How do I test a mechanical fridge thermostat using a multimeter?

Testing a mechanical (capillary tube) refrigerator thermostat determines whether its electrical contacts are opening and closing properly in response to temperature changes.

Tools Needed & Setup

• Multimeter (set to Continuity →111) or lowest Resistance / Ohms Ω)
• Screwdriver & needle-nose pliers
• Bowl of ice water (or a cup of ice with a small amount of water)

Step-by-Step Testing Procedure

1. Safety First: Unplug the refrigerator from the wall outlet before removing any panels.
2. Locate & Access: Remove the thermostat housing inside the fridge compartment (usually behind the control dial light box assembly).
3. Disconnect Wires: Take a picture of the wire connections for reference, then use pliers to gently pull the spade connectors off the thermostat terminals.
4. Remove the Assembly: Carefully pull out the thermostat and its thin metal capillary tube (be careful not to kink or snap the capillary tube).

1. Room Temperature Test (Closed Contact Check)

At normal room temperature (around 20∘C/68∘F or warmer), the gas inside the capillary tube expands, pushing the internal contacts together.

• Turn the thermostat dial to its coldest setting (highest number, e.g., setting 5 or 7).
• Touch the multimeter leads to the main terminal pins (usually labeled 3 and 4, or the two main electrical terminals).
• Expected Result:
  • Continuity / Low Resistance (0 to 1 Ω): The thermostat is closing the circuit properly to call for cooling.
  • No Continuity / Infinite Resistance (O.L): The contacts are stuck open, meaning the compressor will never turn on. The thermostat is defective.
• Now, turn the dial to the “OFF” or “0” position (if equipped).
• Expected Result: The multimeter should immediately show O.L (Open Loop / No Continuity).

2. Cold Water / Ice Test (Open Contact Check)

This test confirms whether the bellows contract and cut off power when reaching target temperatures.

1

Submerge Capillary Probe

Place the tip and lower portion of the capillary coiled wire into a bowl of ice water for 3 to 5 minutes. Keep the main terminal body dry.

2

Set Dial to Lowest Cold Setting

Turn the control dial to setting 1 (least cold setting).

3

Measure Terminal Resistance

Touch the multimeter probes to the same two terminal pins.

4

Check for Circuit Break

Expected Result: The meter should read O.L (Open Circuit) as the gas contracts and opens the contacts to stop cooling.

Diagnostic Summary