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Old 04-12-2012, 07:52 AM   #1
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Air Flow Switch Setting


I'm almost finished replacing my 3 ton heat pump's R4.2 flex with R8 hard pipe. Actually a combination hard and flex duct due to framing and plumbing waste line obstructions.

The 90 degree trunk takeoffs were replaced with 45 degree. In some areas I'm seeing a 200 fpm increase in air flow. I did install dampers for each room supply so I can adjust for optimum air flow.

Is there a problem with changing the air handler DIP switch setting that controls the fan speed? Right now its set at Med-High with a nominal air flow of 1100 fpm. The next setting is Med-Low at 900 fpm. The Med-High setting was probably selected at initial install to overcome the duct restrictions.

Is this a better option than closing off dampers too far to adjust room air flow?

Does changing the setting affect system R22 charge numbers?

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Old 04-12-2012, 09:26 PM   #2
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Air Flow Switch Setting


The furnace dip switch settings should be in CFM, not FPM. 900 CFM is a bit too low for a 3 ton unit. Most 3 ton heat pumps e set for 1200 CFM.

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Old 04-13-2012, 05:43 AM   #3
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Air Flow Switch Setting


Your are correct Sir. I mis-typed. Should be 1100 CFM. That number is off the performance data sheet and is reduced since heat strips are installed.

So the correct procedure is to adjust each rooms airflow with the damper.
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Old 04-13-2012, 03:40 PM   #4
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Quote:
Originally Posted by Earnie View Post
Your are correct Sir. I mis-typed. Should be 1100 CFM. That number is off the performance data sheet and is reduced since heat strips are installed.

So the correct procedure is to adjust each rooms airflow with the damper.
Yes, thats the best way.
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