Checking Charge by Sight Glass

LIQUID LINE SIGHT GLASS

A liquid line sight glass allows for quick, visual confirmation of refrigerant charge when the metering device is an expansion valve.

Cooling Mode

In the cooling mode, refrigerant is pressurized and cooled in the condenser. With adequate pressure and cooling the refrigerant "sub-cools" and condenses into a liquid state. This transition can be seen through the sight glass.

Heating Mode

In the heating mode, refrigerant is pressurized and cooled in the indoor coil. With adequate pressure and cooling the refrigerant "sub-cools" and condenses into a liquid state. This transition can be seen through the sight glass.

• Bubbly refrigerant would indicate refrigerant that has not fully condensed.
• A clear sight glass indicates full liquid refrigerant.*

Reasons for a bubbly sight glass:

1. Low Charge - If the system does not have enough refrigerant to generate adequate pressure, the condensation process may not take place.
2. Inadequate Cooling - If enough heat is not being removed at the condenser, the refrigerant may not be able to change to liquid.
3. No Expansion Valve - Some systems use an orifice or cap tube as the metering device. With these systems, a sight glass is not an effective way to check charge.

* Allow the system to run for at least 10 minutes before attempting to determine charge by the sight glass.

* Be cautious not to confuse a clear sight glass with an empty sight glass.