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SESK: Stuff Everyone Should Know · sesk.info/epa-cycle-expansion

What drops the refrigerant's pressure before it enters the evaporator?

The expansion valve, which lets the liquid expand to evaporator pressure.

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  1. The compressor
  2. The expansion valve ✔
  3. The filter-drier

Why: High-pressure liquid passes through the expansion valve, and pressure drops to evaporator pressure. Some of the liquid flashes to vapor, so the refrigerant leaves cold, as a mix of liquid and vapor.

Huh, didn't know that: In EPA's example, the mix leaving the valve is about 70 percent liquid and 30 percent vapor.

The dad joke
The expansion valve is the system's bouncer. It decides how much gets in.
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References

Answer: The expansion valve. High-pressure liquid passes through the expansion valve, and pressure drops to evaporator pressure. Some of the liquid flashes to vapor, so the refrigerant leaves cold, as a mix of liquid and vapor.

  1. Refrigeration and Heat Pump Systems, WPI lecture notes (Chapter 10) users.wpi.edu/~sullivan/ES3001/Lectures/ch10-jms.pdf
    liquid refrigerant expands to the evaporator pressure
    Checked 2026-10-10.
  2. Refrigeration 201 slides, US EPA (archived) 19january2021snapshot.epa.gov/sites/static/files/documents/Refrigeration201.pdf
    70% Liquid 30% Vapor
    Checked 2026-10-10.

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