Pressure drop across expansion valve? - HVAC/R engineering (2025)

Hello,

I am not an HVAC designer, but I have a project that involves freon as the working fluid and a typical AC expansion valve. If the freon enters the expansion valve at some pressure and temperature in liquid state, what is the 'typical' exit pressure and temperature that must be seen downstream of the expansion valve?

I am assuming the freon goes from a room temperature liquid state to a very cold gas during this process, I just need to know the gas properties on the other side of the expansion valve.

Thank you,

- D

For a typical comfort air conditioning application you want an evaporator temperature a little above the freezing point of water.

This is actually typically controlled downstream of the evaporator by unloading the compressor, hot-gas bypass or other method of controlling the suction pressure.

In a typical AC system, expansion valves actually work to maintain a set level of superheat, not a pressure. Of course there are expansion valves that try to control pressure.

Anyway, that typical system will be somewhere around 60 psig with about 10 degrees F of superheat leaving the evaporator.

The flow of refrigerant into the evaporator is controlled by the pressure differential across the expansion device or, in the case of a thermal expansion valve, by the degree of superheat of the suction gas. Thus, the thermal expansion valve shown requires a sensor bulb located at the evaporator outlet. In any case, the flow of refrigerant into the evaporator normally increases as the evaporator load increases.
As the high-pressure liquid refrigerant enters the evaporator, it is subjected to a much lower pressure due to the suction of the compressor and the pressure drop across the expansion device. Thus, the refrigerant tends to expand and evaporate. In order to evaporate, the liquid must absorb heat from the air passing over the evaporator.

Eventually, the desired air temperature is reached and the thermostat or cold control (11) will break the electrical circuit to the compressor motor and stop the compressor.

As the temperature of the air through the evaporator rises, the thermostat or cold control remakes the electrical circuit. The compressor starts, and the cycle continues.I think thi helps you ,however if you need to know how the TXV will perform with a particular refrigerant I can help you there but i would need the which refrigerant, the SET and SCT