How to Prevent an Ice-Frozen Heat Pump or Air Conditioner by Setting the Defrost Cycle Time

March 3, 2010 | by Kim (email) |

iced over heat pump compressor unit

Last year, I wrote about fixing the ice-frozen outside compressor unit for our heat pump.  This winter has been record-breaking for precipitation here in Maryland, however, so I found I needed to readdress the issue with our HVAC guy. What I learned?  I can adjust the frequency of the compressor’s defrost cycle on my own to keep up with whatever Nature sends us.

With all the freezing rain and snow we’ve experienced this fall and winter, our compressor’s defroster just wasn’t keeping up.  Turns out, it was set to run only every 90 minutes of running time.  An energy-efficient setting, but not frequent enough for this year’s weather.

Mike showed me where to adjust the settings inside the removeable side-panel on the outside unit.  Yours should look much the same.

We moved the white clip from the 90 minute setting to 50.  If that turns out not to be frequent enough, we will move it to 30 minutes, but so far we seem to be doing fine with 50.

heat pump ac compressor unit defrost cycle timer adjustment

So depending on where you’re living, how cold it is, how much precipitation you’re getting in the cold weather, and where your outside unit sits (ours is under our deck – never directly in the sunlight!) you can adjust your defroster settings accordingly.  For those living in the southern U.S., you should be fine with the 90 minute setting.  Our friends in Canada and the northern U.S. states may need it to run every 30 minutes in the winter.

Note that the settings are how often the defroster kicks on during system run-time. So if your compressor runs for 10 minutes, turns off for a half an hour, then runs again for 15 minutes, that’s 25 minutes of run-time, even though 55 minutes have elapsed.  Ours was going a few hours before it had run for the requisite 90 minutes to engage the defroster and that was too infrequent for our unit this winter.

Running the defroster does, of course, use extra energy, so you don’t want it to run more frequently than you need it. That’s why we dropped to every 50 minutes rather than jumping straight to a defrost cycle of every 30 minutes of run-time.  Should we have a really mild winter again in the future (as we have most years in the past), I may move the setting back to 90 minutes.  But for this year, it’s not worth the risk of damaging the unit (ice-chunks building up and causing damage to the spinning fan blades and subsequently to the motor) just to save a few cents in energy cost each week.

Hope this is helpful to someone else out there!  It’s a quick and free first-resort solution for dealing with an iced-over unit that otherwise is in good working condition (and can help trouble-shoot before you call an HVAC repair person and pay for a visit).

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