The correct answer is D) Place the sensing bulb in ice water and then warm by hand. Observe flood-through and temperature change at the suction line. This is the correct method for testing a thermostatic expansion valve because it simulates the actual operating conditions of the valve. By chilling the bulb in ice water, you can observe the valve's response to a decrease in temperature, and then warming the bulb by hand allows you to see how the valve reacts to an increase in temperature. Monitoring the flood-through and temperature change at the suction line provides a direct indication of the valve's proper functioning. The other options are incorrect because they do not accurately represent the valve's normal operating conditions. Option A) does not directly test the valve's response to temperature changes. Option B) involves disassembling the valve, which is not the typical testing method. Option C) uses a heat source that may not accurately represent the valve's operating temperature range.