Heat the bulb by using a halide torch or similar device and observe the valve stem movement.

Remove the power head from the unit, heat the bulb with a torch while using a scale to measure the distance the diaphragm has moved.

Chill the bulb in ice water while observing the compressor for an increase in suction pressure.

Place the sensing bulb in ice water and then warm by hand. Observe flood-through and temperature change at the suction line.