Air Conditioning and Heating R-12 All Caterpillar Machines – Refrigerant System – Evacuate

------ WARNING! ------

Personal injury can result from contact with refrigerant.

This system is under pressure at all times, even if the engine is not running. Heat should never be applied to a charged system.

Contact with refrigerant can cause frost bite. Keep face and hands away to help prevent injury.

Protective goggles must always be worn when refrigerant lines are opened, even if the gauges indicate the system is empty of refrigerant.

Always use caution when a fitting is removed. Slowly loosen the fitting. If the system is still under pressure, evacuate the system recovering the refrigerant before removing the fitting.

Personal injury or death can result from inhaling refrigerant through a lit cigarette.

Inhaling air conditioner refrigerant gas through a lit cigarette or other smoking method or inhaling fumes released from a flame contacting air conditioner refrigerant gas, can cause bodily harm or death.

Do not smoke when servicing air conditioners or wherever refrigerant gas may be present.

Before any checks of the air conditioning and heating system are made, move the machine to a smooth horizontal surface. Lower all implements to the ground. Make sure the transmission is in neutral or park and that the parking brake is engaged. Keep all other personnel away from the machine or where they can be seen.


If replacement of a component is necessary or repair to a component is necessary, the refrigerant in the system must be recovered. Also, if the system has lost any charge after a long period of time, the refrigerant in the system must be recovered. It is necessary to perform the evacuating procedure in order to delete the system of all air and moisture. A complete charge must never be given to a system without first performing the evacuating procedure. Before evacuating the system, refer to the following manual.

  • Testing and Adjusting, SENR3334, “Refrigerant Leakage – Test”

  • Testing and Adjusting, SENR3334, “Refrigerant Recovery”

  • Testing and Adjusting, SENR3334, “Refrigerant Compressor Oil – Check”

If the system has been left open for more than 1/2 hour, the system has been exposed to air or moisture and a new receiver-dryer, an in-line dryer or a desiccant accumulator needs to be installed. Moisture will combine with metals in the refrigerant system and this will produce highly corrosive by-products. The by-products are oxides, iron hydroxide, and aluminum hydroxide. Moisture can freeze the expansion valve and moisture can freeze the orifice tube. If there is water in the system the water must be removed. Remove the water by pumping the system with a vacuum pump and boiling the water. Refer to Table 1 that is shown below.

The time for the evacuation process will increase under the following conditions:

  • The air conditioning system has been rebuilt.

  • The air conditioning system has been flushed.

  • The air conditioning system has new components.

  • The air conditioning system has been retrofitted.

Table 1
Boiling Point of Water Under Vacuum    
Temperature of Work Area (°C (°F))     Vacuum That Is Required In Order To Boil Water In An Air Conditioning System (m bar (Hg))    
38 °C (100 °F)     95 kPa (28 in Hg)    
32 °C (89.60 °F)     96.5 kPa (28.50 in Hg)    
27 °C (81 °F)     97.5 kPa (28.80 in Hg)    
21 °C (70 °F)     98.8 kPa (29.20 in Hg)    

Note: After the leak test is completed, the system must be evacuated for a minimum of 30 minutes. In order to correctly evacuate the system, the vacuum gauge must be less than three inches away from the system port. If the gauge is more than three inches away from the system port, pull a vacuum and allow the system to equalize for ten minutes. This will ensure an accurate gauge reading.


All refrigerant must be recovered before the evacuating procedure is started. Never discharge the refrigerant through the vacuum pump. Never discharge the refrigerant into the atmosphere. Always use the Refrigerant Identifier tool in order to ensure that contamination of the system does not occur.

Illustration 1 g00887430

(1) Low pressure valve

(2) High pressure valve

(3) Charging hose

(4) Compressor block fitting (discharge)

(5) Compressor block fitting (suction)

(6) Service valve (discharge)

(7) Service valve (suction)

(8) Vented exhaust valve

(9) Line from condenser

(10) Line from evaporator

  1. After the refrigerant is recovered from the system, make sure that the low pressure valve (1) and the high pressure valve (2) are closed. Disconnect the charging hose (3) of the manifold gauge set from the refrigerant service unit.
  1. Check the oil level in the vacuum pump. Refer to the Testing and Adjusting, “Refrigerant Compressor Oil – Check” for the correct procedure. Add oil if oil is needed. If contamination of the system is indicated, change the oil.
  1. Connect the electrical plug from the vacuum pump to an approved electrical outlet.
  1. Connect the charging hose (3) to the inlet fitting on the vacuum pump. Refer to Illustration 1.
  1. Open low pressure valve (1) and open high pressure valve (2) on the manifold gauge set completely. Turn the valves counterclockwise.
  1. In order to start the pump motor, turn the power switch to the ON position.
  1. In order to open the vented exhaust valve (8), turn the valve counterclockwise.

    Note: The vented exhaust valve (8) must be closed until the vacuum pump has started.

  1. Operate the vacuum pump until the low pressure gauge indicates a pressure that is between 95 kPa (28 in hg) and 98 kPa (29 in hg). After the vacuum in the system reaches a value that is between 95 kPa (28 in hg) and 98 kPa (29 in hg), close the vented exhaust valve (8). Operate the vacuum pump for a minimum of 90 minutes after the vented exhaust valve is closed. Use a 113 L/min (4 cfm) pump. Make allowances for pumps that are smaller than 113 L/min (4 cfm) cfm.

    Note: 95 kPa (28 in hg) to 98 kPa (29 in hg) is the required specification at sea level. For every 305 m (1000 ft) above sea level, decrease the required specification by 3 kPa (1 in hg). At high elevations, less vacuum is required.

  1. If the specific vacuum cannot be reached, the system may have a leak. Refer to the Testing and Adjusting, “Refrigerant Leakage – Test” section. Perform the procedures that are indicated. Repair all leaks and repeat Step 1 of the evacuating procedure.

    Note: The evacuating procedure removes air and moisture from the system. Do not use the vacuum pump primarily to indicate a system leak.

  1. After 95 kPa (28 in hg) to 98 kPa (29 in hg) vacuum has been reached and held for an additional 90 minutes, close valve (1) and close valve (2) completely. Turn the power switch on the vacuum pump to the OFF position. The maximum amount of vacuum loss in five minutes must not be more than 7 kPa (2 in hg). Excessive vacuum loss is an indication of a possible leak in the system. Refer to the Testing and Adjusting, “Refrigerant Leakage – Test” section. Perform the procedures that are indicated. Repair all leaks and repeat Step 1 of the evacuating procedure.
  1. If the vacuum loss does not exceed 7 kPa (2 in hg) in five minutes, the system is then ready for a complete charge. Refer to the Testing and Adjusting, “Refrigerant System – Charge” section. Perform the procedures that are indicated.
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