Single phase compressor for air-condition

19 Comments / HVAC

Understanding Single-Phase Air-Conditioning Compressor Motors

The compressor is the heart of an air-conditioning or refrigeration system, responsible for circulating refrigerant throughout the system. Similar to the human heart pumping blood, a compressor failure can paralyze the entire system. In single-phase air-conditioning systems, compressors are typically powered by single-phase electric motors, commonly running capacitor motors. Popular compressor brands include Copeland, Daikin, Toshiba, and Mitsubishi.

This post will explain the basic concept of single-phase compressor motors, how to check their wiring and winding condition, and best practices for troubleshooting.

Wiring for Single-Phase Motors

Single-phase motors in air-conditioning systems use different capacitor setups to start and run the motor. The two common wiring configurations are:

  1. Run Capacitor:
    • Supports continuous operation of the motor.
    • Maintains motor efficiency during operation.

  1. Start and Run Capacitor:
    • A start capacitor provides the necessary torque to initiate motor rotation.
    • A run capacitor ensures smooth and efficient operation after the motor starts.

Identifying Compressor Motor Connections

Single-phase compressor motors typically have three connections on the winding:

  • Common (C)
  • Starting (S)
  • Running (R)

To determine these connections, follow these steps:

Using a Multimeter to Measure Resistance

  1. Measure resistance between all three connections:
    • Example:
      • Point 1 to Point 2 = 3 ohms
      • Point 2 to Point 3 = 8 ohms
      • Point 3 to Point 1 = 6 ohms
  2. Draw a triangle and label each side with the measured resistance values.
  3. Determine the connections using the following rules:
    • Common (C): Highest resistance value (e.g., 8 ohms).
    • Starting (S): Second-highest resistance value (e.g., 6 ohms).
    • Running (R): Lowest resistance value (e.g., 3 ohms).

Checking Compressor Motor Winding Condition

To assess the motor’s winding condition, there are two primary checks:

1. Winding-to-Winding Short

  • Method:
    1. Set the multimeter to ohms mode.
    2. Measure resistance between all three connections and the compressor body (earthing).
  • Results:
    • Good Winding: Resistance is infinite (no continuity to earth).
    • Shorted Winding: Resistance is 0 (continuity exists to earth).

2. Partially Shorted Winding

  • Method:
    1. Measure resistance between:
      • Common (C) and Running (R).
      • Common (C) and Starting (S).
    2. Record the values.
  • Formula to Evaluate Winding Condition:
    The resistance of the starting winding should be 3 to 6 times higher than the running winding.

Tips for Diagnosing Compressor Motor Issues

  1. Understand Resistance Ranges:
    Familiarize yourself with standard resistance ranges for your specific compressor model.
  2. Inspect Capacitors:
    Faulty start or run capacitors can cause motor failure. Always check capacitors during diagnostics.
  3. Check for Physical Damage:
    Inspect the compressor for visible damage, such as burnt terminals or overheated windings.
  4. Test in Isolation:
    If possible, isolate the compressor from the circuit to eliminate external factors during testing.
  5. Regular Maintenance:
    Clean and inspect connections regularly to prevent faults caused by corrosion or loose terminals.

Key Takeaways

  • Single-phase compressor motors are integral to air-conditioning systems, and their proper function ensures overall system reliability.
  • Understanding motor connections (C, S, R) and winding conditions is essential for troubleshooting.
  • Using simple tools like a multimeter, you can diagnose common issues like short circuits and partially shorted windings.
  • Always ensure resistance values fall within the acceptable range (starting winding resistance = 3–6 times running winding resistance).

By following these guidelines, you can maintain and troubleshoot single-phase compressor motors effectively, minimizing downtime and maximizing system performance. For further assistance, always consult a certified HVAC technician or refer to the manufacturer’s documentation.

Share The Post :

Related Posts

19 thoughts on “Single phase compressor for air-condition”

  1. Frank

    air conditioner soft starter series including:
    1. Single-phase air-conditioner soft starter
    TL-ASSU220P3 applies to single-phase 1P/2P/3P air conditioner. It is used either for 50HZ or 60HZ.
    TL-ASSU220P5 applies to single-phase 4P/5P air conditioner. It is used either for 50HZ or 60HZ.
    TL-ASSU220P7 applies to single-phase 6P/7P air conditioner. It is used either for 50HZ or 60HZ.
    2. Three-phases air-conditioner soft starter
    TL-ASSU380 applies to those three-phases air-conditioner soft starter and electric motors which the power is less than 18.5KW. It is used either for 50HZ or 60HZ.

    The air-conditioning soft starter is an embedded air-conditioning controller, it regulates the start-up voltage and current of the compressor intelligently by utilizing advanced micro-control technology of SCM, and effectively reduces the instantaneous current and power of the compressor while starting-up, thus protects the compressor and prolongs its life. Simultaneously, it also depresses the shock while air-conditioning starting up in the power supply network.

    The soft starter is applied with embedded system technology. It has many advantages such as smaller size, lighter weight, an anti shock, longer life, higher level in reliability and stability, easier installation etc. Especially, it functions well in some harsh condition.

    The most important feature of our product is it can control the highest launching transient current of air conditioner to be about 2 times as great as its rated current,never exceed 3 times. It can effectively protect air conditioner compressor, extend its service time. Additionally, when it detects the compressor couldn’t start because of the imbalance of pressure,it will protect the compressor, then restart after 90 seconds.So then effectively prevents the compressor from overburning for failure start.

  3. kennard

    If the sum of C to R (ohm)and C to S (ohm) is equal to S to R (ohm), then the compressor is good.

  4. regs

    commmon terminal can be taken from highest reading of resistance.ex.;term.1-2=18 ohms,2-3=12 ohms and 1-3=6 ohms
    take the highest reading as the base.term 1-2=18 ohms.terminal that is not indicated is the common terminal w/c means terminal 3 is the common. Then look for the second hignest and get the other terminal as the start and lastly the lowest is the run.
    c=3
    s=2
    r=1

  6. ahmed

    hi sir
    i didnt understand what you mean by
    The formula to determine a winding condition is good,the resistance of starting winding is equal 3 to 6 times of running winding
    could you pleas explain than
    many thanks

  7. John

    I have an American Standard heat pump . Once a week the unit will trip the circuit breaker . Single phase . The start capacitor and run capacitor are good as well as the rest of the controls . the breaker is new and properly sized and the connections are tight . The wire size is also correct and when the unit is running the amperage is well within specs . Can the compressor have a dead spot in the windings that will cause this ? I dont know what else to look for . Can you help ?

  8. tcfkat

    @kennard: partial winding shorts cannot be detected by a DC resistance measurement. The sums will always be correct, regardless if part of a winding is shorted. What only gives a correct answer is an AC measurement.

    @John: maybe there is sometimes a short power outage, which stops the compressor. Because of the differential pressure present in the system immediately after a stopped engine the motor is unable to restart, causing the breaker to trip. Normally there is a so called Klixon (selfresetting thermal circuit breaker) to catch such cases. Or the compressor is started, run and restarted by a defective control circuit.

    PS pardon my bad english

  9. tunde bello

    my chestfreezer is working but shocks when the scratched area is touched.whats the cause and solution.

  11. [4]

    Since the admin of this website is working, no uncertainty very
    rapidly it will be renowned, due to its feature contents.

  15. John Harmsworth

    For a single phase unit that trips a breaker once a week, the probable cause is the unit short-cycling. This occurs when the unit satisfies the heating or cooling requirement and shuts off, then comes back on shortly afterward and before the discharge pressure has had a chance to equalize with the low side pressure. Some tims this occurs when the homeowner turns the stat up or down slightly shortly after the unit has shut down. Some units may require an anti-short cycle timer to reduce this occurence. If the unit works alright the rest of the time, it is highly unlikely there is anything wrong with the compressor

  16. Peter

    please kindly explain to me which component parts do I have to examine in other to solve problem of instantaneous power failure after installed a new compressor and it won’t start up to enable me charging it with refrigerant to it’s full load capacity. Unit make is Daikin air conditioner

  17. Bleu Red

    I have compressor actual pin .

    O 7 ohms O

    8 ohms 12 ohms
    O

    How to find common ?
    Not inverse traingle …pin configuration.

  18. Bleu Red

    I have compressor actual pin .

    O 7 ohms O

    8 ohms 12 ohms
    O

    How to find common ?
    Not inverse traingle …pin configuration.

Leave a Comment