NATE Heat Pumps 3

Question 1

What is a typical symptom of an overcharged heat pump during cooling mode?

Accepted Answer

High suction pressure and high discharge pressure

Answer

Overcharge floods the evaporator with excess liquid refrigerant, raising suction pressure, and increases condenser load, raising discharge pressure.

Question 2

During defrost mode, why does the indoor electric heat strip energize?

Accepted Answer

To temper the cool air being delivered while the system is in cooling mode for defrost

Answer

During defrost the refrigerant cycle reverses to cooling mode, delivering cold air indoors; auxiliary strips energize to prevent occupant discomfort.

Question 3

A heat pump's outdoor unit is making a hissing noise and the reversing valve solenoid is energized. What is the most likely cause?

Accepted Answer

Reversing valve internal bypass (leaking internally)

Answer

An internally leaking reversing valve allows high-pressure refrigerant to bypass to the low-pressure side, causing a hissing sound.

Question 4

What is the recommended method for charging a heat pump system in heating mode?

Accepted Answer

Charge by subcooling measured at the outdoor coil liquid line

Answer

In heating mode, the outdoor coil is the condenser, so subcooling at the outdoor liquid line is the correct charging method.

Question 5

Which component on a heat pump prevents refrigerant from backing up into the compressor during the off cycle?

Accepted Answer

Accumulator

Answer

The accumulator collects liquid refrigerant on the suction side during shutdown and prevents liquid slugging when the compressor restarts.

NATE - North American Technician Excellence Practice Test