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Mitsubishi Hyper Heat minisplit thermostat questions


I've just had installed a three-head mini split from Mitsu. One thing I've noticed is that having the thermostats on the units themselves is... idiotic. So I'm considering installing (or having installed) the MHK1 wireless thermostats for at least one, and maybe all, of the indoor units.

Question to either installers or fellow owners who have had this thermostat installed: will the thermostat stop the indoor unit it's paired with from constantly running the fan on low to "sample" the air? I know the thermostat will be remote, but besides getting a better temp read, one huge potential benefit (for me) would be for the incessant (and annoying) noise to stop. For some reason, when the units are in sampling mode, the sound of the fans make a very annoying sound that is just barely audible. When I'm trying to work, it just drives me crazy, so if the remote thermostat will resolves this (after all, why would it need to sample if the thermostat is now remote), that would go a long way towards convincing me to shell out the money...

Please let me know if you need further details (like specific model numbers, which I'll need to dig up).

I'd also be *very* interested in anyone that has had the 'PAC-US444CN-1' installed on their indoor units. Apparently this item will allow you to use your own thermostat with the indoor unit, meaning I could start using my ecobee again, which I would love. I'm interested in hearing from someone who has paired their ecobee/nest with the mitsu indoor units: happy/sad? Anything you wish you had known before doing it?

Thanks so much!!


  • mgdesrochers
    mgdesrochers Member Posts: 20
    The MHK-1 will stop the indoor units from sampling, it can be set to sense temp at the unit or at the control (at the control is default) & it is part of the installer set-up programming.

    Unfortunately I don't have anyone with the PAC-US444CN-1 so I can't speak to user experience on that part of your question but there are a lot of professionals here besides me so hopefully someone else can tackle that part for you.
  • GW
    GW Member Posts: 4,302
    I was told the thermostat interface is fussy, yet I've never installed one. If the fan is annoying you just get the mhk1 and get the Honeywell modem thing to connect to your phone app.

    I thought you needed to clip a jumper to kill the constant fan, theres a setting for that?
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]
  • csumner2020
    csumner2020 Member Posts: 1
    I have the PAC-US444CN-1 installed on my home unit and did the install myself. These interface modules allow for the use of a single stage, single speed fan OR a thermostat with 2-stage heat cool AND/OR multi-speed fan (3-speed). Here is the problem with utilizing a Nest or Ecobee thermostat... The newest Nest stat gives the option to choose 1 of the 2 options, you cant have both. After choosing to use the the 2-stage heat/cool option on the Nest you are left with only 1 call for fan. The module then has to be set to this variation by flipping some dip switches inside the interface. The module then communicates with the indoor units internal temperature sensor and utilizes this along with run time to handle the call for fan staging. The other option would be to utilize the the 3-speed fan option from the Nest in this instance the nest basically calls for speed 2 of the fan based on the call for 2nd stage cooling. Same in this case, dip switches are set inside the module to let it know you are only calling for 1-stage of heating and cooling then the interface makes the determination of when to call for the 2nd stages.

    I have really played with these variations alot. In a perfect world you would use the interface with a thermostat that has 2-stage heat/cool AND 3-speeds for the fan, which I have also tried. The bad thing about using this kind of stat I havent found 1 yet that plays nice with the standard home automation communication protocols, Z-wave, Zigbee, etc..

    I will also add that today Ecobee released the Ecobee4 stat with Alexa built in. I have already looked at the limited information available for the thermostat and don't see where they have added the support of multispeed fans. This of course doenst mean it can't be used with the module it just mean that the module will have to handle the staging of the fans which it can.
  • hvacfreak2
    hvacfreak2 Member Posts: 500
    The MHK-1 , I accidently got mad and smashed one about a year ago , now it works fine. The factory remote is the only thing I would use. Use a PAC-SE41TSE remote temp sensor and control with the factory remote is the best option.

    Mechanical Enthusiast

    Burnham MST 396 , 60 oz gauge , Tigerloop , Firomatic Check Valve , Mcdonnell Miller 67 lwco , Danfoss RA2k TRV's

    Easyio FG20 Controller

  • tim smith
    tim smith Member Posts: 2,397
    the pac us I feel was a arm stretch attempt at getting unit to be Internet connected to today's control in favor for domestic use. A bit half baked. They have changed a bit since inception but could do better. I would stick with Mhk if I were you. If I remember right, you can get a Honeywell redlink gateway and connect with phone app also.
  • NickKensington
    NickKensington Member Posts: 1
    I just purchased ( April 1, 20-18) a ducted Mitsu system (2 1/2 Ton) outdoor hyperheat (PUZ HA30 NHA5) and indoor air handler PVA30AA7; It has a 10 KW back up electric heater in it.
    It came with a MHK-1 wireless thermostat. This thermostat does not indicate when the 10 KW electric back up is on or not; The temperature setting in the thermostat will not go above 83 or below 50 in heat mode; The fan will stay running even when the set temperature is achieved . ...and runs constantly. Since this system supposedly makes use of the electric back unnecessary, it is very frustrating that so far I am forced to use the electric back up heat....I am complaining about this thermostat to far not pleased with it...,NickKensington, Boston
  • the_donut
    the_donut Member Posts: 374
    edited April 2018
    Not a fan of the factory remotes unless install is for single family. Unit has cooling preference and will not enter heat mode if one of the zones calls for heat, at least the generation we have. Also Mitsubishi uses a snowflake symbol for heat and sun for cooling symbol, which bugs the crap out of me and is confusing for first time users. Had a 26 unit apartment complex with 3 apartments same unit. 1 person using a.c. mode at 20* gave us no heat calls (secondary source of heat to a baseline boiler load). Apartment was 60* without minisplit to regulate temperature (and tenant wanted 80).

    Had another incident where tenant thought sun symbol was heat. Spent half of winter without until we came by on a routine inspection. Tenant had no idea unit wasn’t functioning in right mode, even though apartment was 60*. She just chalked it up to old building, drafty room.

    Also remotes are dodgy without fresh batteries and sometimes don’t synchronize with mr slim.
  • mrblister
    mrblister Member Posts: 4
    Following up here on the PAC-US444CN-1 interface, I've installed two of them in our home along with 2x Nest thermostats (yes, aware of the drawbacks with a VRF system), and am running into the following issue (paging csumner2020):

    Even in stage 2, the compressor is not working anywhere near max, and the heating and cooling rates of change are significantly lower than when a 'standard' Mitsubishi thermostat is connected. According to the guides, Stage 2 should 'ramp the indoor unit to full capacity' whereas Stage 1 will 'optimize variable capacity', but I'm not seeing this in practice, and it can take hours to cool down a few degrees. Fan speed seems to work fine, and I've played around with the dipswitches on the device to make sure static pressure, etc are correct.

    For reference, I've got an MXZ5C42NA exterior unit and SEZKD18NA4R1 + PEADA24AA7 indoor ducted units.

    Really appreciate any help!
  • wpmike
    wpmike Member Posts: 13
    I thought I would mentioned that I used a wifi enabled Kumo Cloud device combined with a remote temperature sensor. I can control the mini-split with my phone anywhere. The temperature sensor built into the head is not very good. Here are the link for the two devices you will need from mitsu.
  • ratio
    ratio Member Posts: 2,919
    Have you verified that it actually is calling for second stage cooling? Check with a meter at the adapter, or try using jumper wires to force it to high cool.

    Is it apparent at the condenser when the unit goes to stage 2? If that unit has a VFD on the compressor, you might try monitoring the output frequency to see if the system is trying to ramp up.

    It might take a call to tech support to find out what's going on.

  • mrblister
    mrblister Member Posts: 4
    @Ratio - Thanks! I'll try checking it at the condenser to see if it's actually calling for 2nd stage.
  • mrblister
    mrblister Member Posts: 4
    OK, so I've done quite a bit of experimentation and I'm still stuck:

    tl;dr: Heating works well, but cooling works sub-par, regardless of the thermostat connected. Can't figure out why.

    I connected Mitsubishi thermostats to both air handlers, in order to figure out if the thermostat interface was at fault. Also increased the amount of coolant in the system. Results are now as follows:

    Ambient Temperature Outside (~70)
    Heating: Intake 70, Output 96
    Cooling: Intake 68, Output 58

    Any idea what to do next to figure out what's going on?

  • kevink1955
    kevink1955 Member Posts: 75
    How did you determine how much "coolant" to add, sounds like will need the help of a pro real soon
  • mrblister
    mrblister Member Posts: 4
    edited September 2018
    @kevink1955 this was all done by my installer, presumably correctly. They just haven't been able to figure this thermostat/cooling issue out which is why I've been doing the legwork myself. Please excuse the novice aspect of things, I didn't know a single thing about air conditioners or heat pumps until a couple months ago.
  • kevink1955
    kevink1955 Member Posts: 75
    Glad you have a Pro handling things but even adding refrigerant has a procedure that needs to be followed. You just do not add some, the system needs to be recovered and the refrigerant weighed and recharged to the manufacturers specified weight. Looking for trouble any other way.
  • SuperJ
    SuperJ Member Posts: 605
    With the MHK1 You set the fan to stop during thermal off for heat and cool (separate settings). (settings 125,127).
    Setting 173 lets you specify whether it uses the internal or remote sensor for temperature sensing.

    See the install guide: