True or false: if pressure readings are far apart, are there contaminants in the refrigerant?

• A. True
• B. False
• C. Not determinable
• D. Always true

Answer: (A)

When refrigerant purity is in doubt, the pressures you measure in the system don’t line up with the expected pattern for a clean charge. In a properly charged, pure refrigerant system, high-side and low-side pressures relate to the current temperatures and the refrigerant’s pressure–temperature chart. If you see the readings on the two sides are far apart from what that relationship predicts, it signals something off in the mixture.

Contaminants such as moisture, air/non-condensables, or extra oil disrupt heat transfer and the phase behavior of the refrigerant. This often pushes head pressure higher or alters the evaporating pressure, widening the difference between the high-side and low-side readings. So a large pressure differential is a common sign that contaminants may be present and warrants further checking. Keep in mind it’s a diagnostic clue, not a definitive proof, and should be followed up with additional tests.