Air Conditioning Repair Refrigeration System Repair 4 — Questions and Answers
Question 1: A technician is diagnosing a system with low suction pressure, high superheat, and normal condenser performance. What is the most likely cause?
- Overcharged system
- Restricted or underfeeding metering device (Correct answer)
- Faulty compressor valves
- Non-condensables in system
Correct answer: Restricted or underfeeding metering device
A restricted or underfeeding metering device starves the evaporator of refrigerant, causing low suction pressure and high superheat simultaneously.
Question 2: What is the purpose of a crankcase heater on a compressor?
- Warm refrigerant before it enters the compressor
- Prevent refrigerant from migrating into and diluting the compressor oil during off cycles (Correct answer)
- Heat the discharge line to prevent freeze-up
- Maintain oil viscosity during operation
Correct answer: Prevent refrigerant from migrating into and diluting the compressor oil during off cycles
A crankcase heater keeps the compressor warm during the off cycle to prevent refrigerant from migrating and mixing with the oil, which could cause slugging on startup.
Question 3: When using an electronic leak detector on an HFC system, which type of sensor is most appropriate?
- Heated diode (heated pentode)
- Infrared sensor (Correct answer)
- Ultrasonic detector
- Halide torch
Correct answer: Infrared sensor
Infrared sensors are highly accurate for HFC refrigerants and are not destroyed by exposure to refrigerant the way heated diode sensors can be.
Question 4: A system using a fixed orifice metering device shows high suction pressure in winter. What adjustment is typically required?
- Add more refrigerant charge
- Install a larger orifice or piston
- Replace with a TXV (Correct answer)
- Clean the condenser coil
Correct answer: Replace with a TXV
Fixed orifice devices cannot modulate with changing conditions; replacing with a TXV allows proper refrigerant metering across varying outdoor temperatures.
Question 5: What symptom would a technician observe if the reversing valve on a heat pump is stuck in the heating position?
- No cooling in summer, heating works normally (Correct answer)
- No heating or cooling available
- Cooling and heating work but efficiency is low
- Compressor overheats only in heating mode
Correct answer: No cooling in summer, heating works normally
If the reversing valve is stuck in heating mode, the system will heat in both summer and winter, providing no cooling when switched to cooling mode.
Question 6: Which condition is indicated by oil streaks or staining around refrigerant line fittings and joints?
- Normal oil migration through the system
- Refrigerant and oil leak at that location (Correct answer)
- High oil concentration in the refrigerant
- Condensation from humidity
Correct answer: Refrigerant and oil leak at that location
Oil streaks at joints indicate refrigerant is leaking there, since refrigerant oil escapes along with refrigerant gas through any leak point.
Question 7: A technician measures discharge superheat of 90°F. Normal discharge superheat is 50–70°F. What does this indicate?
- Overcharged system
- Low suction superheat
- Insufficient refrigerant or low suction pressure (Correct answer)
- Condenser subcooling is too high
Correct answer: Insufficient refrigerant or low suction pressure
Excessively high discharge superheat indicates the compressor is compressing very hot, low-density gas, typically caused by low refrigerant charge or high suction superheat.
Air Conditioning Repair Refrigeration System Repair 4
A technician is diagnosing a system with low suction pressure, high superheat, and normal condenser performance.
What is the most likely cause?