Originally used on Chrysler vehicles, the H valve or block type expansion valve as it is referred replaces the conventional Thermostatic Expansion Valve (TXV). Besides the appearance of the valve, the biggest difference is that the H Valve eliminates the external capillary tube sensing bulb that is used on conventional expansion valves. The low pressure vapor refrigerant temperature is sensed as it passes through the expansion valve as it’s being returned to the compressor. The ‘H’ Valve expansion valve is typically attached right at the inlet of the evaporator.

Like any other expansion valve, the purpose of the valve is to provide an engineered restriction in the flow of refrigerant through the A/C system. By restricting the refrigerant flow, the valve takes high pressure liquid refrigerant from the condenser and changes it to low pressure (and low temperature) liquid refrigerant before it enters the evaporator.