Mitsubishi Thermostat Question

[SnowB0und]

I have a MSZ-18NA mini split and keep having problems with heat mode "short cycling" when it hits the set temperature. Apparently this is a problem with these units as the thermometer inside the unit gets heated from the heat exchanger more than the incoming air, so it thinks it overshot the set temperature and shuts off, then realizes its cold and fires back up. The solution for this is to use a MHK1 thermostat.

I bought a MHK1 thinking it would work with my unit. It says it works with M series. But mine doesn't have a connector on the board. Its got the solder pads and it even says CN105 on the board (red box).

So heres the question, do I try soldering the wires of the MHK1 to the pads and see if it works?

My other issue with the unit now is there is no way to set a weekly program. I always thought I'd be able to add that on later and now I can't. Any other way to get a weekly program like any normal HVAC unit has on one of these?

 

[aardquark]

Not all M-series are supported. Here is a compatibility chart:
http://www.mitsubishipro.com/media/448697/compatibilitychart.pdf

 

[SnowB0und]

Yah I didn't know that before installing it. The remote said M series so I assumed it was all modern ones.

I'm trying to decide if I should solder it to the board and cross my fingers.

Anyone know of a IR remote that controls these similar to a weekly programmable thermostat?

 

[monkeyspanners]

Can you remote mount the sensor? Have done that in certain situations.

 

[Slednut]

This may help.

http://cleanenergywonk.com/2013/04/...-thermostat-to-mitsubishi-mr-slim-heat-pumps/

 

[Jackfre]

How big a space is the unit heating and what is the low/high output of the unit. Perhaps the spec on this particular unit has a rather high minimum heat number which exceeds the actual heat loss of the space.

This frequently happens with modulating equipment. Because everyone has been used to single stage equipment here in the US for so long folks don't realize that the low speed performance, from a comfort perspective is more important than the high output.

 

[SnowB0und]

Approx 900 sqft uninsulated 1940's house and its a 18,000 btu unit.

 

[SnowB0und]

Can you remote mount the sensor? Have done that in certain situations.

I insulated the sensor with a spray foam straw and heat shrink, seems to have helped quite a bit.

I don't have a connector where the CN105 goes for the MHK1 (which I bought thinking I had it). I want to solder the wires where my board says CN 105 should go and cross my fingers. That's an expensive gamble though.

 

[truckman5000]

I wouldnt worry about the thermostat being the answer on the short cycling.

Id have to say its alittle low on refrigerant.

I have 3- 15,ooo in my house that never "short cycle" and there sized for heating my home and are in rooms that are 400-600sq ft. Im a HVAC tech...