Results 1 to 9 of 9
  1. #1
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212

    Bryant Heat Pump VPS Switch.

    Model Number 650ANX036000ADAA

    Outdoor coil had iced up in heat mode because the outdoor fan
    was off. Outdoor fan is powered through VPS switch. VPS-Vapor
    Pressure Switch. I assume it is a low-pressure switch, and it (definitely)
    is on the (A/C) suction line.

    First question: Is the "suction" (fat) line low-pressure in heat mode?
    I wouldn't think so. The switch kept the outdoor fan off in both
    heating mode and cooling mode. I jumped it out and both modes
    then allowed condenser fan operation. Note that there is a low-pressure
    switch on the liquid line (in A/C parlance).

    Second Question: Why the heck would they do it that way? Why
    wouldn't they run the contactor through the VPS in order to kill
    the compressor?

    I ran the thing in cooling mode and it had (I have a bad memory)
    a 20+ degree temp drop, but ambient was 46 degrees. Inside
    return air was 65.

    I was going to get the heat-mode temp rise but the heat
    strips came on immediately despite a 3 degree temp difference
    between room and setpoint temps. I think it was due to the
    adaptive feature of the thermostat--it knew it needed to
    turn them on. So I have no idea if it heats well, but the
    homeowner seemed to think it was weak without heat strips.
    I was going to disable the heat strips but it was getting late
    and homeowner was cool and suggested we do it in two days
    when he had time off. With heat strips on, temp rise was
    a modest 26 degrees, so I am inclined to believe it is not
    heating well. But how could it cool so well but not heat well?

    I'm going back the day after tomorrow to either charge the thing
    or determine that the VPS swith is indeed nuts. I am hoping
    for 55+ ambient temps so I can (yes?) then rely on the
    nameplate subcooling value to tell me whether the charge
    is low. Today, at 46 F, the subcooling was only 5 degrees
    and nameplate was 14 F, but I wasn't sure where "design
    conditions" really deviated from actual operation.

    ALL of today's calls were heat pumps. It was a bad day.
    Will days ever be all good no matter what I encounter?
    I mean before retirement.

  2. #2
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,634
    Quote Originally Posted by georgelass View Post
    Model Number 650ANX036000ADAA

    Outdoor coil had iced up in heat mode because the outdoor fan
    was off. Outdoor fan is powered through VPS switch. VPS-Vapor
    Pressure Switch. I assume it is a low-pressure switch, and it (definitely)
    is on the (A/C) suction line.
    That is a HEATING Vapor Pressure Switch.

    This outdoor unit is equipped with this heating vapor pressure limiting device which cycles the outdoor fan at high ambient heating conditions.

    The exact ambient which the outdoor fan cycles depends on the indoor unit size, indoor airflow (including restricted filter and/or coil), refrigerant charge and Check-Flo-Rater.

    If this switch cycles at low outdoor ambients, check to ensure an ARI approved indoor/outdoor combination is used, check for proper airflow, and check the refrigerant charge.

    I don't see an email in your profile, so send me an email (address is in my profile), and I will get the service manual off to you.
    Instead of learning the tricks of the trade, learn the trade.

  3. #3
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    I'm a bit slow with heat pumps, so have patience with me here, please.
    If the outdoor temp is HIGH, that would allow the outdoor coil to more
    easily absorb heat without the fan, right? So it is a high vapor pressure
    switch? If outdoor ambient is high, the pressure is high,
    so the outdoor fan turns off?

    Since my case is turning the fan off for cooling
    too, I would have to assume the switch turns off for low pressure.
    That sounds contradictory. That is, I'm confused. Sorry.

    I will send you my email address. Thank you very much.

  4. #4
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,634
    Quote Originally Posted by georgelass View Post
    I'm a bit slow with heat pumps, so have patience with me here, please.
    If the outdoor temp is HIGH, that would allow the outdoor coil to more
    easily absorb heat without the fan, right? Correct So it is a high vapor pressure
    switch? Correct If outdoor ambient is high, the pressure is high,
    so the outdoor fan turns off? Correct

    Since my case is turning the fan off for cooling
    too, I would have to assume the switch turns off for low pressure.
    That sounds contradictory. That is, I'm confused. Sorry. It should not turn the fan off in the Cooling mode.

    I will send you my email address. Check your email.
    *
    Instead of learning the tricks of the trade, learn the trade.

  5. #5
    Join Date
    Aug 2012
    Location
    Palmyra, Missouri, United States
    Posts
    224
    i feel your pain on this same thing. carrier heat pumps used to be wired like this as well. really still to this day dont understand why they are breaking one side of the condensor fan motor high voltage with it. WHY NOT JUST RUN IT IN SERIES WITH 24 V safeties.

  6. #6
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,049
    It's for refrigeration. Not a safety. It's like low ambient for cooling. If pressure drops you don't kill the contactor, you kill the fan to bring up pressure

  7. #7
    Join Date
    Aug 2012
    Location
    Palmyra, Missouri, United States
    Posts
    224

    Frown

    unit i came up to was in heating and was out of refrigerant and the compressor was just rocking and rolling. guess the actual low pressure switch wasnt there.

  8. #8
    Join Date
    Nov 2008
    Location
    Northern California, foothills.
    Posts
    212
    Rundawg's help led me to an informative existing thread on this:
    Again, good job, Rundawg. Good dawg.

    http://hvac-talk.com/vbb/showthread....ressure-switch

  9. #9
    Join Date
    Jul 2007
    Location
    Virginia
    Posts
    5,634
    Quote Originally Posted by georgelass View Post
    Rundawg's help led me to an informative existing thread on this:
    Again, good job, Rundawg. Good dawg.
    Always glad to help out the team.
    Instead of learning the tricks of the trade, learn the trade.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event