.

Visit our Ask-Your-Inspector page for more home maintenance tips. Read more about our Inspection Services.