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  1. #1
    Join Date
    Jul 2010
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    9

    Trane Hyperion AH low spped fan

    I just had a new Trane AC system installed with a GAF2A0A36M31SA air handler. My thermostat has a dehumidify feature for low speed AC fan. I would like to know if this air handler has a low speed fan option and if so how it should be hooked up.
    Thanks

  2. #2
    Join Date
    Aug 2010
    Location
    West Monroe, LA
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    1,537
    The GAF air handler has a fixed speed motor. It does however have speed taps to raise or lower the fan speed to match the outdoor unit cfm as this air handler has several outdoor units that it will work with.

    As far the humdity setting on your t-stat with that air handler I would not use these feature. The reason being it is not variable speed so the fan does not have the ability to ramp up or down. It just has the speed taps to select from.

    So once the heat or air comes in it will run at one fixed speed that the installer set it up for. If you used the humdity control feature on the t-stat with that unit it would just keep the outside unit running and the indoor fan would stay on but at the speed selected. This can lead to increased electic usage in trying to do so.

    Know if you had say a tam7 variable speed air handler with any outdoor unit and humdity control feature is selected. Then once the unit researched the temp that t-stat is set for but the humdity level is not meet. The outdoor unit would stay on along with indoor unit. Indoor unit will depending on wiring and how it is set up. It would adjust the fan speed to say 50% of the rated cfm selected for the unit. This allows the air handler to move cooler air across the coil but at a lower speed in turn letting it dehumdify better.

    Again with that air handled I would not select the humdity feature as it is not designed to be used that way. Are you having humdity problems in your home? If so the fan speed might be able to be lowered to less cfm with the speed taps. Bare in mind this needs to be done by your installer as he will know the lowest the amount of air flow that your system can be lowered to for the system to work properly.

  3. #3
    Join Date
    May 2009
    Location
    Cummins, GA
    Posts
    1,563
    What thermostat do you have?

    On 90% of thermostats; If you enable the dehum option with that AHU, your thermostat will over cool to remove the moisture from the air. The max is 3 degrees.

    This will get the job done...just not very efficiently.

    As stated above, a variable speed blower is optimal for dehumification.

  4. #4
    Join Date
    Jul 2010
    Posts
    9
    Thanks for the responses. I am aware of the preference for variable speed fans, the problem is that I could not use the TAM7 because it is too big for my AC closet. The GAF2 was the only air handler that would fit. My old Trane air handler had the variable speed fan, which I really liked, but sadly they make them bigger now. I saw in the circuit diagram an idication of low and high fan speed, so I thought maybe there would be a way to select the low speed when running for dehumidify only. My thermostat will dehumidify with high speed fan but it gets too cold. BTW, I am using a Honeywell Prestige thermostat. FYI, the reason this is an issue is because I live in South Florida and use AC year round. In the winter the humidity tends to climb due infrequent running of AC.

  5. #5
    Join Date
    Aug 2010
    Location
    West Monroe, LA
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    1,537
    Know I am curious. What size closet do you have? If you had a a (3) ton variable speed older air handler it should have been 21.5-23.5 wide with 22" deep by 43-45"
    Tall? Depending on your new system outdoor size and type (a/c or heat pump) a tam7030 air handler could have been used.

    Which comes in at a little over 21" wide same depth but 56" tall. I have yet to run into a air handler closet that we couldn't retrofit the new air handler to work in. Closet door frame might have to be pulled or platform lowered. While lowering the platform can cause decreased return air In which I have been able to add another return.

    I am lot saying your installer could have made it fit but that sometimes we have to think outside the box. All air handlers have gotten bigger due eff. Reasons.

    Sorry got off topic. Again I would suggest with your t-stat not to run humdity feature on the t-stat due to the GAF air handler not being able to slow the blower speed down. As you stated it will over cool same as it would still due with variable speed air handler but would remove more humdity then a fixed speed motor that knows one speed.

    I see you are in Florida. So you have more humdity then someone home that is up north same as our climate in Louisiana. Did your installing company run a load cal. On your home before installing the equipment? Proper sized system should run more often to remove humdity. While a oversized system will run long enough to reach the t-stats set point then shut off and back on again in a short time. Since the system has already been installed if you have humdity problems might want to call them back out to review over the system. Also you can look at having a dehumditfer installed to work with your system.

  6. #6
    Join Date
    Jul 2010
    Posts
    9
    You are correct regarding the size of my old unit. Your assumption regarding the size of the new variable speed handler is also correct. The problem is that the ceiling is 55 inches from the platform, 1 inch too low also leaving no room to connect to the ductwork. The problem is that the platform cannot be lowered because there is a hot water heater under it and it also is very tight. My installer and I went over this at length and there was no option short of major reconstruction which I was not prepared to do. As far as a system sizing, he did this when he installed the previous system 17 years ago and the old system worked very well all that time. Since the humidity issue only occurs during the winter months I will just have to live with it.
    Thanks for your interest, I was just fishing for an alternative.

  7. #7
    Join Date
    Aug 2010
    Location
    West Monroe, LA
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    1,537
    Quote Originally Posted by sorapp View Post
    You are correct regarding the size of my old unit. Your assumption regarding the size of the new variable speed handler is also correct. The problem is that the ceiling is 55 inches from the platform, 1 inch too low also leaving no room to connect to the ductwork. The problem is that the platform cannot be lowered because there is a hot water heater under it and it also is very tight. My installer and I went over this at length and there was no option short of major reconstruction which I was not prepared to do. As far as a system sizing, he did this when he installed the previous system 17 years ago and the old system worked very well all that time. Since the humidity issue only occurs during the winter months I will just have to live with it.
    Thanks for your interest, I was just fishing for an alternative.
    Well that makes perfect since then on why your installer could not install a variable speed air handler.

    So your humdity problem is in the winter? Is it too high or low? Normally the only issue I have seen with humdity during heating season is that it is too low. If this is the case humdity control will not help.

    If you are having high humdity in the winter months there might be something else going on with the system depending on how you run it? What is the humdity level in the home when you are having the problem?

  8. #8
    Join Date
    Jul 2010
    Posts
    9
    I use the A/C in the winter specifically for cooling since it is often quite warm in So. Florida, and of course there is humidity along with it. Since the temp is not as high as in summer the A/C cools the house quickly leaving the humidity to accumulate. This is not a severe problem, more of a nuisance, which is why I chose not to go the expense of a separate dehumidifier.

  9. #9
    Join Date
    Jan 2004
    Location
    PA
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    68,795
    Is the outdoor unit/condense also a 3 ton unit.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #10
    Join Date
    Jul 2006
    Location
    Virginia
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    4,903
    your installer can add a relay to lower the fan speed
    We really need change now

  11. #11
    Join Date
    Aug 2010
    Location
    West Monroe, LA
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    I think will also ask if the outdoor is a (3) ton like Beenthere has. If it is not a set up for factory setting of (3) ton your installed should be able to adjust the speed tap down without causing problems if you have (2.5) ton unit.

    While this help if the cause with no cooling demand the unit will still run till the t-stat temp is reached. While lowering the fan speed if the installer can will allow the unit to run longer with lower cfm. On cool days when cooling full load is not needed you still see the same but lowering the fan speed again might help.

    What is the humidity in your home right now? As you have noted humidity is the key to comfort not temp in most cases...

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