If the refrigerant warms from 70 °F to 90 °F, what happens to its pressure?

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

Purge units and pressure-temperature behaviour of low-pressure refrigerants.

The question

A closed R-123 chiller holds both liquid and vapor. If the refrigerant warms from 70 °F to 90 °F, what happens to its pressure?

• AIt goes from below to above atmospheric pressureCorrect answer
• BIt stays the same, since the chiller is closed
• CIt falls further into a vacuum
• DIt jumps to about 100 psig

Why “It goes from below to above atmospheric pressure” is correct

R-123 boils at about 82 °F at atmospheric pressure. Below that temperature its saturation pressure is a vacuum; above it, slightly positive. The same rule is why warming the refrigerant can bring a chiller above atmosphere for leak testing.

Source: EPA: Test Topics; Hudson Technologies R-123 and R-11 P-T charts

Why the other answers are wrong

• It stays the same, since the chiller is closed — Saturated refrigerant pressure follows temperature even in a closed vessel.
• It falls further into a vacuum — Warming raises saturation pressure; it does not lower it.
• It jumps to about 100 psig — R-123 at 90 °F is only slightly above atmospheric pressure.

Practice more of this

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