While operating an R-22 single acting compressor system, oil foaming in the crankcase is most likely caused by a:

• A. Sudden drop in crankcase pressure
• B. Overfilling of oil
• C. High discharge temperature
• D. Low ambient temperature

Answer: (A)

Oil foaming in the crankcase happens when refrigerant vapor gets into the oil and forms bubbles, which disrupts lubrication. A sudden drop in crankcase pressure causes refrigerant to flash into vapor inside the oil, producing foam. This foaming reduces the oil’s ability to lubricate moving parts and can lead to wear or damage in the compressor.

The other scenarios aren’t as likely to cause foaming: overfilling the oil can cause aeration, but it doesn’t trigger the rapid vapor formation that a pressure drop does; very high discharge temperature tends to degrade the oil rather than generate foam; and low ambient temperature doesn’t promote foaming in the crankcase.