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  1. #1
    Join Date
    Apr 2011
    Location
    Florida
    Posts
    103

    amp spike on carrier 5 ton heat pump

    so i installed 2 carrier 5 ton heat pump systems in a doctors office about a week ago. customer called today and said this is the first time the used to the heat and they tripped the main 200 amp breaker. checked both units and they are pulling normal amperage. the main feed coming into the panel box with both unit's off was 49 amps. both unit's running with back up strips engage about 110 amps total on main feed. thats everything running in the building. so way are my units tripping the breaker? well on further diagnostics i found the unit's pulling a quick 159 amps on start up. so my question is why would these bad boys pull that much on start up. i checked caps, i checked voltage drop on start up and i checked pressures on start up. everything looked fine. so i'm stumped any ideas to fix the problem would be appreciated.
    Aire Force A/C and heating
    Florida
    since 1988

  2. #2
    Join Date
    Jun 2004
    Location
    St Paul, minnesota
    Posts
    1,208
    Install hard start caps

  3. #3
    Join Date
    Dec 2011
    Location
    Northwest Georgia
    Posts
    111
    Agreed get hard start caps in both units, use a bigger one like a TO5 or even better trane hard start cap and potential relay

  4. #4
    Join Date
    Nov 2011
    Location
    USA
    Posts
    384
    I'm not an electrician, but I think I'd suspect the electrical service. Heat pumps don't generally trip mains. Did you by chance check for a voltage drop on start-up? Is the main "running hot"?

  5. #5
    Join Date
    Feb 2012
    Location
    Alabama
    Posts
    378
    Quote Originally Posted by Saturatedpsi View Post
    I'm not an electrician, but I think I'd suspect the electrical service. Heat pumps don't generally trip mains. Did you by chance check for a voltage drop on start-up? Is the main "running hot"?
    Agreed. I would check the panel. Take the main br out and see what the "ears" look like on the panel. Start kit is always good, but I bet the problem isn't with the units. Let us know.

  6. #6
    Join Date
    Nov 2007
    Location
    Sherman, TX
    Posts
    9,441
    Agree with checking the panel connections.

    And, you might consider a delay on make timer on one of the heat pumps, to stage start up......same as we do with sequencers on electric furnaces.

    Also.....how much element heat do you have? Did you check the current draw with ALL of the elements running? Two five-ton heat pumps would likely have a total of 40kw strip heat on them around this area. That would run 160+ amps itself.
    Technical incompetence is NOT a sales tool....

  7. #7
    Join Date
    Feb 2012
    Location
    Alabama
    Posts
    378
    Spot on with the strip heat check. I would want to be sure these are on.

  8. #8
    Join Date
    Aug 2006
    Posts
    2,599
    Are they on Setback thermostats? We have four Carrier HP/RTUs, on cold mornings the thermostats were slamming on the compressor, and all three stages of heat, on at once. We went with thermostats with Y1 for the compressor and 3 stages of electric heat with smart recovery. The units wiring diagrams shows 1st stage with one strip of heat, 2nd stage with two strips of heat. So we had to move some wires around.

    BTW, Drs. Offices are notorious for overloading panels. They have medical equipment techs. coming in and install the latest and greatest medical gizmo. Pop a new breaker in, test and go. Then we get called in for more cooling/heating to cover this area, and bam there are problems.

  9. #9
    Join Date
    Jan 2012
    Location
    Russell Springs Ky
    Posts
    49
    I wouldn't be afraid to pop in a new breaker. A weak breaker has given me headaches more then once.

  10. #10
    Join Date
    Feb 2012
    Location
    Alabama
    Posts
    378
    Quote Originally Posted by BoatMechanicMatt View Post
    I wouldn't be afraid to pop in a new breaker. A weak breaker has given me headaches more then once.
    Actually had an electrician (experienced with own biz) tell me there was no such thing as a weak breaker!

  11. #11
    Join Date
    Feb 2012
    Location
    Dayton,OH
    Posts
    7
    +3 on the electrical. I would check the main breaker amperage without the heat pumps operating, then bring on strips, and start the heat pumps. I bet there is an issue with main.

  12. #12
    Join Date
    Apr 2011
    Location
    Florida
    Posts
    103
    check voltage on start up. had 244volts didn't drop any on start up. got 5kw heat in each pulling 20 amps per unit. but this jump is only on start up at the condensing unit. and only one is doing it. the other one jumps to 85amp on start up which is normal from my experience. i put hard starts on both units as a band aid and now i'm getting a jump to 35 amps on startup. the only thing i can think of is the one pulling high amps has about 70 foot of line set to the handler in the attic. which is not my choice by no means. but all my electrical is tight and good voltage. main breaker is good i already took it out and checked it that was the first thing i did when i got there. thanks guys for the input.
    Aire Force A/C and heating
    Florida
    since 1988

  13. #13
    Join Date
    Apr 2011
    Location
    Florida
    Posts
    103
    Quote Originally Posted by madhat View Post
    Are they on Setback thermostats? We have four Carrier HP/RTUs, on cold mornings the thermostats were slamming on the compressor, and all three stages of heat, on at once. We went with thermostats with Y1 for the compressor and 3 stages of electric heat with smart recovery. The units wiring diagrams shows 1st stage with one strip of heat, 2nd stage with two strips of heat. So we had to move some wires around.

    BTW, Drs. Offices are notorious for overloading panels. They have medical equipment techs. coming in and install the latest and greatest medical gizmo. Pop a new breaker in, test and go. Then we get called in for more cooling/heating to cover this area, and bam there are problems.
    YEP! see it all the time.
    Aire Force A/C and heating
    Florida
    since 1988

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