MHI split freezing up, hardly even cold here

[Sparkletron]

Hi fellas,
I've got an MHI 9kw high wall splitty, seems to be getting into the habit of freezing the condensor every hour or so, then taking half an hour to run through the defrost cycle.
I don't remember this happening last year, unit is about 2 years old.
I installed it. It's in a lounge / rumpus that is probably around the 75 square meter mark. The outside temp is currently 1 degree centigrade.
It's frozen up twice tonight.
What's your thoughts?

[Magoo]

low on refrigerant, a leak somewhere. But at 1.0'C ambient outside is nuisance temp as outside coil will frost easily, but should clear real quick if fully charged.

[Sparkletron]

Thanks for your reply.
I'll reclaim what's there and weigh it and see what it looks like.
Strange, I've got another little MHI I installed about 3 months ago for a bloke doing almost the same thing.
I went there today and checked it out, definitely still working, just freezing up at the drop of a hat.
I have pumped it down and left it with a 3000kpa nitro charge overnight, we'll see if she's dropped it tomorrow when I go back.
I'll drag the reclaimer round there and see what the charge is like in that one too I guess.

Cheers!

[Tayters]

Seem to recall reading something here about the air temp around 0-4*C then more chance of freezing up the coil as Magoo says but when it gets colder and into the minus figures then coil wont freeze up as much.
Thought Rob White posted it but couldn't find it so someone else but it was a regular poster.

Thanks,
Andy.

[Magoo]

Will be interesting to see what refrigerant weight you recover from system versus the nameplate system charge. MHI systems are fairly bullet proof performance wise, but that ambient temp can be a pain in the armpit, its the ambient RH % that kills the out door coil and frosting up. generally coils are super sized for that event and cyclic defrost should be fairly quik and not too regular. So thats why i suggested system leak, drop the suction in heating mode a few degrees and you will get massive out door coil frosting/ snow ups and slow defrosts .
Sydney has been friggen cold lately as well.

[Sparkletron]

Hi boys.
I went back and checked the smaller of the 2 units after I charged it with nitro.
It held the pressure, spot on. I bubbled up the flares and moved em a bit too. No leaks...

Anyway, the bloke who owns the little 3.5kw was really getting pissed with the situation. So I replaced it with a 5kw unit. I have the old u it, I'm yet to reclaim it, but I doubt it was low on juice
Within 3 hours of me leaving, it had frozen up and had gone into defrost for over half and hour.
It came back on and only ran for 40 minutes and did the same again.

Seriously, is this what can be expected from MHI?
In waiting for the 40 phone calls from everyone who I've put air cons in for in the hotter months now trying to use them for heating, only to discover they don't work ��

[Sparkletron]

1418114181Pic of the outdoor unit

[Andyfal52]

Sounds to me like due to the low ambient temperatures as your people are trying to us the AC in Heat Mode, the condensors are freezing up as it can't remove the cold from the room.
AC is not a specific Heater and when the ambient temperature is so low the condensor coil will constantly be freezing up and defrost cycles more regular.
Tell them to set the temperature lower (20 - 23) and this will achieve a longer period of heating. if they are setting temp to anything above 25 when u have a ambient temp of 1 they are basically in fantasy land if they think it's gonna work. Suppose it's what you told your customer when you installed it?

[al]

Just a thought from a country renowned for its damp and cold winters, did you check the duty at -5 ambient when you sized them? most units lose performance below zero, looking at this manual there is nearly a kw of duty lost at zero, 1.5kw lost at -5, if house insulation is poor then long run times and more frosting unfortunately

[al]

Manual, not sure if this is your unit though, page 14,

http://www.manualslib.com/manual/823679/Mitsubishi-Heavy-Industries-Srk20zix-S.html?page=14#manual

[nike123]

Since that unit (as many other manufacture) has outdoor coil TD ( at heating) of about 5-7K, heavy frosting is normal at ambient temperature between 0°C and 7°C with high outdoor RH.
Conditions will improve when RH got lower when ambient temperature go below 0°C or outdoor temperature go above 7°C regardless of humidity.
Check outdoor unit position that air is not recirculating.
In future, avoid installing air source heat pumps, in areas with high moisture in winter, as the only heating solution!