Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

HW T-stat RTH9585WF to Mitsubishi Heat pump Via PAC interface

I recently installed a new Honneywell T-stat to gain WiFi control at a vacation home and have been having issues with the AC ever since. The unit ran at first for a few hours then stopped, to get the cooling working again I can manually change to heat mode then back to cooling mode. Again the AC will work for a period of time then just stop. I can check the system status via the T-stat and it shows both cooling stages and the fan to be running, but this is not the case.

T-stat is wired; C,R,Y1,Y2,W1,W2,G.
T-stat is also configured for Heat pump, I did try forced hot air mode briefly but may revisit after reading a few other posts on the PAC interface.

I believe the issue is related to the T-stat/PAC setup as I have two units acting this way.

Any input would be much appreciated.


  • ratio
    ratio Member Posts: 3,180
    The PAC-US444 exposes a standard—not heat pump—thermostat interface. See http://mylinkdrive.com/USA/Controls/InputOutput_Modules/Thermostat_Interface_for_Module/PAC_US444CN_1?product for all the paperworks you could ever want on it.

    That said, I'd be checking the actual inputs on the PAC to see if it's loosing the calls, which would imply a thermostat issue vs an interface issue.

  • SMAC1
    SMAC1 Member Posts: 2
    Thanks for the link, Lots of good information. Heading up to the house this week to check things out. I also noticed a water stain on the front of the unit, seems like the condensation drain could be blocked. Going to check to see if the drip try has a overflow switch as well. Maybe this could be related.