Results 1 to 9 of 9
  1. #1

    Troubleshooting help with a single-phase 5Hp motor/compressor

    Good evening and Happy New Year to all.

    I am trying to find the cause for the overheating of a 5 HP single phase motor which turns a belt driven refrigeration compressor. The FLA at the plate reads 21.5 amps, while the running amps in my meter never read above 21.0 amps.
    The motor does not run continuously: it has a thermostat controlled pumpdown type control system, cycled by the low pressure control. Nevertheless, as the motor runs for a few hours, it becomes hotter and hotter until the thermal protector opens. I already replaced both the start and run capacitors. One thing I did notice is that this is a 230 volts motor, not the regular 208/230 volts, but the line voltage stays between 208 and 210 volts. It had been working without trouble for 5 years. Never re-wound before. What do you thing?

  2. #2
    Join Date
    Jun 2003
    Location
    Chicago, IL
    Posts
    4,426
    is the condenser clean and the fans working properly?

  3. #3
    Join Date
    Dec 2009
    Location
    Montreal,Québec, Canada
    Posts
    9
    Is it possible that the motor is cycling a lot in an hour? A leaking solenoid might cause an over cycling of the motor who eventually will be hot.

    It could be a cycling cause from a High to low valve of the compressor.

  4. #4
    Join Date
    Feb 2010
    Location
    Ontario Canada
    Posts
    1,341
    Is the motor 3 phase? Check for same voltage on each line.
    Never give up; Never surrender!

  5. #5
    Join Date
    Apr 2004
    Location
    NJ
    Posts
    155
    Have you checked the belt tension and/or pulley adjustment?

    Also, if it is an air over motor, is it located in an area where the is poor air circulation?

  6. #6
    Join Date
    Dec 2009
    Location
    Montreal,Québec, Canada
    Posts
    9
    I don't think that 3 phases motor requires capacitors for run and start. So it must be single phase motor.

  7. #7
    Join Date
    Oct 2011
    Location
    south al.
    Posts
    111
    Sounds like possible motor problem, if it is drawing .5 amps below full load amps at 210v then at 230v it would be over amping. The average running amps should never be that close to fla or it will over heat. What about bearings or belt tentionas jaypslugger mentioned?

  8. #8
    Grease bearings.
    Loosen up the tension on the belt.
    If this fails then you only have 2 things left.
    Esther te compressor is starting to get tired or you need a new motor

  9. #9
    Join Date
    Sep 2009
    Location
    Stumptown,USA
    Posts
    1,251
    Every time that motor overheats and opens the thermal protector the insulation on the run windings becomes a little more degraded. If you didn't need a new motor when this all started you do now. Chances are a partial short circuit in the middle of the run winding started the overheating condition, which is now getting worse. Single phase is not as torqey as 3 phase, but you got what you got! Try to get a 208/230 motor next time. I agree with JJ could also be the compressor getting tired.
    Challenge yourself, take the CM test --- Certificate Member since 2004 ---Join RSES ---the HVAC/R training authority ---www.rses.org

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