How to Test Refrigerator Compressor Windings Using a Multimeter?

Testing refrigerator compressor windings is one of the most reliable ways to determine if a compressor’s electric motor has suffered an internal failure (such as an open circuit, shorted turns, or a ground fault).

If your compressor is clicking, humming without starting, or tripping your home’s circuit breaker, perform these checks before condemning the unit.

Safety First & Preparation

1. Unplug the Refrigerator: Completely disconnect power from the wall outlet.
2. Access the Compressor: Remove the rear lower access panel of the refrigerator.
3. Remove Starting Components: Pull off the protective plastic cover, disconnect the wires, and unplug the PTC start relay and overload protector directly from the 3 terminal pins on the compressor.
4. Inspect the Pins: Ensure the 3 copper or brass pins are clean and free of corrosion or burnt residue.

Understanding the 3 Terminal Pins

The compressor motor contains two internal wire coils: the Start Winding (used to kick-start the rotor) and the Run Winding (used during continuous operation). These two coils share a common connection point inside the housing, giving you three exposed terminal pins arranged in a triangle:

• C: Common
• S: Start
• R: Run

       [ C ] (Common)
        /   \
       /     \
  [ S ]-------[ R ]
 (Start)     (Run)

Step-by-Step Multimeter Testing Procedure

Set your digital multimeter to measure Resistance in Ohms (Ω) (or set it to the lowest range, e.g., 200Ω).

       [ STEP 1 ]               [ STEP 2 ]               [ STEP 3 ]
   Check Continuity         Measure Individual        Test Ground Fault
      (Open Loop)               Resistances             (Pin to Frame)
  ──────────────────       ──────────────────       ──────────────────
   Measure all 3 pairs      S-to-C + R-to-C          Probe each pin to
   (C-S, C-R, S-R).         MUST EQUAL S-to-R.       bare metal casing.
   Any "OL" = Dead          Formula: $R_{SC} +       Must show "OL". Any
   compressor.              R_{RC} = R_{SR}$         reading = Shorted.

Test 1: Check Winding Continuity (Open Circuit Test)

Measure resistance across all three pin combinations:

1. Common (C) to Start (S)
2. Common (C) to Run (R)
3. Start (S) to Run (R)

• Expected Result: You should get a low resistance reading (typically between 2Ω and 30Ω) on all three measurements.
• Failure Condition: If any pair displays “OL” (Open Loop / Infinite Resistance), an internal winding has burnt out and broken continuity. The compressor is dead and must be replaced.

Test 2: Verify Winding Resistance Values (The Addition Rule)

In a healthy single-phase induction compressor motor, the electrical relationship between the windings strictly follows this rule:

Resistance (Start to Run)=Resistance (Common to Start)+Resistance (Common to Run)

• Start Winding (RSC​): Higher resistance (thinner wire, more turns). Typically 5Ω to 20Ω.
• Run Winding (RRC​): Lower resistance (thicker wire, fewer turns). Typically 2Ω to 10Ω.
• Total Across Both (RSR​): Highest resistance (sum of both windings).

Example Reading:

• C to S=12Ω
• C to R=4Ω
• S to R=16Ω (12+4=16)
• Failure Condition: If RSR​ does not approximately equal RSC​+RRC​, or if two pins show an abnormally low reading (e.g., 0.2Ω), there is an internal short circuit between the winding turns.

Test 3: Ground Fault Test (Short to Ground)

Even if the windings read correct resistance, an internal wire may have melted or broken, touching the metal compressor shell.

1. Switch your multimeter to Continuity Mode (Beep) or high Ohms (MΩ).
2. Scrape away paint or rust on a bare copper pipe or the bare metal housing of the compressor to ensure a clean ground connection.
3. Place one probe firmly on the bare metal ground point.
4. Touch the second probe to Pin C, then Pin S, and finally Pin R.

• Expected Result: The meter must show “OL” (Infinite Resistance) for all three pins, and no beep should sound.
• Failure Condition: If the meter beeps, shows zero resistance, or gives a specific resistance reading to ground on any pin, the compressor is shorted to ground (shorted to frame). This will trip your breaker or blow a fuse instantly.

Quick Diagnostic Result Matrix