FREE 313D Troubleshooting and System Diagnosis Questions and Answers

Question 1

A technician is called for a no-cool complaint and finds the suction pressure is unusually low, near 0 psig, and the head pressure is also significantly lower than normal.
The suction line at the outdoor unit feels warm to the touch.
What is the most likely cause?

Accepted Answer

Severe refrigerant leak or empty system

Answer

Failed condenser fan motor

Answer

Non-condensables in the system

Answer

A major system overcharge

Question 2

A technician is troubleshooting a compressor that hums but fails to start. After safely discharging the capacitors, a multimeter with a capacitance function is used to test the dual-run capacitor, which is rated for 45/5 MFD. The reading between the 'C' (Common) and 'HERM' (Hermetic) terminals is 22 MFD. What is the correct course of action?

Accepted Answer

Replace the dual-run capacitor

Answer

Add a hard start kit to assist the compressor

Answer

Replace the compressor contactor

Answer

Check for a grounded compressor winding

Question 3

During a maintenance check, a technician observes frost forming on the evaporator coil, and the suction line is sweating heavily all the way back to the compressor. Manifold gauge readings show normal head pressure but higher-than-normal suction pressure. Which of the following is the most probable cause?

Accepted Answer

Poor indoor airflow across the evaporator

Answer

Low refrigerant charge

Answer

A restricted liquid line filter drier

Answer

A stuck-open metering device

Question 4

A technician suspects that a system has been contaminated with non-condensables, such as air. Which of the following is the most reliable method to confirm this diagnosis?

Accepted Answer

Comparing the condenser's saturation temperature (from the gauge) to the ambient temperature after the system has been off for several hours.

Answer

Observing an unusually high superheat reading at the evaporator outlet.

Answer

Measuring a very low amp draw on the compressor while the unit is running.

Answer

Noticing that the suction line is colder than usual.

Question 5

A customer reports their AC is blowing air, but it is not cool. The technician verifies the indoor blower and outdoor condenser fan are running, but the compressor is not. A distinct 'clicking' sound is heard from the outdoor unit every few minutes. The 'clicking' is most likely caused by which component?

Accepted Answer

The compressor's internal overload protector

Answer

The thermostat cycling on and off

Answer

A faulty condenser fan motor relay

Answer

The main power disconnect

Question 6

While diagnosing a system with a TXV, a technician measures a consistently high superheat and low suction pressure. The subcooling measured at the condenser outlet is found to be normal to high. Which of the following is the most probable fault?

Accepted Answer

The TXV sensing bulb has lost its charge

Answer

Inefficient compressor valves

Answer

The system is overcharged with refrigerant

Answer

The condenser coil is dirty and restricted

A technician is called for a no-cool complaint and finds the suction pressure is unusually low, near 0 psig, and the head pressure is also significantly lower than normal.The suction line at the outdoor unit feels warm to the touch.What is the most likely cause?

A technician is called for a no-cool complaint and finds the suction pressure is unusually low, near 0 psig, and the head pressure is also significantly lower than normal.
The suction line at the outdoor unit feels warm to the touch.
What is the most likely cause?