Trial
Attach (+) power supply to pin±3, ground pin±2 and connect a test light between pins±1 and±3.
Note: Use a 12V, 3-18W light bulb. Immerse the A/C thermostat in a glass of ice water and check the control light.
The light bulb should go out at a temperature of 2-4°C or lower and should come on at 4-5°C or higher. If the light bulb does not behave as installed» replace the A/C thermostat.