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Recommended Guidelines for Servicing

Charging an Air Conditioning System (New or Completely Empty)

Notes:

1) The ambient must be above 60 degrees Fahrenheit to evacuate and charge an air conditioning system. The refrigerant tank may be placed in a pail of warm water to raise the tank pressure to facilitate charging. Tank pressure must be higher than system pressure to charge system. The typical tank pressure for charging is 40-100 psi.

2) The refrigerant service hoses must have shutoff valves within 12” of the end of the service hose to be attached to the A/C system to be serviced.

Caution:

Refrigerant is under pressure. Use safety goggles to prevent eye injury and gloves to prevent frostbite. Do not wear loose clothing that may get caught in moving parts.


The following steps will describe how to charge an R-12 or R-134a air conditioning system that uses a receiver drier with a sight glass using the vapor only charging method.

Step 1: Remove the protective caps from the charging ports on the A/C system to be charged.

Step 2: Connect the blue low side service hose to the blue compound suction gauge on the manifold gauge set and to the suction service port on the largest line at or near the compressor on the A/C system.

Step 3: Connect the red high side service hose to the red discharge gauge on the manifold gauge set and to the discharge service port at or near the compressor on the high pressure line on the A/C system.

Step 4: Connect the yellow supply hose to the center connection on the manifold gauge set and to the suction port on the vacuum pump. Evacuate for a minimum of 45 minutes.

Step 5: Close the manifold gauge valves. Disconnect the yellow supply hose from the vacuum pump and connect it to the refrigerant tank.

Step 6: Purge any non-condensable (air) out of the yellow supply hose (refrigerant tank to manifold gauge set).

Step 7: Place the bulk refrigerant tank on a certified scale to either weigh in the specified amount or refrigerant or to record the amount of refrigerant the technician puts into the system for future reference.

Step 8: Open the blue low side valve a little at first to allow the refrigerant to enter the system slowly, then open the low side valve all the way. Do not open the high side valve. If you were to open it and forget to close it when the machine is started and the air conditioner is turned on, the high side pressure could cause the refrigerant tank to explode! Observe the gauges, the low side and the high side should equalize at the same pressure as the refrigerant tank.

Step 9: Check for leaks with a leak detector. If leaks are found, correct the problem and if necessary go back through the preceding steps before continuing on to step #10.

Step 10: Start the machine and turn the air conditioning on to its maximum setting – toggle switch set to air conditioning, fans on high, thermostat set to maximum cool and the doors and windows open.

Step 11: Monitor the scale as to amount of refrigerant charge that has been pulled into the system. When the specified amount for the system is reached, close the valve on the refrigerant tank then the valve on the gauge set.

Step 11a: If the charge amount is unknown see Method: Seat-of-Pants Vapor Charging.

Step 12: Allow the system to run for three-five minutes. Place a thermometer in the louver closest to the blower motor. Record louver temperature, ambient temperature, and pressures for future reference. Check the refrigerant sight glass on the receiver drier. The sight glass can be clear or milky but should not have a steady stream of large bubbles circulating through it. Large bubbles can indicate a contaminated refrigerant charge (air) or insufficient charge. Follow method as describe in “Seat-of-Pants Vapor Charging “ section to determine whether the refrigerant charge is low.

Terex Crane Typical Charge Amounts for Kenway units are as follows:
(Note: compressors supplied with Kenway systems have sufficient oil in them for the entire system)

RT and Upper systems: 2.0 lbs of 134a refrigerant

CD 100 and 200 series: approx. 3.0 lbs of 134a refrigerant

Trucks or lowers: approx. 2.75 lbs of 134a refrigerant

Method: Seat of the Pants Vapor Charging

The theory for this method is, when a TXV/receiver-drier system goes into overcharge, the RD is completely full of liquid refrigerant so any additional refrigerant added to the system will liquefy and back up into the condenser coil. This decreases the amount of condenser used for condensing. In order to remove the heat generated from the evaporator, the discharge pressure must increase and since the liquid refrigerant is in the condenser longer it is subcooled more. Under laboratory type conditions, factory charges are determined by measuring subcooling and other system parameters,

Many AC technicians have very good luck charging R-134a systems without measuring subcooling. They basically charge a system like an R-12 system but carefully monitor the discharge pressure.

Since in ambient temperatures higher then 80° F, the sight glass of the receiver drier may not become clear, the technician watches for the bubble size reduction.

If the sight glass clears, he will add an additional .5 to 1.0 lbs depending on size of the receiver drier. If the discharge gauge reading should jump and remains elevated, he will need remove some refrigerant to restore the discharge pressure reading.

If the sight glass doesn’t clear, he will gradually add refrigerant and monitor the discharge pressures, when the pressure creeps up 5-10 psi he will stop and sometimes recover some of the refrigerant.

Care must be taken that no other factors are affecting the discharge pressure. An example is the technician is charging in a garage which continuously warms up during the charging process. The discharge reading gauge reading will climb as a result of the ambient temperature change.

Conclusion

This method relies on monitoring charges in a measurable AC system parameter. The technician must use his knowledge and experience to make a judgment, which takes in the affects of environmental changes during the charging process to determine whether the system is properly charged.

Another resource for technicians to obtain information is the Mobile Air Conditioning Society.