Motor Speed


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Old 02-24-20, 06:11 AM
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Motor Speed

Good day. I have a Trane 3.5 ton heat pump. My fan just gave out in my air handler and when I went to install a new fan I noticed that it is a 3 speed motor but only wired to use one speed. Right now itís wired for low speed. Is it any gains or losses if I was to hook it up to med or high speeds or should I just leave it at low. My house is a 3 story and I was thinking if the speed was higher, more air flow would get to my top floor. Any thoughts?
 
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Old 02-24-20, 06:42 AM
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Do you have your air handler model number?

I think it's typical for air handler to have a nominal speed that can be adjusted +- 10% (using the jumpers on the board) depending on your duct work. The manual would explain exactly what the adjustments do.

Higher speeds means faster air so it could get more air through the register on longer runs, but it also means more noise and higher static pressures. Too high of a static pressure could lead premature equipment failure (fan has to work too hard to keep up airflow).

Someone who knows more can probably correct me, but I believe a higher airspeed will mean better transfer of heat at the coil which is better from an efficiency standpoint. However it may be worse from a comfort perspective (won't dehumidify as effectively in the summer, and lower air temperature at the registers in heating season). If you have an issue with some rooms getting too much airflow and others getting not enough, then the fan speed won't change the underlying issue. You may need to look into dampers or some duct work changes for that.

 
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Old 02-24-20, 09:18 AM
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Welcome to the forums.

As mentioned.... the air handler model number would be helpful.
From what I've come across..... it's rare to have an air handler for A/C running at slow speed.
Typically the slow speed is for the electric heat.
 
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Old 02-24-20, 11:48 AM
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The model number is C3F36B1000AA. The fan speed would not be changed with jumpers on this unit because the motor itself has 3 spades for different speeds, and mine was on the slow speed. It was wired that way. This heat pump is used 95% for heat. I vary rarely use AC because of the climate that I am in.
 
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Old 02-24-20, 11:56 AM
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So you are saying that your air handler has a three speed motor but only one speed wire going to the motor. Since it's being used mostly for heat..... it may need to be kept there. You may get more airflow on medium but not necessarily more heat.
 
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Old 02-24-20, 12:20 PM
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Yes that is correct. It was wired that way. I thought it might have to be left that way because no one has changed it since it was new. Thanks for the replies.
 
 

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