What is the function of expansion valve’s capillary tube in air conditioning?
The capillary tube controls the amount the expansion valve is open. As the temperature of the outlet of the evaporator increases, the expansion valve opens to allow for more refrigerant flow.
The temperature is sensed by a remote thermal bulb attached to the capillary tube of the valve. A decrease in outlet temperature will cause the valve to close, thereby restricting the flow of refrigerant.
How do you test a expansion valve?
A quick test of the expansion valve involves warming and cooling the thermal bulb and watching the change in pressures on the manifold gauge set.