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  1. #1
    Join Date
    Nov 2003
    Posts
    15

    Variable Speed Air Handler only runs in hi-blow?

    Hey gang-

    We just got a new Carrier Heat Pump (25HCC5) and Variable Speed Air Handler (FV4C). Professionally installed with the Carrier Programmable Edge Thermidistat.

    Our initial observation is that if there is any "variable speed", we sure haven't seen or heard it. The unit seems to be always blowing in one very high (and rather loud) speed. This is just my observation as the home-owner, but I'm 99% sure. I would expect this if I was demanding a large temperature change, but this is still the case even when the room has been stabilized for some time at the desired temp.

    I do see one possible issue- but wanted to run it by you experts first. I cycled through the Configuration mode on the Thermidistat, and Option 41 (Variable Speed Blower) is set to the factory default of Off. I wanted to make sure this setting is referring to the Air Handler blower and not the Heat Pump blower before I changed anything.

    Humidity in the room has been consistently below the Set point, so I don't believe there is any Dehumidification demand going on.

    Ideas or other things to check? Just when should I go seeing some "lower speed" fan operation?

    Thanks!

    Kupe

  2. #2
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,046
    You have only one blower motor. The variable speed if enabled would take place in the first 8 minutes of on time and depending on configuration could drop to 50% of selected output for fan in the on position

  3. #3
    Join Date
    Jan 2008
    Posts
    1,858
    I would politely ask the installer to come over and explain and review each parameter on that thermostat, and make sure the air handler and stat are set correctly. You could cause problems if you change the wrong setting.
    Also, since you said it was rather loud, I would ask him to verify proper cfm settings.
    "Hey Lama, hey, how about a little something, you know, for the effort." And he says, "there won't be any money, but when you die, on your deathbed, you will receive total consciousness." So I got that goin' for me, which is nice. - Carl Spackler

  4. #4
    Join Date
    Jun 2011
    Location
    Wake Forest, NC
    Posts
    352
    Even when it is operating on "high" it should not be noticably loud. Either your ductwork is undersized for the unit or the speed taps were not properly set on installation. When your pro returns to check the settings on the thermostat it would not be a bad idea to have them verify the speed tap settings on the board to make sure it is not running higher than it should.
    It's not rocket-science...

    It's electromechanical thermodynamic engineering

  5. #5
    Join Date
    May 2011
    Location
    Fort Worth, Texas
    Posts
    49

    Undersized Ventilation

    I'm in agreement with HVACTechNC! I think your SA or RA ventilation is undersized. I don't know enough about speed tap settings to provide any intelligent input. Noise from AHU is caused by high velocity/high friction. (Undersized ventilation) JMO

  6. #6
    Join Date
    Nov 2003
    Posts
    15
    Quote Originally Posted by second opinion View Post
    The variable speed if enabled would take place in the first 8 minutes of on time and depending on configuration could drop to 50% of selected output for fan in the on position
    Thanks! So initially it would always come on in "hi blow"?

    Any thoughts on where else to look to see if Variable Speed might be disabled? I strongly suspect that Thermidistat Option 41 might be incorrect. But I will run this by my installer as we have a small punch list of items.

    Kupe

  7. #7
    Join Date
    Jun 2011
    Location
    Wake Forest, NC
    Posts
    352
    No, normally the system would come on in "low" with the compressor on stage one. If the heat load cannot be satisfied within a time determined by the processor of the thermostat/control board it ramps up to high and engages stage 2 on the compressor. If a two stage system with a variable speed fan consistently starts in stage two with the fan on high it is a good bet the controls and speed taps were not configured properly.
    It's not rocket-science...

    It's electromechanical thermodynamic engineering

  8. #8
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,046
    Have them verify system set up for you. You are on the right track but there is other configurations that need to be set.

  9. #9
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,375
    Quote Originally Posted by HVACTechNC View Post
    No, normally the system would come on in "low" with the compressor on stage one.

    Only flaw is this is a single stage unit.

    Does Carrier have a Comfort-R type ramp up?

    Sounds like the OP may be on to something with VS turned off at the Infinity control. They should be able to adjust constant airflow with the control.

  10. #10
    Join Date
    Nov 2003
    Posts
    15
    Quote Originally Posted by BaldLoonie View Post
    Only flaw is this is a single stage unit.

    Does Carrier have a Comfort-R type ramp up?

    Sounds like the OP may be on to something with VS turned off at the Infinity control. They should be able to adjust constant airflow with the control.
    Yes- Single Stage Heat Pump, Variable Speed Air Handler. I'm convinced the Air Handler is only running in high-blow and that is the issue I will pursue with the installer.

    I'll post what I learn.

    Kupe

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