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.

Fan Coil with ECM Motor

I have been called to a job that has 2 Bryant air handlers

with ECM motors.  The home owner has just

replaced the Trianco Heat Maker with Crown Bimini and a 40 gal. mega-stor.  The homeowner did a fairly nice job of piping

the boiler according to the instructions. 

The problem is the existing air handlers are set up with Honeywell strap

on aquastat (L4009C) to make on temperature rise and close R to G on the air

handler.  In other words when the coil

gets hot the blower motor operates.  This

works fairly well with PSC motors, but with the ECM motor, the blower operates

at only 20 to 30% of full speed (more or less) if there is no other call for

heat or cool.  Customer complains there

is not enough heat on the second floor zone. 


Has anyone retrofitted a fan coil to a cooling only air

handler with ECM motor?  What control or

wiring ideas have worked?


I will figure this out, but I don’t want to spend time

re-inventing the wheel if there is one already out there.


Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics


  • Ironman
    Ironman Member Posts: 7,119
    ECM Motor

    Is the cond. unit single stage? If so, connect "Y" from the thermostat to "Y2" on the AHU. Then jumper "G & Y1" together at the AHU. You'll get about 66% of full speed for heating.

    Note: there should be an isolation relay to break "G" between the thermostat and aquastat or else it will back feed to "Y" at the thermostat an bring the compressor on when the aquastat closes.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • geno54
    geno54 Member Posts: 43
    Hydro air controls

    Model number of Air handler please and a schematic if possible. It can be done but would have to add a 3 pole relay. Don't know of anything off the shelf for hydroair and ECM motors.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 5,628
    edited January 2011
    The case of the Variable Speed Air Handler and the Duct coil

    My previous customer was helped by your suggestion and a little help form others.  It turns out that the ECM motor DC Controller was defective along with other issues. 

    New problem:  Have Hydronic coil on another system.  Replacing air handler(AH) with 16SEER Cond unit.  Must use variable speed AH to get proper match. Without a heating relay (usually supplied with the electric heat kit), how do I get the Blower to operate at a proper speed for heating?  This time I can't use Y2 because the outdoor unit is 2 speed.

    The thermostat has RH and RC terminals  Y1 and Y2   G    W1 and W2 and a  B (common)

    The air handler has:  (R)    (BK)  (Y)     (Y lo)       (G)      (O)     (B) Common   (W1)  (W2)  and (W3) 

    American Standard 4TEE3F31B1000B,

    The old system used an aqua-stat to bring on the air handler fan.  RH and W from thermostat to bring on the zone valve then the ZV end switch to bring on the boiler.

    You would think that someone would have a simple (stupid proof) control that could easily retrofit to most ECM air handlers to get the most efficient fan speed and coil temperature combination.
    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
This discussion has been closed.