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  1. #1

    New System with Variable Speed Blower

    Hello,
    I just had a new Bryant system put in our home. And the variable speed doesn't seem to work. It just blows full speed for a while and then shuts completely off.

    Here's the components:
    - Evolution 80v plus 315 VS Furnace
    - 116 Legacy AC
    - and a Preferred T-stat

    We got the VS because the salesman said it would help with our humidity problem. And the feature was promised to provide some efficiency benefit as well. My understanding was the VS blower ramps up and down to and from full speed. This was confirmed by the sales rep (he's the good cop). But when the owner came to look at it (he may be the bad cop) he said the system was working properly, just not the way I wanted, and he would look into it.

    By his response, and the prodding I've had to do to get other repairs made, I'm worried how things might turn out, and I was disappointed that I couldn't get support directly from the manufacturer.

    I'm hoping someone here might have some good advice. One question I had was if the Preferred T-stat isn't appropriate for the Evolution furnace? Thanks in advance for any comments, I appreciate having this forum to try out.

    Steve

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    Post the full model number. And if you know what size your old furnace was, post that also. Along with the size of your house, and location.

    Could be that your new furnace is over sized. And that your duct system is too small to handle the air that it needs to move.
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    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,371
    You won't necessarily notice the blower ramping up and down throughout the cooling cycle. It will do this as necessary to maintain CFM, but probably not noticeable. Not sure what you were told when you were sold the v/s furnace. It may have a slow ramp-up feature in the cooling mode (as Trane does), but as far as adjusting it's speed throughout the cycle to a noticeable degree, that typically doesn't happen. However, if you have the Performance thermidistat, it should be configured so that it does slow the blower down to control humidity (in the cooling season) -- to about 80% airflow. Depends on the thermostat you have and how the installer set it up. It could be that your system is working correctly, and that you were not fully informed how the system would operate. Variable speed means that the blower is electronically controlled in such a way that the motor will adjust RPM, as necessary, to maintain an exact CFM (as pre-selected by the installer). It also means, as you think, that it will control its speed when dehumidification is needed. This depends the thermostat, and the control board (dipswitch) settings.

    I think you have the "good cop" and the "bad cop" reversed.

  4. #4
    Join Date
    Aug 2009
    Location
    NW FL
    Posts
    176

    3.5 ton calculation, but heat pumps come in whole tons

    What do you do when an HVAC contractor calculates a 3.5 ton and the models you are interested in are available in 2, 3, 4, and 5 tons?

  5. #5
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,039
    Quote Originally Posted by RoseRx View Post
    What do you do when an HVAC contractor calculates a 3.5 ton and the models you are interested in are available in 2, 3, 4, and 5 tons?
    You get the 4 ton 2 stage Rose. In Lo stage it will be a rougly a 3ton.

    Oh- and make sure ducts can handle the Hi stage air flow or you will have problem this OP may have.

  6. #6
    Thanks for the responses,
    here's the specifics:
    3.5 ton
    in an old 1500sqft in Little Rock that used to have a leaking 4 ton.
    315AAV060110AFJA Furnace
    116BNA042000BAAA Condenser
    CNPVT4821ATAACAA Coil

    And yeah, if I just imagined the v/s different that it actually is, I can accept that. But when it's working it seems to cycle on and off fairly often (maybe 15 mins) and I just suspected that would have been different with the v/s. Is there any further info that might shed light on this?

    Thanks again for the input.

  7. #7
    And on the ducts. We had the same installer put in all new ductwork. I hope he put in what was needed.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,913
    Big furnace for 1500 sq ft. Sounds like under sized duct work.
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    How-to-apply-for-Professional

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

  9. #9
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,039
    Is that a single stage furnace

  10. #10
    Join Date
    Jun 2007
    Location
    Round Rock
    Posts
    3,550
    Without the communicating thermostat. You basically have a 2 speed motor on the furnace. It more or less runs at high or low. You have to set the thermostat and dip switches on the furnace correctly for it to work somewhat correctly. It looks like you have too much a/c for your house. 3.5 tons is too big even for rule of thumb sizing, that is unless you live in a glass house with no insulation.
    I like DIY'ers. They pay better to fix.

  11. #11
    Would the system work better with the Evolution thermostat? Is that more appropriate?
    Thanks

  12. #12
    No, it's a two-stage according to the brochure. I was just re-reading it and it says this furnace "runs nearly continuously at a very low speed". That's not my experience so far. It's always full speed or off.

  13. #13
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,039
    Hmm ask the contractor to show you the difference in Lo and Hi stage then.

    Makes sure its set up right.

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