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Old 07-01-2020, 10:49 AM   #16
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Re: Slow down A/C Fan?


I appreciate the information. The thermostat does have the ability to monitor/control humidity, running the fan on low speed with the compressor on. However, I was told by the installer not to use this feature due to possible freeze up and compressor damage. I have never used/adjusted this function. The real solution, I think, is to allow the temperature in the house to climb 1 degree or so instead of the fraction of a degree now happening. The system would run longer and less frequently, but the thermostat installed (Honeywell 9000) does not allow that to be changed and I do not want to replace parts in a system still under warranty (parts and labor for 10 years).
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Old 07-01-2020, 11:36 AM   #17
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Re: Slow down A/C Fan?


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However, I was told by the installer not to use this feature due to possible freeze up and compressor damage.
Doesn't surprise me considering it's the same company that put a 110k furnace into a 2500 sq ft house.

If the unit is set up properly, this is not a concern.

Set up properly means doing testing and adjustments to make sure the coil doesn't drop to freezing and liquid refrigerant doesn't make its way back to the compressor.

Right now your airflow is way too high and just getting it down to 1200 cfm should make a big difference, you're probably getting very little dehumidification.

But the best of both would be allowing it up to 1400 cfm or so and dropping it down to dehumidify on demand. Works best when you have a txv type metering device on the coil.
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Old 07-01-2020, 12:36 PM   #18
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Re: Slow down A/C Fan?


One problem you may have is that even with the high speed slowed down 10% it will still be way too high.

There is a way to fool the circuit board into using the lower fan speed which is normally used in a 2 stage AC.

You will have to discuss this with your tech. I work on a lot of Lennox units and there are dozens of different boards etc so don't quote me exactly.

If you get your tech to tell the board to be setup for a 2 stage AC by flipping a dip switch it will start on low speed which is close to your 1200 cfm ( 1180 on stage one 1750 on 2nd stage high you have now) . He can then put the Y wire from your 1 stage AC to Y1 and the board will think you are running a 2 stage AC and won't go to the very high speed you have now. It needs a Y2 signal to do that and you have none.

If that works then you will get a lot lower fan speed and it should be safe as long as he checks the freon pressures and cooling temp of the air.

I would have to see the service manual and install manual plus your thermostat setup to quote you specifics but in theory this should work if he can understand it.
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Old 07-01-2020, 02:21 PM   #19
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Re: Slow down A/C Fan?


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Originally Posted by oldelectricguy View Post
I appreciate the information. The thermostat does have the ability to monitor/control humidity, running the fan on low speed with the compressor on. However, I was told by the installer not to use this feature due to possible freeze up and compressor damage. I have never used/adjusted this function. The real solution, I think, is to allow the temperature in the house to climb 1 degree or so instead of the fraction of a degree now happening. The system would run longer and less frequently, but the thermostat installed (Honeywell 9000) does not allow that to be changed and I do not want to replace parts in a system still under warranty (parts and labor for 10 years).

While allowing the temp to rise 1 degree or so before bring on the A/C will give you longer run times, and fewer run times. The also longer off times would allow more humidity to build up in the house.



I doubt your installer wired up the thermostat properly to use the blower slow down ability.
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Old 07-02-2020, 10:43 AM   #20
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Re: Slow down A/C Fan?


Wow, a lot to think about, particularly using a 'ghost' 2 stage compressor setting. As I said, a tech will be coming to perform a system check soon, and I will be talking to him about this. Many thanks. And yes, the 110K furnace was a 'big'surprise, as the agreed (and paid) upon one was 90K. This is not a condensing furnace, as the route for the intake/exhaust for one of those was too long/bendy. The previous furnaces were 90K.
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Old 07-02-2020, 11:06 AM   #21
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Re: Slow down A/C Fan?


^breach of contract and they should have put the right furnace - their mistake. you're not getting the real benefit of 2-stage.

Quote:
Wow, a lot to think about, particularly using a 'ghost' 2 stage compressor setting.
Not needed, it can be slowed down to 1260 cfm. Attached.
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Old 07-02-2020, 11:56 AM   #22
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Re: Slow down A/C Fan?


You can do the 1260 BUT it is easy to fool the board and get even better results with the 1050 and nothing will be harmed.

Only caution is to make sure you put a large sticker on the front door so if someone else replaces the board years later they know what positions to set all the switches in. Or else it will go to factory default.

It is possible to upsize the piping on a high efficiency furnace if the length of run is too long. If there is poor slope then you are up the creek.

You can also vent them up the chimney and use a elec water heater. Most of the time there is a way to install them.
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Old 07-02-2020, 02:48 PM   #23
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Re: Slow down A/C Fan?


Well, I had the 'too big' discussion and got a refund instead of a replacement. I am stuck with what I have now and I have no problems with the heating, only the short cycling on cooling. The fan speed chart for my furnace is slightly different from @user_12345a 's chart. I have circled the current settings - I have never changed them. My original idea was to drop the speeds 10%, or down 1 line in the chart.
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Old 07-02-2020, 03:17 PM   #24
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Re: Slow down A/C Fan?


If you want to use the first stage cooling chart and speeds you need to fool the board into thinking you have a 2 stage AC like I indicated earlier.

If you have a bigger house you may want 400 cfm/ton to get more air to the further rooms or if you want more humidity removal then use 350 cfm/ton. You have to pick one and give up the other a bit.
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Old 07-02-2020, 03:22 PM   #25
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Re: Slow down A/C Fan?


Drop it down to low, - adjustment to start with and see what happens.
-------------------
You can go 450+ cfm per ton and slow it down on demand - either humidistat or your thermostat. Some wiring changes required. Get the best of both.

The install manual should have details on wiring with dehumidify terminal and how much it turns down the blower.

I wouldn't go much below 350 cfm per ton in dehumidify mode.

Charge needs to be checked after these adjustments.
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Old 07-02-2020, 05:39 PM   #26
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Re: Slow down A/C Fan?


Configure it as a 2 stage, and just wire the board's Y1, to get a proper blower speed/CFM. 450 CFM per ton is not something to use in PA.
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Old 07-02-2020, 05:50 PM   #27
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Re: Slow down A/C Fan?


^Unless slow down to dehumidify is used - definitely not a good idea otherwise.
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Old 07-02-2020, 06:35 PM   #28
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Re: Slow down A/C Fan?


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Originally Posted by user_12345a View Post
^Unless slow down to dehumidify is used - definitely not a good idea otherwise.

Even if slow down to dehuhumidify is used, its not a good idea. As it would ten to just increase RH as soon as the slow down ended.
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