Thermo King – Overcharge Test

Purpose: To check a unit suspected to be overcharged.
1. Install a calibrated gauge manifold.
2. Operate the unit in high speed cool five minutes or more to reduce box temperature to 60 F (16 C) or cooler. If the sight glass is full and the ball is at the top of the sight glass, the unit may be overcharged.
3. Observe the discharge pressure. Cover the condenser and increase discharge pressure 75 to 100 psig.
4. If the ball drops, the unit is not overcharged. Test need not be continued.
5. Remove the condenser cover to rapidly reduce the discharge pressure.
6. Observe the sight glass and discharge pressure.
7. The ball should move and the liquid level begin to drop by the time the discharge pressure drops 50 psig.
NOTE: The ball and liquid level will rise when discharge pressure stabilizes.
8. If the ball will not move or liquid level will not drop, the unit likely has an overcharge. Recover refrigerant, evacuate, dehydrate and weigh in a new charge. See “Adding Refrigerant by Weight to an Evacuated, Non-Operating Unit” on page 19.

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