[NA] Heat pump frost

[Let'sgoflying!]

33°F 70%RH

I noticed the outdoor unit making an odd fan-noise this morning - the coils were solid frost and not permitting any air.
The house remained warm and I did not smell the heat strips.
I ran the A/C a few minutes; frost can right off, I let it go another 15 mins for the moisture to dissipate.

An hour later, more frost and time, in sections.

Ignore?
Prepare to replace?
Some preventive intervention?

 

[Larry in TN]

I copied your post into Microsoft's AI tool. Here's it's output.


It sounds like your heat pump might be experiencing a defrost cycle issue or restricted airflow. Here are a few things to consider:

1. Defrost Cycle: Heat pumps have a defrost cycle to prevent ice buildup on the outdoor coils. If the defrost cycle isn't working properly, ice can accumulate and cause the fan to make odd noises1. You might need to check the defrost control board, temperature sensor, or reversing valve.
2. Restricted Airflow: If there's restricted airflow due to a dirty air filter or debris around the outdoor unit, the coils can freeze up. Make sure the air filter is clean and there's no debris blocking the airflow1.
3. Low Refrigerant Levels: Low refrigerant levels can also cause the coils to freeze. This is something that should be checked by a licensed HVAC technician1.
4. Moisture Dissipation: Running the A/C to defrost the coils and letting it run for a while to dissipate moisture is a good step. However, if the issue persists, it might be a sign of a more significant problem.

Given the recurring frost and noises, it might be best to contact a professional HVAC technician to diagnose and fix the issue. They can ensure that your heat pump is functioning correctly and safely.

 

[AKiss20]

Any heat pump should have some form of defrost logic to run a defrost cycle which puts the outdoor unit in cooling mode but doesn’t run the OU fan (pumps heat from the house directly into the fins). Some are just every X minutes when the temperature is less than Y degrees and some are more advanced but it should have it. If you aren’t seeing defrost cycles at these temperatures every 60-90 minutes of run time, there is likely something wrong. I would reach out to your HVAC company.

That being said, that level of frost is normal to build up in between defrost cycles. So if it is running defrost cycles normally I wouldn’t be concerned. My heat pump gets frostier than that and still works fine (granted it is a cold weather heat pump that theoretically gives full output down to -5F) so if you’re getting actually zero heat at that level of frost (as in 0-2F rise across the indoor coil, not like 15F-30F which is a typical temp rise across a heat pump coil in the winter) then something else is likely wrong. Again reach out to your HVAC company.

 

[Capt. Geoffrey Thorpe]

They frost up regularly, and the defrost cycle sounds "odd".