Refrigeration Controls and Instrumentation Flashcards
6 cards from real CARO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Refrigeration Controls and Instrumentation flashcards as text
What is superheat in a refrigeration system, and where is it measured?
Answer: The temperature of refrigerant vapor above its saturation temperature, measured at the evaporator outlet
Superheat is the degrees of temperature a refrigerant vapor has above its saturation point, and it is measured at the evaporator outlet to ensure no liquid enters the compressor.
A low-pressure controller on an ammonia system is set to cut out at a specific suction pressure. What does a cut-in pressure setting represent?
Answer: The pressure at which the compressor restarts after a low-pressure shutdown
The cut-in pressure is the suction pressure at which the low-pressure controller closes and allows the compressor to restart after conditions have returned to acceptable levels.
What is subcooling and why is it beneficial in a refrigeration system?
Answer: Cooling liquid refrigerant below its saturation temperature to increase system capacity and prevent flash gas
Subcooling cools liquid refrigerant below its condensing temperature, increasing the system's net refrigerating effect and preventing flash gas in the liquid line.
Which control device is typically used to maintain a constant evaporating temperature by regulating suction pressure?
Answer: Evaporator pressure regulator (EPR)
An evaporator pressure regulator (EPR) maintains a minimum evaporating pressure, which controls the evaporating temperature in multi-temperature or product-protection applications.
What is the purpose of a head pressure control valve in cold weather operation?
Answer: To maintain sufficient condensing pressure so the expansion device operates correctly during cold weather
Head pressure control valves ensure condensing pressure does not drop too low in cold ambient conditions, which would starve the expansion valve of adequate liquid pressure.
An ammonia system's suction pressure gauge reads 0 psig. What approximate evaporating temperature does this correspond to for ammonia (R-717)?
Answer: -28°F
For ammonia (R-717), 0 psig (atmospheric pressure) corresponds to a saturation temperature of approximately -28°F, which is its normal boiling point at atmospheric pressure.