HVAC Air Handler Units and Coils 5

Question 1

What is the correct procedure if an evaporator coil is found to be completely iced over during a service call?

Accepted Answer

Turn the system to fan-only mode to thaw the coil before diagnosing the cause

Answer

The coil must be allowed to thaw completely (using fan-only mode) before diagnosis because testing a frozen system gives inaccurate readings and won't reveal the true cause.

Question 2

What is the difference between a 'chilled water coil' and a 'direct expansion (DX) coil' in an air handler?

Accepted Answer

Chilled water coils circulate cold water through tubes; DX coils use refrigerant directly

Answer

A chilled water coil uses chilled water pumped from a chiller as its cooling medium, while a DX coil has refrigerant flowing directly through its tubes from the compressor system.

Question 3

What is the purpose of 'subcooling' in a condenser coil?

Accepted Answer

To cool liquid refrigerant below its condensing temperature to prevent flash gas in the liquid line

Answer

Subcooling cools liquid refrigerant several degrees below its condensing temperature, preventing it from flashing into vapor in the liquid line before reaching the expansion device.

Question 4

What is a 'multi-speed' blower motor and what advantage does it provide?

Accepted Answer

A motor with multiple windings that can run at different RPMs to match varying system demands

Answer

A multi-speed blower motor has multiple tapped windings that allow it to operate at different fixed speeds, enabling adjustment for heating vs. cooling or different duct system conditions.

Question 5

When replacing an evaporator coil, why must the refrigerant circuit be properly evacuated before recharging?

Accepted Answer

To remove air and moisture that entered the system during the open coil replacement

Answer

Evacuation removes air and moisture that entered the open refrigerant system during coil replacement; moisture in the system can cause acid formation, freezing at the metering device, and compressor damage.

HVAC - Heating, Ventilation, and Air Conditioning Practice Test

HVAC - Heating, Ventilation, and Air Conditioning Practice Test

HVAC Air Handler Units and Coils 5