RSES Expansion Devices 2

Question 1

What happens to refrigerant pressure as it passes through a thermostatic expansion valve (TXV)?

Accepted Answer

Pressure drops from high-side to low-side pressure

Answer

The TXV creates a pressure drop that allows the refrigerant to flash from liquid to a low-pressure mixture entering the evaporator.

Question 2

A TXV with an external equalizer senses evaporator pressure at which location?

Accepted Answer

At the evaporator outlet

Answer

The external equalizer line connects to the evaporator outlet, allowing the valve to sense actual evaporator pressure rather than inlet pressure.

Question 3

Which condition would cause a TXV to be in the fully closed position?

Accepted Answer

Low superheat at the bulb location

Answer

Low superheat indicates excessive liquid refrigerant at the evaporator outlet, causing the TXV bulb pressure to drop and close the valve.

Question 4

What is the typical superheat setting range for a TXV used in air conditioning applications?

Accepted Answer

8-12°F

Answer

Most air conditioning TXVs are factory set for 8-12°F superheat to ensure full evaporator use while protecting the compressor.

Question 5

An automatic expansion valve (AEV) maintains constant:

Accepted Answer

Evaporator pressure

Answer

The AEV modulates to maintain a constant evaporator (low-side) pressure regardless of load changes.

(RSES) Refrigeration Service Engineers Society Certification Practice Test