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New to heat pumps. Air handler at full throttle with no heat.

Rob94hawk
Rob94hawk Member Posts: 20
in A-C, Heat Pumps & Refrigeration

My new Bosch Heat pump
Outdoor model: BOVB-60HDN1-M20G
Indoor model: BVA-48WN1-M20

So every so often the air handler blows air at full throttle with no heat and the outside compressor isn't running. It will run like this for a few minutes till it throttles down, compressor goes on, and then heat comes out.

Is there a reason for this? Thanks

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 25,311

    Defrost cycle

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • pecmsg
    pecmsg Member Posts: 5,545

    I thought Defrost was low speed?

  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 9,745

    Without looking at the manual, I would think that is not a normal operating procedure. I would call the installing contractor and voice your concerns.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • bburd
    bburd Member Posts: 1,097

    Wouldn't the compressor be running in reverse in defrost, and the back up heat also on at the same time?

    —
    Bburd
  • Rob94hawk
    Rob94hawk Member Posts: 20
    https://forum.heatinghelp.com/discussion/comment/1824924#Comment_1824924

    Where does the defrost cycle take place?
    In the air handler in the attic or the compressor outside?

  • Matt_67
    Matt_67 Member Posts: 300

    Defrost is the outdoor coil. Are you sure the compressor isn’t running? The compressor could be running without the outdoor fan going in defrost - I don’t know the sequence on that one without checking.

  • Rob94hawk
    Rob94hawk Member Posts: 20
    https://forum.heatinghelp.com/discussion/comment/1824940#Comment_1824940

    If I happen to catch it happening again I'll go outside and check. It's right underneath my window and I didn't hear it running when the air handler was blasting out cold air.

  • Kaos
    Kaos Member Posts: 365

    If the air handler is blasting cold air than definately defrost. Since the outdoor fan will turn off during defrost, it won't make all that much noise. Usual way this is handled on almost all other inverter heat pumps is to shut off the blower during defrost and don't turn it back on till the coil is back up to temp, I'm surprised it is not an option on these.

    bjohnhy
  • HVACNUT
    HVACNUT Member Posts: 6,470

    The Bosch system will automatically run the fan at high speed whenever the electric resistance heat is energized. Which is either when W is energized as a supplement to the heat pump, or during defrost. If you don't have the electric elements, then you have high speed fan only.

  • worldclasshvac
    worldclasshvac Member Posts: 31

    Your missing the backup heating elements to temper the cold defrost air. Maybe it wasnt wired right and you do have a heat kit. What size breaker is installed for the air handler? Have a pic of the front of it?

  • Rob94hawk
    Rob94hawk Member Posts: 20

    Update: So I was outside next to the unit and I heard the compressor going but no fan. That's apparently the Bosch defrost mode.

    But what I don't understand is why the air handler is blowing cool air at full throttle when in defrost mode.

    Other than this weird mode, it has been able to keep my house a constant 67­­ F and it is 21 F right now.

  • pedmec
    pedmec Member Posts: 1,145

    Where do you think its getting the heat from to defrost the outdoor coil? from your living space. it won't get any heat to get high temp/ high pressure vapor to the outdoor coil if the fan is not moving the air.

    bjohnhy
  • ethicalpaul
    ethicalpaul Member Posts: 7,029

    Be nice everybody!

    NJ Steam Homeowner.
    Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
    See my sight glass boiler videos: https://bit.ly/3sZW1el

  • HVACNUT
    HVACNUT Member Posts: 6,470
    https://forum.heatinghelp.com/discussion/comment/1828519#Comment_1828519

    Read my post from December 5th. It tells you exactly why.

  • Rob94hawk
    Rob94hawk Member Posts: 20
    https://forum.heatinghelp.com/discussion/comment/1828523#Comment_1828523

    It's ok. I have thick skin lol.

    That being said. Read everyone's posts again. Got it.

    Hit 16­°F last night. Worked like a charm (Knocks on wood…)

    Can't wait to see what it can do in 95°F summers.

    Thanks for all the input!

  • ethicalpaul
    ethicalpaul Member Posts: 7,029

    They cool a lot better than they heat, good luck!

    NJ Steam Homeowner.
    Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
    See my sight glass boiler videos: https://bit.ly/3sZW1el

  • Rob94hawk
    Rob94hawk Member Posts: 20
    https://forum.heatinghelp.com/discussion/comment/1828855#Comment_1828855

    Let's see what the electric bill is gonna be compared to my oil bill.

    ethicalpaul
  • Dennis
    Dennis Member Posts: 124

    Definitely in defrost. The cold air blast might be a lack of electric resistance elements. Some of the contractors installing Bosch do not install backup due to the low temperature heating the unit can produce.
    I tend to be aggressive with back up resistance depending on the application. Newer construction that is tight and well insulated might only see 5 kw installed for a 1-3 ton unit. I normally install 10 kw for a 4 ton application while leaving the outside unit switched to 5 ton on the 4 ton blower.

    The Bosch inverter compressor dials in based on the indoor blower speed. The system will work best if the heat pump blower is set the lowest speed it will work with or 350 cfm per ton based on the cooling load for example 4 ton cooling set for 1400 cfm.
    This blast of cold air you're getting might be due to an improper setting of the blower speed. If you don't see any test holes in the ducting, the system was not properly (or at all) commissioned.

    There was an error rendering this rich post.

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,898

    When the unit goes into defrost it shifts to run in air conditioning mode to defrost the outside coil. It will blow cold air into the building no way around that but the air handler should have electric heat strips to counteract the cold AC air.

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