313D Troubleshooting and System Diagnosis 2

Question 1

A technician measures suction pressure significantly above normal and discharge pressure below normal on a residential split system. What is the most likely cause?

Accepted Answer

Compressor valve failure

Answer

Refrigerant overcharge

Answer

Restricted liquid line filter-drier

Answer

Low refrigerant charge

Question 2

During a service call, a homeowner reports the system runs continuously but never reaches setpoint. The evaporator coil is partially frosted. What should the technician check first?

Accepted Answer

Airflow across the evaporator coil

Answer

Thermostat calibration

Answer

Condenser fan motor

Answer

Compressor amperage draw

Question 3

A technician finds the high-pressure switch tripping repeatedly on a hot day. Condenser coil appears clean. What is the next most likely cause?

Accepted Answer

Condenser fan motor failure or reduced airflow

Answer

Low refrigerant charge

Answer

Metering device restriction

Answer

Compressor short cycling

Question 4

What does a high superheat AND high subcooling reading together most likely indicate?

Accepted Answer

Restriction in the liquid line or metering device

Answer

Refrigerant overcharge

Answer

Refrigerant undercharge

Answer

Compressor valve failure

Question 5

A technician suspects a refrigerant leak. After recovering and recharging, what is the correct procedure before returning the system to service?

Accepted Answer

Pressurize with nitrogen and perform a leak test

Answer

Immediately evacuate to 500 microns and recharge

Answer

Run the system and monitor pressures for 30 minutes

Answer

Add UV dye and charge with refrigerant to find the leak location

Question 6

A residential system has correct refrigerant charge but the supply air temperature differential (delta-T) is only 10°F instead of the expected 16–22°F. What is the most likely cause?

Accepted Answer

Excessive airflow across the evaporator

Answer

Overcharge of refrigerant

Answer

Refrigerant undercharge

Answer

Liquid line restriction

Question 7

When using an electronic leak detector and no leak is found at suspected areas, what technique should the technician use next?

Accepted Answer

Use UV dye and a UV light to locate the leak

Answer

Recover all refrigerant and pressure test with nitrogen

Answer

Increase system pressure by adding refrigerant

Answer

Replace the entire refrigerant circuit