Replies

1. 
   greenright | Nov 08, 2024 07:30am | #1

   Useful when running multiple mhk2 wall thermostats. The return temp
   Is averaged across all thermostats. For example if you have two thermostats and one reads 68 and the other reads 72 the system acts upon 70. So if your set temp is 70 the unit will consider the thermostats satisfied.

   You want this option to be 3 so temp sensing is at thermostat.

1. 
   mpd | Nov 08, 2024 11:35am | #2

   Thanks but I'm confused by your reply. Average Data from All Unit is Function Code 2 option 1, but you seem to be saying I want option 3 instead with multiple MHK2 units?

2. 
   greenright | Nov 08, 2024 04:41pm | #3

   You don’t want the unit to act on average temp between thermostats. This is for larger installations with larger number of thermostats where you want to maintain an average “close enough to set temp” indoor temp in the whole building. Instead I am sure you want the room where each thermostat is to be at the set temp and you want thermostat temp sensing at each thermostat … and that is setting “3”.

1. 
   mpd | Nov 08, 2024 08:14pm | #4

   Thanks. I have another (possibly dumb) question. My MHK2 is connected to an SVZ-KP36NA in my garage. Which unit does what - is the MHK2 like a traditional thermostat and turns on the heat pump when the room is not at the set point and turns it off when the set point is reached? Or does it merely send the set point to the air handler (or heat pump) and it is the air handler which senses (based on return air) when to turn on/off the heat pump?

   Or is it the value of the function code that determines which unit is doing the actual sensing and control of the heat pump (.i.e if 1 then sensing and control resides with the air handler, if 3 sensing and control resides with the MHK2)?

1. 
   greenright | Nov 09, 2024 08:36am | #5

   The value of the sensing code determines where temp is sensed.

   … and I assume you want the temp to be sensed at thermostat (always more accurate) rather than at the return air intake … and that is option”3”…

3. 
   user-5946022 | Nov 10, 2024 12:49am | #6

   These are great questions, and greenright, thanks so much for answering.

   mpd is running into what so many of us do - Mitsubishi Equipment is great, but their Diamond program is useless, and most of the people at the Diamond installers know FAR less about these units than an informed homeowner. For some reason, Mitsu does not want homeowners to understand their systems. Unless Mitsu either radically changes the Diamond program so that these folks actually know something about the units, or changes their attitude toward consumers, they will not do as well as they could. Very frustrating....

4. 
   mpd | Nov 10, 2024 12:04pm | #7

   My problem is that I'm trying to find out what is controlling the temperature. I have a multisplit system with an air handler in the garage for downstairs and 3 ceiling cassettes in bedrooms upstairs. The ceiling cassettes can control the temperature within 1/2 a degree - on my independent room temp sensors the overnight temp graph looks practically like a straight line at the target room temp. Downstairs overnight the MHK2/air handler system exhibits wild spikes, not smooth modulation at all - the swings are +/-2 or sometimes even +/-3 degrees and make no sense. I'm trying to fix this somehow but without detailed info about who's doing what (is it the MHK2 or the air handler) I can't tell why it's swinging so much.
   I found a blog by a guy who hacked his Mitsubishi heat pump which led to a github site with code to build a better controller that interfaces to the CN105 connector (which seems to be just a serial port) and another site which was documenting the control protocol so maybe I can find my answers there 'cause I sure can't get them from Mitsubishi or my dealer.

5. Expert Member
   Akos | Nov 10, 2024 12:13pm | #8

   On the hard wired Mitsu controller I set up, the options were
   -use intake air temp
   -use average of intake air temp and thermostat temp
   -use thermostat temp.

   You generally want to set it to use thermostat temp. Don't over think it. Set it to 3, see how it runs.