Air Conditioning Repair Service 5 — Questions and Answers
Question 1: A technician finds acid in the compressor oil during a burnout analysis. After replacing the compressor, which additional service step is MOST critical?
- Install a new filter drier and perform a system flush (Correct answer)
- Increase the refrigerant charge by 15%
- Replace only the Schrader valve cores
- Adjust the thermostat anticipator setting
Correct answer: Install a new filter drier and perform a system flush
Acid from a burnout contaminates the entire system, and a new filter drier with acid-absorption capability, along with flushing, is essential to prevent repeat failure.
Question 2: What is the recommended method to verify proper refrigerant charge on a fixed-orifice (piston) metering device system?
- Target a superheat of 10–18°F at the evaporator outlet under standard conditions (Correct answer)
- Check subcooling at the condenser outlet only
- Use only a sight glass to confirm clear flow
- Weigh in the factory charge and do not check further
Correct answer: Target a superheat of 10–18°F at the evaporator outlet under standard conditions
Fixed-orifice systems are charged using superheat method, typically targeting 10–18°F at the evaporator outlet to ensure proper refrigerant feed without flooding.
Question 3: During a service call, a technician confirms low refrigerant charge. Before adding refrigerant, the technician should:
- Locate and repair the leak first (Correct answer)
- Add refrigerant immediately to restore operation
- Replace the compressor as a precaution
- Increase the blower speed to compensate
Correct answer: Locate and repair the leak first
EPA regulations and good practice require finding and repairing leaks before recharging, as simply topping off a leaking system wastes refrigerant and is non-compliant.
Question 4: A condenser fan motor runs but the blade is not turning. The MOST likely cause is:
- Broken or loose fan blade set screw (Correct answer)
- Open capacitor
- Shorted motor windings
- Tripped high-pressure switch
Correct answer: Broken or loose fan blade set screw
If the motor shaft spins but the blade does not move, the fan blade's set screw or retaining hardware has failed, disconnecting the blade from the shaft.
Question 5: What is the purpose of the suction line accumulator in an air conditioning system?
- To prevent liquid refrigerant from entering the compressor (Correct answer)
- To store extra refrigerant when the system is overcharged
- To filter debris from the refrigerant
- To regulate discharge pressure
Correct answer: To prevent liquid refrigerant from entering the compressor
The accumulator is located on the suction line and holds excess liquid refrigerant, allowing only vapor to enter the compressor and preventing liquid slugging.
Question 6: A technician measures 240V at the contactor line side terminals but 0V at the load side terminals when the thermostat calls for cooling. This indicates:
- The contactor coil is not being energized or the contactor is faulty (Correct answer)
- A blown fuse on the disconnect
- A failed compressor
- Low refrigerant pressure lockout
Correct answer: The contactor coil is not being energized or the contactor is faulty
Voltage present on the line side but absent on the load side means the contactor has not closed, pointing to no control voltage at the coil or a failed contactor.
Question 7: What is the correct action if a technician suspects moisture contamination inside an air conditioning system?
- Recover refrigerant, replace the filter drier, evacuate deeply, then recharge (Correct answer)
- Add more refrigerant to dilute the moisture
- Run the system at full capacity to evaporate moisture
- Replace only the Schrader cores and recharge
Correct answer: Recover refrigerant, replace the filter drier, evacuate deeply, then recharge
Moisture must be removed by replacing the filter drier (which absorbs moisture), then performing a deep vacuum evacuation to below 500 microns before recharging.
Air Conditioning Repair Service 5
A technician finds acid in the compressor oil during a burnout analysis.
After replacing the compressor, which additional service step is MOST critical?