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Old 08-14-2009, 12:41 PM   #1
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Is there a way to have heat, cool and fan all on same blower speed?


My furnace control board has 2 park (M1 & M2), 1 heat, 1 cool, 1 h/c, and 1 fan connections. Currently, I have med low on h/c and low on fan. I've measured my ESP and my heat rise and have determined that I could be running heat and cool on the lowest speed. I'd also like to have the fan run on the lowest speed. Is there any way to do this?

Another question: I have a 2 stage furnace, so does the first stage run on "fan" speed or "heat" speed?


Last edited by pirateo; 08-14-2009 at 12:45 PM.
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Old 08-14-2009, 01:47 PM   #2
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Is there a way to have heat, cool and fan all on same blower speed?


You can always splice the low fan terminal to one or more of your board terminals. But just to be sure you understand your system I would run it through all its modes (heat, cool (each stage) and fan) to see what's energized when. You might also want to contact the manufacturer to be sure since the last thing you want to do is ice up your indoor coil or overheat your heat exchange from air flow that is too low. It might also help you to debug it in case of future problems.

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Old 08-14-2009, 04:02 PM   #3
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Is there a way to have heat, cool and fan all on same blower speed?


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Originally Posted by dac122 View Post
You can always splice the low fan terminal to one or more of your board terminals. But just to be sure you understand your system I would run it through all its modes (heat, cool (each stage) and fan) to see what's energized when. You might also want to contact the manufacturer to be sure since the last thing you want to do is ice up your indoor coil or overheat your heat exchange from air flow that is too low. It might also help you to debug it in case of future problems.
Thanks. Just to follow up, I did test the heating in each stage and the 1st stage does indeed use the fan setting and the second stage goes to the heat setting. With the low setting on stage 2, my heat rise is 47.. range is 35-65. The low setting on stage 1, my heat rise is 34.. range is 25-55.

On the low setting, I'm getting esp of about .65 (down from .78 on med-low), which translates to about 1150 cfm per the product graph. I have a 3 ton a/c, so that should be okay. Delta T on cool is 21 on low with wet coil.

I guess I'll do the splicing.

Thanks.
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Old 08-14-2009, 04:04 PM   #4
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Is there a way to have heat, cool and fan all on same blower speed?


Delta t on cooling sounds acceptable. How are you measuring your static pressures, and where?
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Old 08-14-2009, 04:13 PM   #5
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Is there a way to have heat, cool and fan all on same blower speed?


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Delta t on cooling sounds acceptable. How are you measuring your static pressures, and where?
Measuring ESP negative side in the blower compartment after filter and positive through the limit access hole before the coil. The drop across the wet coil is .21.

Another question I have is, this furnace max wc static on nameplate is .50, which I'm assuming is without coil. Does that mean that I can subtract the .21 pressure drop across the coil from my .65?
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