ECM “Emergency” Motor Replacement

As I promised, since the world did not end on 12/21/12 with the end of the Mayan calendar, here is my first post of the NEW YEAR.

Simple Scenario —– Here it is the middle of the night — it’s 10 degrees outside and it’s a weekend and you are on a “no heat call” and find the ECM motor module has failed.  As you know from my previous posts on ECM motors, you need to get a correctly programmed motor for this unit and you don’t have it on your truck.  What do you do?  You need to keep the house from freezing (and your customer too).

Believe it or not, you can put in a PSC motor temporarily to give your customer heat until you get a new correctly programmed ECM motor from your supplier. (You can keep a “used” 1/2 HP motor in your truck stock just for this purpose).  You need to pull the ECM motor out of the unit and unplug the 5 pin power plug and 16 pin control harness. Don’t cut any wires because you’ll need these when you put the correct ECM motor back into the unit once you get it from your supplier.

Mount the PSC motor into the cradle and attach the blower wheel.  Now, you have one of  2 choices to make — do I run the fan continuous or do I create an intermittent fan operation to function like a standard furnace?

The first option is the easiest to accomplish. Simply run the power wires from the motor back to the power coming into the furnace.  The fan will run 24/7 and the heat will cycle off and on from the thermostat.

But what do you do if your customer objects to having the fan run all the time?  They feel it is too drafty or they don’t like to feel to “cold air” coming out of the registers.  The easiest solution is to add a simple single pole single throw relay into the power wiring to the motor.  Now, depending on the control board in the furnace, you power the coil off the EAC (air cleaner) terminals on the control board.  Most control board use a 110 VAC power off these terminals but some may use 24 VAC so you need to check the output from these terminals.  If these terminals are 110 VAC, you wire the coil of a 110 VAC relay to these terminal.  DO NOT wire the motor directly to these terminal since most of these will only handle 1 amp and the motor draws a lot more than that. Use the relay as an isolating relay to protect the board (or you will be replacing the board on a “call back” the same night).

Since the EAC terminals are powered any time there is a call for either heat, cool, or continuous fan operation, the relay is energized with the call and de-energized when the call ends giving the home owner an intermittent fan operation.  Here is a simple wiring diagram for accomplishing this:

ECM Emergency Motor Replacement1

The motor will now cycle with any call from the thermostat or control board.

Now, when you come back with the new ECM motor, you disconnect the relay, remove the PSC motor, and re-mount the ECM motor in the cradle and attach the blower wheel. Since you just un-plugged all the harness, now you just need to  plug all the harnesses back into the new motor and you’re back in business and you look like a hero to your customer.

Keep in mind that this also works for cooling in the summer!

About yorkcentraltechtalk

I have been in the HVAC industry most of my life. I worked 25 years for contractors on anything from residential to large commercial boilers and power burners. For the past 23+ years I had been employed by York International UPG Division ( a division of Johnson Controls) as a Technical support/Service Manager but I am now retired. One of my goals has always been to "educate" dealers and contractors. The reason for starting this blog was to share some knowledge, thoughts, ideas, etc with anyone who takes the time to read it. The contents of this blog are my own opinions, thoughts, experiences and should not be construed as those of Johnson Controls York UPG in any way. I hope you find this a help. I always welcome comments and suggestions for postings and will do my best to address any thoughts, questions, or topics you may want to hear about. Thanks for taking the time to read my postings! Mike Bishop
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10 Responses to ECM “Emergency” Motor Replacement

  1. Andy says:

    Doesn’t the PSC motor also require a capacitor?

  2. darrell says:

    Hello..i tried that on a Carrier model 58cva110 connecting a PSC motor using a relay to the EAC terminal

    it seemed to work with the cooling and continuous fan operation but during the heat cycle the burners stays on (blower on) for less then a minute then shuts off. the blower will continue to run for a few seconds then also shuts down.

    the heat cycle will start again and repeat the same sequences one more time but this time the furnace shuts down completely.

    the code LED flashes a 15 code indicating blower motor lock out..per the code description.
    it will remain locked out (furnace shut down) for 3 hours and start the cycles again..

    can anything be done to “fool” the CPU into “thinking” it has a ECM blower?

    or perhaps some other idea to make this work.

    thanks in advance

    • my suggestion would be to contact Carrier. The cpu may be looking for a “feed back” from their ECM to keep the heat blower running. Most controls do not look for this but Carrier may have this as a proprietary. sequence and only they could say haw to get around it if possible

  3. Joseph Blackstone says:

    Does the Frigidaire Model # R6GD-X36K072C (A Nordyne product) have that feed back property on cpu. The blower was replaced during a/c season and x13 replaced with standard blower with relay on a/c and sequencer for heat.Apparently the inducer motor run all the time from that point. They put a relay on inducer motor, but after heat cycles off and when comes back on it locks out on vacuum psi switch saying psi switch stuck on. Can pull wire off psi switch and put back on and goes through cycle. Then does the same thing when cycling back on. By not having the x13 blower is it locking out the control board on heat mode.

  4. Luis says:

    Thank you for posting this, I’ll save the wiring diagram in my cellphone. I’m sure I will be using it this summer.

  5. Peter says:

    Thanks for this interesting read. Do you have an article on a permanent conversion to a PSC blower? Carrier Infinity with a failed 3.0 ECM module and I’m looking for a cost efficient and permanent fix vs taking a chance and putting another very expensive module in. I would think a new, simpler ‘stat would be needed.

    • Unfortunately, I am unfamiliar with the Carrier Infinity. That is their “top of the line” product. I would suggest getting ahold of your local Carrier distributor for technical assistance on this.

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