What is the likely cause?
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
On an idle R-11 chiller, the refrigerant and water are both at 72 °F, but the gauge reads well above the pressure-temperature chart value for 72 °F. What is the likely cause?
- A refrigerant undercharge
- Too much oil in the sump
- Chilled water flowing too fast
- Air or other noncondensables in the chillerCorrect answer
Why “Air or other noncondensables in the chiller” is correct
With liquid and vapor present at a steady temperature, the pressure should match the P-T chart for that refrigerant. Extra pressure above that value comes from gases that do not condense, which the purge unit should remove.
Source: EPA: Test Topics
Why the other answers are wrong
- A refrigerant undercharge — An undercharge does not raise standing pressure above the saturation value.
- Too much oil in the sump — Oil level does not push pressure above the P-T value.
- Chilled water flowing too fast — The chiller is idle, and water flow does not raise pressure above saturation.
Practice more of this
More EPA 608 Type III practice questions, or see every EPA 608 practice test.
Unofficial, not affiliated with the EPA or any EPA-approved certifying organization. Questions are original practice written from public EPA material, not real exam questions.