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Converting sngle-speed HVAC to multi-speed?

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  • Sep 2nd, 2019 12:06 am
[OP]
Deal Fanatic
Jul 7, 2017
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SW corner of the cou…

Converting sngle-speed HVAC to multi-speed?

Just wondering if the RFD HVAC pros know of any gizmos to turn a single-speed air handler to multi-speed?

I have a heat pump air handler that is only single speed (only one speed tap) which has been retrofitted with a 5 speed ECM motor.

I am guessing that I could put the speed tap on medium low (it's currently at medium, the default choice for a (stock/OEM) 3-speed PSC motor), or, once I find one, install a 5-speed manual selector switch. I find that the heating function could work on a lower speed on a cold winter day as it isn't getting that much heat and a slower speed through the evaporator may well be more efficient.

I did come across this product but it does come with its own ECM motor which does not use the speed taps as mine does (Mars Azure). The nice feature of this product is that is measures output air temp.

Are there any similar products that work with a Mars Azure?
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7 replies
Sr. Member
Jan 19, 2013
578 posts
365 upvotes
Ottawa
Decreasing airflow in heating will make the air more warm(comfortable) but make it less efficient.
Can be done with a simple relay to switch speeds
[OP]
Deal Fanatic
Jul 7, 2017
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SW corner of the cou…
1chinaman wrote: Decreasing airflow in heating will make the air more warm(comfortable) but make it less efficient.
True but I wonder on a cold day when the HP isn't extracting much heat weather a lower fan speed would suffice (i.e., a lower fan speed will extract as much heat out of the evaporator coil as the higher/normal speed). I understand that a higher fan speed is desired for cooling applications and the default "medium" speed is a compromise for heating and cooling, the latter we hardly ever use.

Price of the Fanhandler ECM kits are over US$500 which I think makes it less attractive given the age of my HP (~15 years).

Can you give me the schematics for the relay switch or do I just need 5 relays and a switch that can handle 24 VAC?
I smile when I see container ships sailing past my house laden with stuff made in China
Deal Guru
Feb 9, 2006
12325 posts
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Brampton
That motor looks likes a lot of like an azure motor. Have you contacted them to ask if their product will work with the digi-motor.

The upside of using the digi-motor is that in theory is it should be hard to fry as you can power multiple taps at the same time and it'll just go to the highest tap currently active vs a PSC if you power multiple taps it lets out magic smoke.
[OP]
Deal Fanatic
Jul 7, 2017
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SW corner of the cou…
tebore wrote: That motor looks likes a lot of like an azure motor. Have you contacted them to ask if their product will work with the digi-motor.
I did. The motor speed is set via a single low-voltage wire from the controller (Mars Azure speed taps (5) take 115VAC). Fanhandler claims their fan can turn as low as 200 rpm vs a minimum 625 rpm for a Mars Azure.

I guess the shell and other hardware of the motor may come from the same source but the electronics inside are different.
The upside of using the digi-motor is that in theory is it should be hard to fry as you can power multiple taps at the same time and it'll just go to the highest tap currently active vs a PSC if you power multiple taps it lets out magic smoke.
I managed to fry the 1st Azure motor, and it would look like it was defective. Had the motor configured and hooked up correctly (set for 230V, so just the wire to the live (L1/L2), ground and high speed tap. Worked fine. Then connected the training wire to the 24V. Came on, ran 30 seconds (seems it should have run at least 1-2 minutes). Stopped. And did nothing. So I took off the training wire, tried the speed taps. Nothing. Finally got to the low speed tap and... arc of spark and lots of smoke.....
I smile when I see container ships sailing past my house laden with stuff made in China
Sr. Member
Jan 19, 2013
578 posts
365 upvotes
Ottawa
thriftshopper wrote: True but I wonder on a cold day when the HP isn't extracting much heat weather a lower fan speed would suffice (i.e., a lower fan speed will extract as much heat out of the evaporator coil as the higher/normal speed). I understand that a higher fan speed is desired for cooling applications and the default "medium" speed is a compromise for heating and cooling, the latter we hardly ever use.

Price of the Fanhandler ECM kits are over US$500 which I think makes it less attractive given the age of my HP (~15 years).

Can you give me the schematics for the relay switch or do I just need 5 relays and a switch that can handle 24 VAC?
Lower fan speed in heat will extract less heat out of system.
Will send schematic to pm
[OP]
Deal Fanatic
Jul 7, 2017
6649 posts
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SW corner of the cou…
1chinaman wrote: Lower fan speed in heat will extract less heat out of system.
Will send schematic to pm
Thanks for the schematics. What should be aiming for (differential between output and input air, and/or differential between warm coolant from compressor and cool coolant to compressor?)
I smile when I see container ships sailing past my house laden with stuff made in China
Sr. Member
Jan 19, 2013
578 posts
365 upvotes
Ottawa
thriftshopper wrote: Thanks for the schematics. What should be aiming for (differential between output and input air, and/or differential between warm coolant from compressor and cool coolant to compressor?)
Depends on outdoor and indoor conditions.

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