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Old 01-20-2011, 11:34 AM   #1
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Lennox Fan - Low Speed Only?


I just installed an Elite G61MPV-60-91 furnace and a Signature XC21-048 air conditioner with a ComfortSense 7000 thermostat. I have a two-story colonial home and a finished basement and have only the one system. When the fan is set to ON it runs at a low speed between heating cycles (38% of full speed Iím told), just barely circulating air. Itís winter here in Maryland so that is not a particular problem. However in the summer I want the fan to run at high speed between cooling cycles circulating air from the cooler lower floors to the upper floor. My installer tells me that between cycles the fan will not run at high speed, only at low speed.

Is this correct? If so, why? It has been my experience that in multi-story homes with one system the fan needs to run constantly at a high speed to keep the upper floor cool.

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Old 01-20-2011, 02:32 PM   #2
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Lennox Fan - Low Speed Only?


The combo settings of t-stat are probably lower fan speeds when in heat mode and highest speed setting when in cool/AC mode.

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Old 01-20-2011, 03:12 PM   #3
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Lennox Fan - Low Speed Only?


Its so that you get a less noticeable air flow, so that you don't hear the air noise, nor feel like warm air is blowing on you in summer.

Also. In summer, you should use recirc instead of fan on. Using fan on tends to raise the humidity level in your home by re-evaporating the water off of the cooling coil.

With the XC21, you should have a problem with needing to run the fan to even out house temps, since if its sized right, it will spend a lot of time running in first stage.
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Old 01-20-2011, 04:06 PM   #4
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Lennox Fan - Low Speed Only?


Thanks BeenThere,

The XC21 replaced a 15-year-old unit and I'm anticipating rather than knowing what the effect will be this summer. I ran the fan on the old unit 24-7 to keep the upstairs relatively cool and have done the same thing in other 2-story homes I've owned. I'm having a hard time believing that with only one unit the upstairs will stay as cool as necessary if the fan is not circulating a lot of air off-cycle. However I guess I'll just have to wait and see.
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Old 01-20-2011, 05:00 PM   #5
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Lennox Fan - Low Speed Only?


The upstairs won't be perfect. but should be more then acceptable.
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Old 01-20-2011, 05:47 PM   #6
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Lennox Fan - Low Speed Only?


If I remember correctly hooking G from the stat to Y1 on the control board will do what you want. Of course Y1 from the stat will have to go to Y1 on the AC via a wire nut instead of the furnace control board. That should give you roughly 1100 cfm on continous instead of 600.
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Old 01-20-2011, 06:13 PM   #7
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Lennox Fan - Low Speed Only?


Actually it needs the Y1 wire on the board to energize the 1st stage cooling fan speed and set it properly (will affect the approach temp readings if not correct) and a Y2 for second stage. There is no workaround that I know of.
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Old 01-20-2011, 06:35 PM   #8
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Lennox Fan - Low Speed Only?


Last summer we had one that wanted higher cfm for contious and that's what tech support came up with. The stat will energize G which will power up Y1 on the board on either a first stage cool call or a continous fan call.
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Old 01-20-2011, 06:42 PM   #9
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Lennox Fan - Low Speed Only?


If he turns the fan to ON and it energizes Y1 it will run it at 1st stage cooling speed (that does make sense now). It may be drafty and noisy in the Winter and Summer though. Y2 signal will switch it to the necessary high speed. Will lose his ramping profile but that is not a big deal anyway. Would confuse the heck out of any service guy who later goes to change the board. I would want a sticker with a clear description of why it was wired that way for them. Had a reverse scenario with a G71-70 with a 3 ton blower and a 1.5 ton AC. Minimum fan CFM even with the Dip switches set for 15% less is still too high. Cut the jumper between Y1 and Y2 ( for 2 stage use on the board) and use Y1 and it fools it into using a lower fan speed more suitable for a 1.5 ton.
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Old 01-20-2011, 06:49 PM   #10
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Lennox Fan - Low Speed Only?


That's the only issue with my set up. The dang three ton blower on a 45K G61 doesn't go low enough to dehumidify first stage cooling. It's only running less then 16,000 BTU on first stage and the blower wont go below 600 cfm. Sure wish it came with a 2 ton blower that could be set down to 400 cfm for first stage.
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Old 01-20-2011, 06:56 PM   #11
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Yep. Seems like they think everyone needs a 3 ton blower and unit for a 1000 sq ft bungalow. We all don't live in hot humid climates like Florida. Trivia, there are as many people in hot California as in Canada so who cares about a few miserable Canucks or northern folks when the bulk of your clients are in the hot States. They design everything for max AC use and them.

The G71 and SLP have more fan adjustments. Can run the continuos on 100% with a Dip switch change.
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Old 07-07-2012, 12:35 AM   #12
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Lennox Fan - Low Speed Only?


Marty S. wrote:
If I remember correctly hooking G from the stat to Y1 on the control board will do what you want. Of course Y1 from the stat will have to go to Y1 on the AC via a wire nut instead of the furnace control board. That should give you roughly 1100 cfm on continous instead of 600.

------
I'm having the same problem, I'd like to run the fan at higher speed.
I see the G and Y1 wires from stat to control board, but where is the Y1 wire to the AC? I see 2 yellows in a plug connector on the lower right of the control board, is it one of those?

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