The Hotline: 09/05/2005

September 1, 2005
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Charging A System

QUESTION:
From ACHR Student, Palm Springs, Calif.

What is the proper method to correctly charge a water-cooled R-22, 10-ton unit with a thermostatic expansion valve?

ANSWER:
By Gene Silberstein
Consulting Engineer
Whitestone, N.Y.

In order to properly charge a water-cooled air conditioning system, there must be proper water flow through the condenser as well as proper airflow across the evaporator coil. If the system has continuous water flow through the condenser, make certain that the cooling tower is operational and that water is flowing through the waterside of the coil.

There should be approximately 30 gallons per minute flowing through the condenser for your 10-ton system (3 gallons per minute per ton). If the system is equipped with a water-regulating valve, there will be no water flow through the condenser coil when the system is in the off position.

Once proper water flow and airflow have been established and the system has been properly leak tested and evacuated, you can begin adding refrigerant to the system. With the system in the off position, you can have an initial charge of liquid refrigerant through the high side of the system. You might want to temporarily jump out the low-pressure control to keep the compressor operating during the charging process. After starting the system, add refrigerant slowly until the desired pressures are reached.

On a properly charged water-cooled air conditioning system, the water entering the condenser coil should be approximately 85 degrees F and the temperature of the water leaving the condenser should be around 95 degrees. That is a 10 degrees difference between inlet and outlet temperatures.

If the temperature split is much less than 10 degrees, chances are that the system requires more refrigerant. The evaporator saturation temperature should be around 40 degrees (68.5 psig) and the high pressure should be in the range of 200 psig. The head pressure will vary somewhat from system to system.

If the system has a water regulating valve, the valve should be opening and closing in response to the changing head pressure. Also remember to remove the jumper on the low-pressure switch if you jumped it out during the changing process.

Once the system is charged, the temperature split across the evaporator should be in the range from 17 degrees to 20 degrees, meaning that the supply air should be 17 degrees to 20 degrees cooler than the air returning to the unit.

If you have a technical question, fax it to 847-622-7266 or submit it online by visiting The News' Extra Edition page and clicking on The Hotline link in the left-hand column.

Publication date: 09/05/2005

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