Blog About Stuff That's In Your Home | Appliances and Stuff

20 Jul 10 HVAC Ohming Compressor Windings

I show how to ohm compressor windings to see if the compressor checks out electrically.

Tags: Compressor, HVAC, Ohming, Windings

Reader's Comments

  1. |

    @robertcyders I’m not sure. You could test the scroll compressor in the same manner as long as it’s single phase. Three phase compressor should ohm the same between each winding.

  2. |

    @2170509 The valve could have got stuck if a piece of trash clogged the orifice. Sometimes, an oil flood back can simulate a stuck valve. By the way, I prefer Sporlan expansion valves. Enough said.

  3. |

    Look at 1:47 in the video. You have your HS33 Fieldpiece meter set on continuity. You have a tone, a light, and the knob is pointing to this setting. I have the same meter. What should you be reading on ohms on a scroll compressor let’s say 4 tons?

  4. |

    I have installed Petra chiller its expansion valve got stuck 05 to 06 times in two years there is installed Danfoss SS body valve, Please reply what cause of getting stuck the expansion valve.
    M. Ismail

  5. |

    @juanater2000 It should be running until the indoor temperature reaches the thermostat set point. Your system could be shutting off on high head pressure. Try cleaning the condensing coil.

  6. |

    @deyenak1 I’ve never known that to happen. I have had a compressor blow out after energising it with power.

  7. |

    @2170509 You should just weigh in the refrigerant charge. Don’t be too concerned with the suction pressure unless it’s too low and the line is icing up.

  8. |

    I have installed 1/2 hp compressor Danfoss 134 a in fridge its getting to heated and compressor return came means suction line temp. came at above 20 psi I read in book at 80 Fahrenheit, suction allowable temp 30 to 20 Psi so 20 psi pressure of suction line is it suitable? Please Reply Dr. Zarkloff

  9. |

    were those compressors under pressure because my teacher say’s that checking ohms at the terminals on the compressor might blow out on you. What can you tell me about that

  10. |

    me again house is 1700sq ft 4 ton unit

  11. |

    me agail house is 1700sq ft 4ton carrier unit

  12. |

    Hi i was adjusting my swing setting and wondering my unit runs about 14min on and 14 min off . 100f out side. i know theres alot more to factor in but what do you think about that? would it be more efficent to run on say 10 min ? how long should it run at that outside temp aproxx? thanks

  13. |

    Resistance measurement cannot determine a shorted coil. I mean any type of coil specially the ones in a compressor. Although it can determine an open winding which rarely happens. A ring test can be performed using an oscilloscope and a signal. Even then it is not 100% reliable. I don’t even know why some technical books have sections in measuring Resistance in coils. It is useless and a waste of time and may lead to confusion.

  14. |

    Hi, Please make me know, can we charge the gas in the system with gas? when we know TR of the system I am talking about gas quantity in weight I know when the system RFT increase gas quantity also increase but is there available thumb rule when capacity so and so then quantity so and so.

  15. |

    An open in the winding will help you with DC resistance measurement, but if there was a short you would not be able to measure it with a regular ohmeter.

  16. |

    When you use an ohmmeter you are only measuring the DC resistance of the compressor coil which are very low. Remember the winding act upon the 60HZ cycle of the house current!! You have to measure IMPEDANCE which is not the same as resistance!! You have to know the size of the wire the number of turns, the size of the loop and what the core is made of then the frequency of the current which is 60 HZ. Measuring DC resistance on compressors are useless. Now coils that has many turns its ok.

  17. |

    You are only measuring the DC resistance of the coil. I would use what you call a ring test. It is the same way we determine a bad flyback transformer in a television. Note that coils characteristic are measure in IMPEDANCE not in RESISTANCE which is what your meter is reading. Coils IMPEDE current they do not resist them. I think AC technician do not understand enough about electricity. Even the ones in the field for a long time.

  18. |

    @2170509 It sounds like the compressor is shutting down on a high head pressure. Have you cleaned the condensing coil?

  19. |

    @2170509 Not to step on the doc, but might I suggest you have a restriction in your line. Possibly at your TXV. It would make sense if your compressor were not getting enough refrigerant intermittently. It would shut down, cool off then restart. If I were you I would try and blow out the lines with nitrogen.

  20. |

    It’s working but condition is that when compressor cools it starts smoothly but when compressor have been runing for long time electricity goes out when electricity comes back after dealy the time it does statr because it gets hot. after delaying 05 to 10 minutes it starts.

  21. |

    It’s working but condition is that when compressor cools it starts smoothly but when compressor have been runing for long time electricity goes out when electricity comes back after dealy the time it does statr because it gets hot. after delaying 05 to 10 minutes it starts.

  22. |

    @2170509 Mathematically, the windings checked out good. Does it run okay?

  23. |

    Sir, I have installed the compressor which gets so I checked the compressor so it’s C-S = 0.024 Ohms , C-R = 0.005 & S-R = 0.029
    I found that compressor is electrically O.K as per your teaching but make me know that C-S ohms is too high as compare to C-R. Is this reading is sufficient?

  24. |

    @extreme383 I can’t say for sure. It just doesn’t seem logical that the evaporator ices up and your pressures are the same on and off.

  25. |

    When the refrigerant piping RFT increase so should the OD increase? or if the OD is increased on which side does the OD increase.
    M. Ismail