Testing Mini-splits in winter temps.

[Ken Amelin]

For years we've (meaning me) stated that we can't test AC units when the temperature is lower than 60 degrees. Does that still apply or can we now test at any temp. How about mini-split heat pumps. Can we test in AC mode when outside temps are low?

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[Jim Luttrall]

For years we've (meaning me) stated that we can't test AC units when the temperature is lower than 60 degrees. Does that still apply or can we now test at any temp. How about mini-split heat pumps. Can we test in AC mode when outside temps are low?

You can typically run scroll compressors without fear of damage due to liquid slugging. Heat pumps also are almost certainly exempt for obvious reasons. But getting any meaningful results when ambient temperatures are that low is something totally different. The reason for NOT running a/c units below 60 is the migration of liquid refrigerant to the compressor and/or return line during cold temps. Liquids do not compress very well and will destroy the pistons and valves in the compressor. Modern scroll compressors do not have pistons and thus avoid the problems but there are still bunches of compressors with pistons still in operation. If you can't readily identify the difference then don't start the unit. The damage happens in the first few seconds upon start up. Some older units also have crankcase heaters that overcomes the problem but again, it is hard to tell if there is one present. If in doubt, DON'T.

[Gunnar Alquist]

Ken,

I posted a reply shortly after your original post, but apparently it was while Brian was upgrading and it looks like it got lost.

I used to make the same statement as you, but a local heating contractor let me know that it is ok to run an air conditioner in the winter. That said, we have a very mild climate here and it rarely gets to freezing temperatures for more than a couple of hours. You have much colder winters than we do and I would be reluctant to run an A/C without contacting the manufacturer first. If you get something in writing from the manufacturer that states that damage will not occur to a compressor during winter in your climate, then you have some ammo to defend yourself when the owner files a claim against you for damaging the compressor.

I agree with Jim, if you don't know enough about that particular air conditioner, don't run it.