Heat pump compressor not running

Discussion in 'HVAC Heating & Cooling' started by jfryc, Feb 20, 2011.

  1. jfryc

    jfryc New Member

    Messages:
    1
    Location:
    NJ
    I have a 15 year old FHP geothermal heat pump, the compressor won't start. In heat mode there is a slight humming, and every 30 seconds or so louder buzzing noise for a few seconds. The compressor is getting 220V to the contacts, the resistance between the then is in the range of 3 to 7 amps. I tested the start capacitor with a simple DMM using a resistance and volt modes, seems to work as it should. Any ideas? Time for a new heat pump? Should I try a new start capacitor anyway?
  2. gator37

    gator37 Retired prof. engr.

    Messages:
    108
    Location:
    Alabama
    Through disconnect switch shutting off power to the condenser unit. Test the compressor for open circuit and short wih ohm meter (ohms resistance not amps). Disconnects power leads on the compressor. Test acrossed the leads should get some reading verifying continuity (no reading results of an open circuit) and then test each lead to the compressor housing, should not get a reading, if so compressor is shorted to ground. It has been 40 years and that is about all I remember.
  3. david_griffin

    david_griffin New Member

    Messages:
    25
    Location:
    Denver, CO
    You are not able to test start capacitor without the heavy load. It can look good on the table when you use multimeter but it will not work in the real circuit. Buzzzzzzing means likely a capacitor. If you had shorts then this device would blow fuses.
  4. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,271
    Location:
    Maine
    How do you test in "in circuit"? As far as I know the only way to test a capacitor is to charge it up, disconnect it and put the meter across the terminals. You either need an analog meter ( old needle style ) or a fairly expensive multi with a capacitor test function.
  5. david_griffin

    david_griffin New Member

    Messages:
    25
    Location:
    Denver, CO
    It is capacitor for AC circuit. Its role is to shift phase and conduct big current to the second coil. You will not measure it wit small voltage multimeter or by charging it wit DC and then discharging. You need Ampers not miliampers to test it.
  6. Tom Sawyer

    Tom Sawyer In the Trades

    Messages:
    3,271
    Location:
    Maine
    Who said anything about charging it with DC?
  7. david_griffin

    david_griffin New Member

    Messages:
    25
    Location:
    Denver, CO
    I would like to know the answer what caused the malfunction ?
    It would be interesting.
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