CRST CRST Electrical Systems & Controls 1 — Questions and Answers
Question 1: What is the standard voltage for a single-phase residential refrigeration compressor in the US?
- 115V or 230V (Correct answer)
- 208V or 460V
- 480V or 600V
- 24V or 48V
Correct answer: 115V or 230V
Single-phase residential refrigeration compressors in the US typically operate on 115V or 230V circuits.
Question 2: What device protects a compressor motor from overheating by interrupting power when winding temperature is excessive?
- Internal overload protector (Correct answer)
- Crankcase heater
- Start capacitor
- Run capacitor
Correct answer: Internal overload protector
An internal overload protector (thermal overload) senses motor winding temperature and opens the circuit to prevent damage from overheating.
Question 3: In a refrigeration control circuit, what is the primary function of a thermostat?
- Cycle the compressor on and off to maintain set temperature (Correct answer)
- Regulate refrigerant flow rate
- Control fan motor speed
- Measure system pressure
Correct answer: Cycle the compressor on and off to maintain set temperature
The thermostat senses space or product temperature and cycles the compressor on and off to maintain the desired set point.
Question 4: What type of capacitor provides an extra boost of starting torque for a PSC or CSCR compressor motor?
- Start capacitor (Correct answer)
- Run capacitor
- Film capacitor
- Electrolytic capacitor
Correct answer: Start capacitor
A start capacitor provides a high momentary capacitance to boost starting torque and is switched out of the circuit once the motor reaches operating speed.
Question 5: Which electrical test instrument is used to measure the insulation resistance of a compressor motor winding to ground?
- Megohmmeter (megger) (Correct answer)
- Clamp-on ammeter
- Digital multimeter
- Oscilloscope
Correct answer: Megohmmeter (megger)
A megohmmeter (megger) applies a high DC voltage to measure insulation resistance in megohms, detecting winding-to-ground faults.
Question 6: What is the purpose of a crankcase heater on a refrigeration compressor?
- Prevent refrigerant migration into the oil during off cycle (Correct answer)
- Heat the suction line to prevent liquid slugging
- Warm the discharge gas before it enters the condenser
- Preheat the motor windings before start-up
Correct answer: Prevent refrigerant migration into the oil during off cycle
A crankcase heater keeps the compressor oil warm during the off cycle to prevent refrigerant from migrating and diluting the lubricant.
CRST CRST Electrical Systems & Controls 1
What is the standard voltage for a single-phase residential refrigeration compressor in the US?