Gain access to the point where the power cord connects to the refrigerator. If the conductors are bundled with other wires, separate one conductor wire and keep it isolated. Currents flowing though wires running in close proximity to the one under test may influence your readings.
Set a clamp-on ammeter to "auto-range" or to the appropriate current range if auto-range is not available. Open the clamp jaws by depressing the "Open" button. Place one conductor from the refrigerator cord between the jaws and close them gently, positioning the conductor in the center of the jaws.
Observe the display on the meter. It may take a few seconds to register a reading. With the compressor switched off, the reading will be very low. Wait until the compressor turns on, and observe the new reading. Subtract the original reading from the second reading to find the current drawn by the compressor.