Aviation Maintenance Technician, Second Class (AMT2) SWE Practice Exam

If the unit requires additional refrigerant, what will you observe in the sight glass?

Steady flow No change Bubbles will be present Vapor lock

Correct Answer:

Bubbles will be present

Explanation:

When refrigerant is needed, the sight glass will show bubbles. This happens because the pressure drop through the metering device causes some of the liquid refrigerant to flash into vapor as it passes the sight glass. In a properly charged system, the sight glass generally looks clear with a steady flow of liquid and little to no bubbling. Vapor lock isn’t the typical observation here; it would imply a blockage or obstruction due to vapor buildup, not just undercharge.

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