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Refrigeration cycle practice questions

35 questions from the hvac fundamentals practice test.

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Refrigeration cycle practice test

10 questions, graded as you go, with the reason for every answer. No sign-up.

What this covers

Sample questions

What leaves the outlet of the metering device and enters the evaporator?

  1. A cold low-pressure vapor with several degrees of superheat
  2. A warm high-pressure liquid with several degrees of subcooling
  3. A cold low-pressure mix of liquid and some flash gas
  4. A cold low-pressure liquid with no vapor present at all
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C. A cold low-pressure mix of liquid and some flash gas

The pressure drop across the metering device makes part of the liquid flash to vapor, which cools the rest to the evaporator saturation temperature, so a mostly liquid mixture enters the coil. It is not superheated vapor yet; superheat is only picked up near the evaporator outlet after all the liquid has boiled.

Reference: Metering devices; flash gas

Which statement correctly defines superheat?

  1. Vapor temperature above its saturation temperature at that pressure
  2. Liquid temperature below its saturation temperature at that pressure
  3. Suction line temperature minus the liquid line temperature
  4. Discharge line temperature minus the outdoor air temperature
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A. Vapor temperature above its saturation temperature at that pressure

Superheat is the sensible heat added to a vapor after it has completely boiled: measured vapor temperature minus the saturation temperature for the measured pressure. Temperature below saturation describes a liquid and is subcooling.

Reference: Superheat definition

Which statement correctly defines subcooling?

  1. Suction line temperature minus the evaporator saturation temperature
  2. Outdoor air temperature minus the liquid line temperature
  3. Condensing saturation temperature minus the outdoor air temperature
  4. Condensing saturation temperature minus the liquid line temperature
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D. Condensing saturation temperature minus the liquid line temperature

Subcooling is how far the liquid has been cooled below the saturation temperature that corresponds to the high-side pressure. Condensing temperature minus outdoor air temperature is the condenser split, which is a different measurement.

Reference: Subcooling definition

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