WHEEL & BRAKE GP 3377950 - Caterpillar

Charging the System
Pressure cannot accurately be used to charge the air conditioning system
An accurate refrigerant charge may only be determined by weight. Several variables affect the pressure and the variables cause the system to be incorrectly charged.Compressor Speed - :
The rate of refrigerant that is pumped by the compressor will affect the pressure that is built by the compressor.Air Flow and Air Temperatures Through the Condenser and Evaporator - :
The amount of air flow and the temperature of the air that is moving through the condenser or evaporator will affect the pressures that are seen at the compressor. Blockages in the stream of air flow will affect the amount of heat that is rejected from the refrigerant or absorbed into the refrigerant. This process affects the working pressures.Ambient Temperature - :
Pressures are affected by ambient air temperature and solar load to the cab.
Temperature that is around hoses and other components affect the ambient temperature. As the engine heats up, some of the heat is absorbed into the refrigerant during the refrigerant ride through the hoses and components. The pressure in the compressor can be greatly affected by the heat that is absorbed in many locations.
Ambient temperatures will change throughout the operation of the AC, resulting in constant pressure fluctuations.Internal Blockages - :
Blockages that are at different locations in the refrigerant circuit will affect the pressures and the blockages will cause various concerns with pressure and fluctuations.
Note: Do not add or remove part of the refrigerant.Note: Never charge liquid or gas through the discharge side (high side) of the system when the engine is in operation.
In an expansion valve system which uses poly alkaline glycol (PAG), the sight glass is not a reliable way to determine the system charge.
Note: For expansion valve systems that contain PAG oil, the sight glass cannot be used for charging the system. In order to achieve a full charge for the system, the refrigerant must be recovered from the system and the system must be evacuated. After the system has been recovered and the system has been evacuated, charge the system with the correct amount of refrigerant. This process is the only procedure that is recommended. Refer to the Specifications, "System Capacities for Refrigerant" section for the proper capacity. Also, refer to the Systems Operation, "Identifying the Air Conditioning System" section.Note: Before you charge the system, these important items should be checked.
Condenser and evaporator
Inspect the condenser and inspect the evaporator for foreign material such as dirt, insects, plastic bags, and so on, that would inhibit air flow.
With condensers that are mounted on the roof and with remote mounted condensers, always check that both fan motors are running. Check for restrictions. A clean condenser will lead to improved life for the compressor.
Check for a loose belt on the compressor.
Clean the fresh air filter and clean the recirculation filter.
Check the moisture indicator on either the