ESCO Commercial Refrigeration Practice Test

Bubbles or foaming in the compressor's oil sight glass are an indication of which condition?

Liquid refrigerant in the oil Air in the oil Contaminated oil Normal oil condition

Correct Answer:

Liquid refrigerant in the oil

Explanation:

Foaming in the oil sight glass means liquid refrigerant is present in the oil. When refrigerant in liquid form mixes with the oil, it tends to flash to vapor as it circulates, creating bubbles. This foaming indicates the oil is being contaminated by refrigerant, which reduces lubrication and can lead to bearing wear. It usually points to issues with refrigerant separation or migration into the crankcase (such as overcharge, faulty oil separator, or leaks), rather than a normal condition. Air in the oil would show different gas pockets but isn’t the same foaming effect, and contaminated or normal oil would not explain persistent foaming.

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