CARO Refrigeration Controls and Instrumentation 1 — Questions and Answers
Question 1: What is the primary purpose of a high-pressure cutout switch in a refrigeration system?
- To increase system efficiency
- To shut down the compressor when discharge pressure exceeds a safe limit (Correct answer)
- To regulate suction pressure
- To control condenser fan speed
Correct answer: To shut down the compressor when discharge pressure exceeds a safe limit
A high-pressure cutout switch protects the compressor and system by automatically shutting down the compressor when discharge pressure rises above a preset safe limit.
Question 2: Which instrument is used to measure both suction and discharge pressures simultaneously on a refrigeration system?
- A thermometer
- A manometer
- A manifold gauge set (Correct answer)
- A hygrometer
Correct answer: A manifold gauge set
A manifold gauge set has two gauges — a low-side (blue) for suction pressure and a high-side (red) for discharge pressure — allowing both readings at the same time.
Question 3: What does a solenoid valve do in a refrigeration control circuit?
- Measures refrigerant temperature
- Controls refrigerant flow by opening or closing electrically (Correct answer)
- Regulates compressor speed
- Monitors oil pressure
Correct answer: Controls refrigerant flow by opening or closing electrically
A solenoid valve is an electrically operated valve that opens or closes to control the flow of refrigerant in response to an electrical signal from the control system.
Question 4: A thermostatic expansion valve (TXV) senses which two conditions to regulate refrigerant flow?
- Suction pressure and oil level
- Evaporator outlet temperature and suction pressure (Correct answer)
- Discharge temperature and condenser pressure
- Compressor speed and refrigerant charge
Correct answer: Evaporator outlet temperature and suction pressure
The TXV uses a sensing bulb at the evaporator outlet and an external equalizer sensing suction pressure to maintain a constant superheat and regulate refrigerant flow.
Question 5: What is the function of an oil pressure safety switch on an ammonia compressor?
- To maintain refrigerant charge
- To shut down the compressor if oil pressure falls below a safe minimum (Correct answer)
- To regulate discharge temperature
- To monitor refrigerant purity
Correct answer: To shut down the compressor if oil pressure falls below a safe minimum
The oil pressure safety switch monitors lubrication oil pressure and trips the compressor off if pressure drops below the minimum required to protect compressor bearings.
Question 6: What does a pressure-temperature (PT) chart help a refrigeration operator determine?
- Compressor amperage draw
- The saturation temperature corresponding to a measured refrigerant pressure (Correct answer)
- Evaporator airflow velocity
- Oil viscosity at operating temperature
Correct answer: The saturation temperature corresponding to a measured refrigerant pressure
A PT chart lists the corresponding saturation temperature for each pressure of a given refrigerant, allowing operators to determine if the system is operating at the correct conditions.
CARO Refrigeration Controls and Instrumentation 1
What is the primary purpose of a high-pressure cutout switch in a refrigeration system?