Current draw during startup - Carrier AC
Page 1 of 3 123 LastLast
Results 1 to 13 of 33
  1. #1
    Join Date
    Jun 2005
    Posts
    28
    I have a Carrier Infinity Weathermaker 58MVP furnace and air conditioner. Newer AC with Puron technology that I believe is 3.5 ton unit. I live off-grid and last year ran the AC no problem with my 10KW military surplus diesel generator. I changed generators to a 12.5KW diesel model with an Isuzu diesel engine. I tried starting my AC and the blower motor came on and then when the compressor goes to start it just stops. It does not really seem to overly bog the generator. I am wondering if I have a problem with the AC compressor or if it is not getting enough power from the generator. I was outside and saw the fan on the outdoor unit start to spin and then boom it just quits. I would like to know what the current draw during motor start is?? I read in the manual that it is 30 or 32 amps (can't remember which) for locked rotor rating. Is that the max it draws during motor start-up or is it higher than the locked rotor rating?? Could it be that the power source is fine and there is something else at play here? Is there a way of using motor start capacitor to ease the starting?

  2. #2
    Join Date
    Nov 2003
    Posts
    125
    Has anyone checked the voltage and amp draw out at the condenser? Since you changed generators?

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,273
    First of all, if you're generating your own power, I would think you'd have at least some idea of the quality of power you're receiving from the generator. Look at the nameplate on the outside of the condenser. It should state the minimum and maximum voltage ranges the unit can safely operate at. The generator should put out enough volts and watts to be able to satisfy this range.

    Eliminating a supply voltage problem, if I saw a condenser fan begin to turn and then stop, my reaction would be based on:

    a) did it slowly try to spin up and never come to full speed before cutting out? If so, may be fan motor and/or run cap.

    b) does it spin, then lock up, spin then lock up? Bad bearings on fan motor.

    If the condenser fan motor runs erratically, it will sooner or later cause the compressor to kick out on internal protector (overload).

    Your best bet, of course, is to get a tech out there who's encountered this problem (except perhaps for homeowner generated electricity) a million times and can make the fix in his sleep.

    Just curious...do you really save much money making your own power vs. what the grid would charge to give you power 24/7? Maybe you're out in the sticks and it's just cheaper to make your own juice than to pay for the power co. to run and hook up power to your house.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  4. #4
    Join Date
    Jun 2005
    Posts
    28
    Shophound,

    Thanks for the replies. I am too far from lines to get them run to my house. I am in the process of putting in a solar electric system which will consist of 4200 watts of solar power. A 40,000 watt hour battery bank and inverters. The generator is a top of the line Isuzu diesel engine coupled with a Marathon generator head. This is not a gasoline powered portable type generator. It is a permanently mounted unit. Marathon and Isuzu are two well respected pieces of equipment. To try to describe the problem a little better. I called for cooling by turning the thermostat to cool position. I believe there is a short time delay programmed into the Carrier. The blower motor in the indoor unit came on and then when the compressor went to start it shut down within a matter of a split second. I have run the compressor off of both 240 single phase and 208 single phase and it ran fine off of both. It is now being attempted to be run off of 240 single phase. I am still really interested in the question of current draw during motor surge when starting and if that is given by the locked rotor rating?

    Mike

  5. #5
    Join Date
    Jun 2005
    Posts
    28
    Shophound,

    The old military generator unit had a watt meter on it and with AC running and normal household loads such as TV, washing machine etc the most it ever drew was in the 3500 watt range. Of course higher during the motor starting surge of the compressor. The new generator is rated at 12,500 watts. If the compressor were to draw 30 amps at 240 volts (I use this number assuming that the locked rotor rating is the maximum current the motor will draw and please correct me if this is wrong) that would be 7,200 watts.

    Mike

  6. #6
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    The 30 or 32 amp figure is probably maximum fuse size and/or minimum circuit ampacity. I just looked at the data plate for a 3 ton 10 SEER Trane air conditioner. Its locked rotor amps was 87. Yours will be in that ballpark. The LRA should be printed on the AC's data plate.

  7. #7
    Join Date
    Nov 2003
    Posts
    125
    Has anyone checked the voltage and amp draw out at the condenser?

    Or are you feeding it 110 volts thru a bad breaker?

  8. #8
    Join Date
    Jun 2005
    Posts
    28
    Irascible,

    I got the locked rotor amps from the Carrier manual and will go back and check. Should there be a data plate on the outside unit? Does the unit actually pull its locked rating during start-up?

    Mike

  9. #9
    Join Date
    Jun 2005
    Posts
    28
    bbk,

    Good question and no I haven't checked for a bad breaker or called out my service tech yet. With our heat wave starting this weekend he is probable up to his ears in service calls right now. You are thinking that perhaps only one side of the breaker is feeding power to the compressor? It is a double breaker in the breaker box to get the 240 of course. In addition we have the fuses out near the outsoor unit. Is it possible we have burned out one fuse and it is only getting 110 volts because of that? The 30 amp breaker in the house is not tripping when the unit tries to start.

    Mike

  10. #10
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    Originally posted by mikecales
    Does the unit actually pull its locked rating during start-up?
    Pretty much. But it's literally (usually) a fraction of a second.

    You should find out if your compressor has a hard start kit on it. It could be OEM or an aftermarket product like KickStart. Either one can potentially reduce the duration of the spike in amp draw. I've had customers who had dimming lights and buzzing circuit breakers when their compressors started. The KickStart alleviated those symptoms. Make sure it's sized right.

  11. #11
    Join Date
    Nov 2003
    Posts
    125
    Is it possible we have burned out one fuse and it is only getting 110 volts because of that?
    ================================================== ===========

    WAAAAY!

  12. #12
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,633
    Where would the 110 volts be going once it left the unit? The only answer to that quesion that I'm aware of is a really bad one.

  13. #13
    Join Date
    Jun 2005
    Posts
    28
    Irascible,

    Thank you kindly for the reply. Would my installer know if it had a kick start type of unit on it? I don't think at the point of purchase and installation that anything was added extra so if it is there it would have to be a factory type of unit. Who installs the kick start type of unit the HVAC contractor or an electrical contractor?

    Mike

Page 1 of 3 123 LastLast

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