Have a 2-year old mini-split system which is having some problems. Having a technician come out to address, but I like to make sure I'm informed enough to talk to them.

The system works fine for a while (heat), but after a while starts blowing cold air. Shutting off all the units, then restarting each One of the indoor units seems to be icing up, as there was an icicle hanging from it. The outdoor unit looks normal, it's not covered by snow/ice or anything unexpected.

I know with AC, freezing coils often indicates low refrigerant. But I've never considered a heat pump freezing up in the winter.

FYI, it's not all that cold here. 32 degrees, and the units are Mitsubishi "Hyper Heat", so outdoor temp shouldn't be an issue.

 

That sounds like the system is going into defrost mode. In defrost the system goes back into A/C mode. It tries to withdraw room heat and deliver it outside to unthaw the condenser. If there is no electric reheat.... you may feel cold air.

It's not only the outside air temperature.... it's also the humidity level. The higher the humidity the faster the unit will frost/ice up requiring more defrost cycles.

You could very well be low on refrigerant.

 

Interesting concept with the defrost mode. I'd imagine it's not supposed to go through that cycle too often.

I'll post back with more details - but I appreciate knowing more now than I did when I started!

 

I was looking further into Mitsubishi units with VFR (variable fluid) and it appears their system work more efficiently to defrost unit. From what I was reading there isn't supposed to be cold air flowing inside. I'm guessing to a certain extent that makes sense.

Interesting reading

 

The Mitsubishi "Hyper Heat" and cool are actually some of the better Mini-splits out there. As long as it was installed properly it will be fine not like the One I have in a rented apartment the install crew were lousy people both people and work ethic skills.

They will have to fix it now as I *fixed* it so it will not work in either heat or cool mode.

But I have seen a few of them completely covered in ice and frozen solid.

They are all them same model but not all have the Hyper Heat H2i badge Why don't know maybe older ones.

The place still has the 240V electric baseboards and I use that I would only use this for heat as a backup not the primary heat source.

 

Thanks Pete and CB. Had a tech out today and he troubleshot it to the reversing valve. Apparently there's a known issue with certain Mitsubishi models with the valve getting stuck in defrost mode (or something highly technical like that). The part is covered under manufacturer warranty, but I'm foreseeing a fight with who's going to pay for the labor. We'll see - it's a big local company who I definitely paid 'extra' for their support, so we'll see how it goes. They haven't said one way or another yet, so maybe I'll be pleasantly surprised.

But thanks Pete, you got me reading about the defrost cycles so when they said it was the reversing valve, I knew exactly what he was talking about!

CB - I do like the Mitsubishi units. I'm also a fan of the Fujitsu mini splits. Have 2 systems of each installed in rental properties. This is the first real issue I've had. Well, other than a poor install which caused a refrigerant leak. Can't really blame that on the units though - just the fly-by-night contractor I had install it.

Anyway - will keep you updated... really appreciate the help!

 

Not keeping the insides of the refrigerant lines clean during installation can allow crap into the reversing valve too.

 

Yep fly by night I hate them the company was out of NY and is no longer in business anymore!

Yes Mitsubishi & Fujitsu are the only decent units made.