Mr Slim MSZ/MXZ model don't shut down completely

[kingofbytes]

Hello,
recently I purchased a large installation of a Mr. Slim system that has a combination of the wall mounted units and the horizontal ducted units.

I've also learned that evidently these systems don't shutdown the fan when temp is reached - it just runs at an (alleged) low speed mode.

For the horizontal ducted units, however, this is an unmitigated disaster, especially in bedrooms. Blowing "room temp" air and creating air currents in a bedroom during a heating cycle because temp has been reached is, in practice, awful. Blowing room temp air (or slightly cooler) while sleeping feels very cold on the body.

Saving money on electricity is NOT my issue - I've seen that posed in another post to "just let it do it's thing" - that it not a solution for the problem of air currents created by the ducted system.

Is there a way to revert the system back to a "standard" method of shutting off the fan when temp is reached? If not, manually turning off the system and manually turning it back on to stop the drafts is not what I expected for a $40K system. Thanks to anyone who can help stop the drafts!

 

[hurstscrambler]

I have never tried to change that aspect of the units, where are you located? I would call the installer and get him to call his equipment source to see if there is a programming measure you can use to change it. Unfortunately, I don't think there is, but it's possible. It is a pretty big blunder on the manufacturers part if you can't change or modify it.

 

[kingofbytes]

I'm located near you in NH, hurstscrambler. This is a HUGE blunder imo. I thought I bought the Mercedes system and instead feel like I got the Hyundai.

I've been in touch with my installer and they're working with me, but it's been slow and sometimes frustrating. I don't blame them for the engineering of the unit(s), but they're the front-line representative [to me] regarding Mitsubishi. Had I known these things never shut off I'd definitely have chosen another option.

Frustrated in NH

 

[hurstscrambler]

There is a guy at API in Manchester who knows everything there is to know about those, I forget his name, maybe Mike.... If you post up the model # I can call, we buy a lot of equipment from them for commercial applications.

 

[kingofbytes]

Thanks hurstscrambler. I truly appreciate the assist. I'll give it a shot with the model numbers:

I've got 3 outdoor units, 2 are 36K the other is the 48K:
MXZ-4B36NA-1 (Qty 2)
MXZ-8B48NA (Qty 1)

Indoors, I've got 2 of the horizontal ducted units, 10 wall mounts anywhere from 6K to 12K. I believe those part numbers are:
MSZ-GE06NA
MSZ-GE09NA
MSZ-GE12NA
MFZ-KA12NA
SEZ-KD18NA4

Also, for completeness, I purchased the wireless kits for every unit including the "totalconnect" internet access cable modem.

 

[hurstscrambler]

Can you post a pic of which t-stats you have, I made a few phone calls and think I have an answer. If you have the controllers I think you have, they look like standard Honeywell stats, you can go into the Setup Functions menu and change parameters 125 and 127 both from 1 to 2.

 

[kingofbytes]

It's the MHK1 and YES I was looking through the manual and found those options. Here's the pic:

I'll be trying those out later today!!!!!

 

[hurstscrambler]

Cool, let us know !

 

[hurstscrambler]

Fyi, I assume one of those parameters is for heating and one for cooling. I d think that if you were looking for cooling the fan wouldn't be a bad thing. The units were designed to have them running. I would consider just changing the fan operation for the heating cycle only.

 

[kingofbytes]

Thanks, that is indeed exactly what I planned to do. Nice to have a cool breeze in the summer - but not the winter.

Here's the preliminary results:
On the attic mount units, the change has stopped the fan from running - I'll be happier after 3 days of success, but this looks promising.

On the wall mount units, options 101-128 are NOT available to be configured - therefore you cannot disable that fan functionality on those particular units. That's a bit maddening but we're making progress. I'll do a more complete write up in a few days.

Thanks for all of your help hurstscrambler!

 

[hurstscrambler]

It makes sense that you can't change the wall unit, I understand it not being ideal for you, but it makes sense. With the actual ductless units, having the constant circulation is the only way to keep the space at a consistent temp.

 

[sneezer41]

With the wall unit, change the louver settings so it does not blow on you. If the unit reaches temp very quickly and bothers you[happens to me in cooling mode] turn the fan speed to very low. You probably have more output than you need, and the unit makes assumptions about what is going on based on in being more closely matched to the space.

These are great units but there is a bit of a learning curve and they are slightly less set it and forget it than regular heating systems.

Staying on helps with efficiency and air flow.

 

[kingofbytes]

I've change all the settings on the wall units to "oscillate". That results in more consistent room temperature than the default (which points it down to warm up the coolest air). That may be counter-intuitive, but the results are what they are.

As for "always on", I fully understand the arguments for "efficiency and air flow" and respect them. However, the notion that I cannot disable them in my own home is maddening.

As for the attic mount units, I can say I'm happier since I've disabled the parameters 124 & 125. It will actually stop the fan from continuous blowing which is proper.

However, I'm working with my HVAC contractor who is working with Mitsubishi support to figure out why I'm overheating the set zone temperature by +3 & +4 degrees. For example, if set to 68 degrees, the unit is heating to 71 and 72 degrees consistently before stopping the heating cycle. It was this way before and after the changes to 124 & 125 (something we thought 124 would fix).

I'll keep posting as improvements occur and will also compile a "real world" setup guide that will show changes I've made to my system that are optimal.

 

[Jackfre]

I'll be interested to see how your comfort and economy work out for you. That is a great system. I ran into this "constant fan" issue many times and in my trainings always spoke of the need to first of all understand that they run only low enough to be able to sense room temperature and respond accordingly. That makes positioning of the equipment a key factor. Don't locate the evap over the couch or over the bed. It is unfortunate that this wasn't discussed. Please keep us posted. I think you made a great buy.

 

[hurstscrambler]

Is the temperature overshoot issue a because the unit maybe has a minimum run time? There may be a parameter in the stat to change the deadband and aid shoot cycling, and in turn make it so that the unit needs to run for it's minimum time to make temp. Andy

 

[purevil115]

I have a Mr. slim in my garage and I do hvac for a living. I have noticed the same thing with over shooting the thermostat, I only have cooling but it can be a bit odd. I set for 72 and it never shows what temp the room actually is and I brought in another stat to see how off it was. Not a big deal and the thing only uses 286 watts to cool a garage so Ill take a solid product that is bullet proof and just let it do its thing. Plus its basically silent.

 

[purevil115]

I haven't used the Honeywell stat with the mini split but I know the remote has no way to change anything, the Japanese don't believe in you messing with there engineering.

 

[hurstscrambler]

Is it just the wall units that overshoot, or all of them? With the wall unit it makes sense, cause the Tstat reading the space temp of the wall but the unit will run till it's internal sensor is satisfied. I've never seen one of the ducted air handlers, but I assume they use the Tstat like a conventional system.

 

[pseudorealityx]

If you're getting drafts on the ducted units, then the air distribution was designed poorly. The units in 'low' should not have enough airflow to cause drafts.

The only thing I can see doing that is if the air distribution is sized to the point that at low speed, the face velocity over the diffusers is so low, that they just dump instead of spreading the air. We ran into that on a recent project that had VERY tight temperature control requirements, and the previous engineer made the mistake of using too many supply diffusers and instead of introducing a lot of mixing, the velocities were too low, and they just dumped out without mixing.

 

[hurstscrambler]

So your thinking they oversized or put too many runs off air handlers? So when the fan slows down the duct static pressure is too low. I suppose it's possible, but it is a fine line, maybe you can get the contractor to come back with a balometer and manometer to really see what's happening and know if your with in the manufacturers designs . What style registers did they use? Pic? I don't see the issue with having the fans off on the ducted unit, is there?

 

[pseudorealityx]

So your thinking they oversized or put too many runs off air handlers? So when the fan slows down the duct static pressure is too low. I suppose it's possible, but it is a fine line, maybe you can get the contractor to come back with a balometer and manometer to really see what's happening and know if your with in the manufacturers designs . What style registers did they use? Pic? I don't see the issue with having the fans off on the ducted unit, is there?

Just saying it's a possibility. I would say the chances in a residential application are pretty darn small. Oversized ductwork is certainly not a typical a problem in residential construction.

But location of the vents and how they're directed could certainly cause the issue. By the time gets to the occupant, you want the velocity down pretty good, under 50 fpm or so.

As far as the fans being on or off.... keeping the fans on helps to prevent stratification, and the longer you pull air through the filter (the ducted horizontal units should have a 'normal' HVAC filter), the better. Being that this is a very high end application (based on quoted $40k price tag), there may be a source of ventilation air brought into the system, and in that case, you need the fans running to actually do that.

 

[kingofbytes]

Many thanks for all the responses. I'll see if I can answer them one by one since my last post.

1. purevil115: There are many installer options that can be changed with the Mitsubishi thermostat (OEM'd by Honeywell).
2. hurstscrambler: Minimum runtime is something to look into and I'll ask my HVAC person about. That said, ALL types of units (Floor, Attic, wall mount) are overshooting temps consistently. I set for 68 and they're always 70 or 71 degrees.
3. Pseudorealityx: They used whatever that tool is that measures size/velocity at both the return and supply and were within acceptable parameters. So I do not believe the ducts are misdesigned - but I'm no expert so I really don't know. Seems like what they did was smart though. They also worked with Mitsubishi on the design of the system since it wasn't small (10Tons for 6000SF). I will say Mitsubishi initially messed up the return sizing (by 50%) and the HVAC company caught it, notified Mitsubishi and revised everything.
4. Psedorealityx: The only source of ventilation air I'm aware of is from the returns. Also, they triple-checked every seam/joint on the runs - and there's so much insulation around everything.

As I've mentioned the change to shutting off 124 and 125 in the configuration of the attic units has been a godsend during the heating season. One major issue that remains is the temperature overshoots. One other issue I've noticed is that occasionally, a thermostat will show 66 degrees, be set to 68-heat, and no heat will be coming out.

The HVAC company explained that it could be the defrost cycle that these units will occasionally do - but I've checked every hour in some cases and the problem persists. One of my workarounds is to click up the temperature 1 or 2 degrees (from 68 - 70 for example) and within 5 minutes, the unit blows out good heat.

But for $40K, I don't want any gremlins

 

[sneezer41]

I have lived with these units for ac and heat for some time. Do what I suggest and report back

turn the fan speed on any unit that is overshooting heat [or undershooting cooling] to low. Don't consult the AC guy or argue the logic, just do it for a few days and see what happens

If the breeze bothers you turn the vanes so they do not blow on you

the side to side vanes can be used to either blow air in a direction that helps spread air flow to harder to reach areas, or just off of you, like in my bedroom, the unit is near the foot of the bed, so the vanes are pointed way off to the side so that they never blow on us.


I think they are oversized for the space they are in. They prefer to be undersized so they can run all the time. Turning the fan speed down makes them feel undersized. When the temps fall you will probably find your problems are not as serious, as the unit swill now have to work harder.

 

[purevil115]

Yeah I have been thinking about the honeywell stat. Its a redlink stat so you can control it from the honeywell app. Right now I have the honeywell wifi stat controlling my garage furnace and have an extra contactor that when I turn the cooling on the honeywell stat it closes a contactor and powers up the mr slim outdoor unit. I cant control temps but I just leave at 72 degrees and can turn on remotely this way. Luckily the mr slim has auto restart function that remembers it was set to 72 before the power was turned off. Idk if the 250 bucks for the honeywell stat and 100 for the internet gateway is really needed.

 

[kingofbytes]

Thanks sneezer, I'll give it shot and report back. Incidentally, in case anyone is interested, I did an "as-built" in visio for those that are visual (like me). Let me know what you think.

 

[sneezer41]

Waaay oversized unless you live in the white house.

Turn some units off completely, especially in this weather. The harder you make them work the happier you will be. A foyer unit for instance might only be needed in sub zero weather

 

[kingofbytes]

That's been tried when the weather only called for heat 'sometimes' during end of Sept/Oct - some rooms down to 62 degrees while other's 70 degrees with heat on. That's not what we want.

Also, the design seems accurate based on other vendor quote's specifications I had before the installation - all measured rooms and proper calculations done (presumably). I have lots of vaulted ceilings 12 - 15 feet in some cases. All vendors were within a ton of calculation (9-10Ton)

I'll post back more as the HVAC guys are here tomorrow to do more troubleshooting - I heard anecdotally that the factory may have incorrectly set some jumpers leaving the factory - that is, the manual will say default is '123xyz', but may have left the factory '234yza'.

We'll see.

 

[sneezer41]

YOur vendors are idjits

HOw many square feet?

how old a house?

I know they are twice as large as they need to be.

My master suite is 500 square feet, and the 9000btu mitsu mini split is wildly oversized, but they do not make a smaller one.

heat and ac in the laundry?

really?

 

[purevil115]

You guys keep saying these are oversized but arent the outdoor units inverter series. I use a 9000btu cooling for my 600sqft garage and its slightly oversized but ramps down so much it just runs almost none stop.

 

[purevil115]

ALthough they could be stupid oversized in which case even lowest setting is too much, thats just crazy.

 

[kingofbytes]

Seems this thread is going a bit sideways now. Not sure the stone throwing helps especially since the HVAC company involved Mitsubishi from the beginning and worked with them on design validation.

Also, Mitsubishi does make a 6K and they used to make a 4K - so I'll assume there's an apples to oranges comparison being made there.

Moving on, figuring out why there are 3 and 4 degree overshoots is the call of the day. Keeping it simple, in a good sized room around 600SF with a 9K set to 68, I'm still looking for why the thermostat wouldn't tell the unit to stop providing heat at, oh, say 69 degrees and still pumps out heat to 72 degrees before it decides to back down. Doesn't matter what room, what BTU's, whatsoever. That's just insane.

 

[sneezer41]

So let me ask you a question:

My heater doesn't work right, why?

...


...


...


How come you can't answer?

Because I did not give you enough information

Answer the damn questions

unless you are just whining, in which case, nevermind

 

[JakeKohl]

Seems this thread is going a bit sideways now. Not sure the stone throwing helps especially since the HVAC company involved Mitsubishi from the beginning and worked with them on design validation.

Also, Mitsubishi does make a 6K and they used to make a 4K - so I'll assume there's an apples to oranges comparison being made there.

Moving on, figuring out why there are 3 and 4 degree overshoots is the call of the day. Keeping it simple, in a good sized room around 600SF with a 9K set to 68, I'm still looking for why the thermostat wouldn't tell the unit to stop providing heat at, oh, say 69 degrees and still pumps out heat to 72 degrees before it decides to back down. Doesn't matter what room, what BTU's, whatsoever. That's just insane.

I have a couple of LG units and had temperature setpoint issues with them. I don't have the wall mounted thermostats but I looked into those when I had my problem. I learned that (at least for the LG brand) the wall mounted thermostat was only a wired remote control for the unit. It did not actually do any temperature sensing. All of the ambient temperature sensing is inside the wall unit and this is why it needs to have the fan on constantly in heat mode. Ideally, the units never stop heating or cooling but only modulate the run speed of the fans and compressor(s) to find a steady state on mode.

It's like cruise control in your car. If you were on the interstate trying to run about 70 mph, you don't let the car slow down to 65 and slam the throttle until you reach 75 and repeat - that would be silly and waste a lot of gas...but that's what the traditional heat pumps do. The inverter units maintain the energy output through modulation and conserve energy by being on at the right power level.

Working back to your question, my LG units also have an "AI" mode where they let the temperature drift a bit but will automatically cycle between heat and cool. I still haven't figured out the science behind it - the room seems either too hot or too cool...perhaps you have it in some sort of intelligent mode instead of a fixed setpoint?

 

[wbabbott]

I'm resurrecting this thread as I found it while trying to find out why my newly installed Mitsubishi Mr. Slim ceiling mount unit had a constantly running fan. This new unit was installed in a new room addition to my house where hooking in the existing HVAC was cost prohibited.
This room addition is my hobby room and is not used daily basis or even weekly basis. The Mitsubishi wireless thermostat that came with, and was installed with the unit works, but unlike a wireless thermostat I installed on an existing PTAC unit in my sunroom, the fan does not cut off once the heat or A/C reaches the set point temperature. The fan just stays on. Like Kingofbytes, I was trying my best to figure out why the fan wouldn't cut off !! This thread helped a lot and I will be changing the 125 and 127 parameter as suggested.
The other question I had on this wireless thermostat is the "Auto" fan mode? It's strange when I first set up the thermostat the Auto Fan mode was listed on the thermostat, but then "disappeared" and only the Low...High setting is visible where you select bars between Low and High as a manual setting. Am I missing something ???

 

[[email protected]]

In order to get the fan to turn off after temperature hits the set point, you need to change the advanced configuration setting #125 . Change from 1 to 2

Link to Manual with instructions to access advanced settings,

http://s3.manualzz.com/store/data/0...b&r=1&fn=27635274.pdf&t=1522890863087&p=86400

Need to press and hold “up arrow” and second button from left side of MRCH1 controller to access these advanced settings..