Sight Glass: Description and Operation

- A sight glass is located on the output side of the dryer bottle through which the refrigerant flows and is used to indicate the condition of the refrigerant charge. A clear sight glass normally indicates the system has a correct charge of refrigerant. It may also indicate the system has a complete lack of refrigerant. This will be accompanied by a lack of any cooling action by the evaporator. Also the system may be overcharged, this must be verified with test gauge readings.

- Foam or a constant stream of bubbles indicates the system does not contain sufficient refrigerant. Occasional bubbles when the system is first started is normal.

- Foam or a heavy stream of bubbles indicates the refrigerant is very low. Oil streaks on the sight glass indicate a complete lack of refrigerant. A cloudy sight glass indicates that the desiccant contained in the receiver/dryer has broken down and is being circulated through the system.