How does running warm water through the tubes raise the pressure inside an idle R-11 chiller?

Leak detection · EPA 608 Type III. The correct answer, and the reasoning behind it.

Pressurizing low-pressure systems for leak tests, signs of leaks, inspections and reports.

The question

How does running warm water through the tubes raise the pressure inside an idle R-11 chiller?

• AWarming the refrigerant raises its saturation pressureCorrect answer
• BThe water mixes with the refrigerant and adds volume
• CThe warm water drives the compressor to build pressure
• DThe heat condenses air out of the shell

Why “Warming the refrigerant raises its saturation pressure” is correct

A refrigerant's pressure follows its temperature. Warming the R-11 in the shell boils more of it into vapor and lifts the pressure above atmospheric, so leaks push refrigerant outward. This is why controlled hot water is the preferred way to pressurize a low-pressure chiller.

Source: EPA: Test Topics

Why the other answers are wrong

• The water mixes with the refrigerant and adds volume — The water stays inside the tubes and never mixes with the refrigerant.
• The warm water drives the compressor to build pressure — The compressor is off; the pressure comes from the refrigerant itself.
• The heat condenses air out of the shell — Heat does not condense air; it boils more refrigerant into vapor.

Practice more of this

More EPA 608 Type III practice questions, or see every EPA 608 practice test.