I remember a rash of nuisance service calls rolling in on weekends like this, the snowfall being the key part.  It is amazing how well prepared a Heat Pump is for cold weather, with safeties, defrost controls, and supplemental heat (in most).  Unfortunately, they do not come with windshield wipers to keep the condensers clear of snow, and snow will decrease the airflow across the condenser to a breaking point.

carneyphc.com

     For conventionally ducted heat pumps, a situation like this means either the supplemental heat turns on more frequent, or the homeowner must turn on the Emergency Heat to satisfy the thermostat.  When covered with snow, a conventional heat pump will not be able to move air across the coil and will actually start to recycle the air increasing the defrost cycle times and frequency.  I see this often on top discharge condensing units that may have been off during the snowfall, allowing the top to be covered.  If not serviced, this can start creating quite the ice sculpture.

     For the ductless mini-split heat pumps, this could create an uncomfortable home.  This is because these systems do not incorporate any sort of supplemental heat into their equipment.  During defrost cycles, becoming more frequent during times of snow and airflow restriction, the indoor coil fan actually shuts down to avoid blowing cold air into the home.  More defrost cycles tend to impede the operation enough that it could not meet the heat loss of the house.  Luckily for most of these homes, this is not the only source of heat.  This would be the time to fire the boiler or furnace.  Most of these systems will operate in defrost until a sensor in the condensing unit reaches at least 40F, taking much longer if snow is a restriction. 

     In order to avoid nuisance service calls, be sure to educate your customers on what to do during historic snowfall.  If not, you could experience more than just a nuisance.  Have you ever had to charge a condensing unit during a blizzard?  You guessed it, I have!  I looked a little ridiculous out there with my legs wrapped around a tank of R-22.  I should have told the poor old woman to not clear the snow away from her condenser with a shovel - she did not realize there was copper pipes behind it!   If concerned, you may want to recommend to turn on the back-up heat, turning off the heat pump, until after the storm.  This way they can clear the snow away from the condenser without issue.  I hope that I learned the hard way so you don't have to!

http://excessair.blogspot.com/2013/02/heat-pumps-and-record-snowfal...

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Comment by Christopher Morin on February 28, 2013 at 3:20pm

Good Evening Tom, I am sorry you appear to be so offended by my lack of response to an otherwise perfect post on your part.  Since you were not incorrect in your statement about properly charging the system in Cooling, under a load, I did not find a question in your previous comment.

Disappointing that no one in your area seems to be clearing away the snow to operate the heat pump - so you are saying they run the electric heat strips, or other fuel sources for what may be a month until the snow melts?  I wouldn't do this for all kinds of energy use and cost reasons, maybe you could be the hero and offer some customer education?  This would go the same for duel-source heat pumps too, not just electric supplemental.

Since operating the heat-pump in heating mode during the winter makes the line set the discharge and liquid lines, you would not be able to charge the system at the indoor coil.  Particularly on a mini-split, where there are no service ports at the indoor coil.  So, you would need to operate the system in cooling, weigh in what you can (after recovering the refrigerant, finding/fixing the leak, and pulling a proper vacuum), and return when the weather is warmer to adjust the subcooling.  This is if you are lucky enough to have a service port at the evaporator - most manufacturers are not so kind!  Oh, and it doesn't need to be 85F, 60F+ Condenser Entering Ambient is all that is needed from all manufacturers to adjust the charge with a TXV, 65F+ Return Air Dry Bulb.

So, next time please send me a message if you have some particular issue or question, instead of publicly questioning the validity of what others value as a great informational resource!  I hope you continue to read my blog, as I do like the opportunity for conversation and education.  Please be clear in future posts if you have a question!

Comment by Jose Macho on February 14, 2013 at 9:46am

I have a Fujitsu mini split DHP and live in CT-  I simply set the remote to 68 in economy heat mode and forget about it for the heating season.......The outside unit is elevated and is located in an area of snow drifts. We had 2+ feet of blizzard snow and I had no issues of any kind.. When I finally shoved out a path days later to inspect  there was no snow accumulation around the fan intake in spite of the mixed sleet/freezing rain  which than later changed to a more flufffy snow. I was more concerned with the snow and added rain load on my roof..

Comment by Christopher Morin on February 12, 2013 at 6:26pm
I don't think my blog was suggesting condenser unit replacement, but yes - until the unit can be cleared of snow the supplemental or emergency heat strips should be used to maintain comfort and avoid potential break-downs!
Comment by Bob Blanchette on February 12, 2013 at 4:14pm

Why couldn't the customer just use electric heat strips unit the weather was decent enough to replace the condenser?

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