The Motor Switch Terminal, Model MST, is a 24 Volt, AC two-position motor. This motor is used with Trol-A-Temp and EWC opposed blade dampers, automatic registers and diffusers. The MST replaces the similar Trol-A-Temp model and the EWC MAN model.
The MST requires a Single Pole-Double Throw (SPDT) to operate the motor to the open and closed position. Once the motor reaches the Open or Closed position, the motor's internal end switches cuts power to the motor. Therefore the MST only uses power while moving between open and closed. Once the motor is in either the open or closed position it consumes no power. The MST also has 3 auxiliary end switches that can be used to turn on the furnace, fan or cooling when the damper is open, as well as control a secondary slave damper. See the legend below for the function of each terminal.
Terminal Functions
1. 24 Volt Power Common -C 2. 24 Volt Power Hot -R 3. End Switch, makes to 2 when damper is 50% Open and breaks when 50% closed. Typically used to turn furnace on for Heating Only. 4. Makes with 5 to drive motor OPEN. 5. Common of switch and makes to either 4 or 6 to operate damper. 6. Makes with 5 to drive damper CLOSED. X End switch that makes with 2 when damper is closed. Typically used to control slave damper. Z End switch that makes with 2 when damper opens. Typically used to control a slave damper.
Comments aboutHoneywell Trol-A-Temp MST Motor Switch Terminal:
It was an exact replacement for the damper motor that died. Easy to duplicate the same wiring positions as the old motor, using the same number and letter descriptions.I bought and installed 2 and then realized the third one was bad, so I ordered another one immediately.The price was very good. I just wish I had ordered 3 the first time [...]
Comments aboutHoneywell Trol-A-Temp MST Motor Switch Terminal:
Someone said you lose one of these every few years but that is not my experience. In 25 years I had lost one circa year 5 and got an actual Trol-O-Temp replacement for it. Funny thing is that it was the same one this time in a three zone system. I'm wondering if there is something wrong with that zone. I almost changed out the whole control system a couple years ago when the oil fired furnace had to go, because parts were thought to be no longer available and I wanted to switch to a dual fueled situation. Anyway, this unit looked good out of the package, but something changed in that it had to be forced into the mounting box. So much so a piece of plastic broke off the box about 3/8" by 1.5". I covered the gap with duct tape and kept going. The instructions were the same that I kept from start-up installation 25 years ago, cool. They say start up is "closed", but for me the thing went "open". It's in the worst of my three locations, but I took it back down and reset the cam so it would work for me and put it back. Now it wouldn't work at all (kept spinning), but son who is less than 25 years, found a problem with my eyesight and wire coloring. He switched the two offenders and . . . wallah! I'm good for another 25 years. Or maybe the next guy is.
Comments aboutHoneywell Trol-A-Temp MST Motor Switch Terminal:
The MST replacements keep a 34 year old zone system working great. I changed out the old trop-a-temp control panel with a honeywell hz-322k last year, the wiring was a direct replacement and with the dampers working again my two stage heat and cooling will continue to save money. As an fyi - took the dampers out and cleaned with denatured alcohol and they now work smoothly with the new mst.
