307D, 311D, 312D, 313D, 315D, 318D, 319D, 320D, 323D, 324D, 325D, 326D, 328D, 329D, 330D, 336D, 340D, 345D, 349D, 374D, 390D and M325D Excavators Air Conditioning and Heating General Troubleshooting Information Caterpillar


General Troubleshooting Information
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------ 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.


  • Low refrigerant charge will cause a loss of cooling ability and a loss of lubrication in the compressor, which will result in failure of the compressor.

  • Overcharge of refrigerant will cause a loss of cooling ability. A system that is overcharged will contain excess liquid refrigerant, which will severely damage the compressor. An overcharged system will fail two times faster than an undercharged system.

  • Too much oil in the system will contribute to a low refrigerant charge.

  • A small amount of moisture will penetrate the hoses that are used in R134a systems. Change the refrigerant dryer and the desiccant annually. Moisture causes sludge and moisture results in plugged systems.

  • Gauge readings for an undercharged R134a system may appear as symptoms of overcharge under certain conditions. This occurs when the ambient temperature is above 32 °C (90 °F) or in high humidity. Gauge readings that are Incorrect lead to a loss of cooling ability and failure of the compressor.

  • Refrigerant that is removed from a system cannot be weighed accurately. A 20 to 30% error can occur. The error is a result of oil that is removed from the system and a result of the inaccuracies of devices that are used for recovery.

  • Check the scale that is used for charging for accuracy after every 30 days or after every 30 uses.

  • After recovering a system, if the system pressure rises above 0 kPa (0 psi) within 5 minutes, the system must be recovered again until the pressure does not increase.

  • Frost can appear anywhere on a R134a air conditioning system. The appearance of frost does not always indicate a failure. In order to diagnose a blockage in the air conditioning system properly, the air temperature at the evaporator must be checked and pressure readings must be taken.

  • In order to check the function of the compressor, disconnect the hose from the inlet of the refrigerant dryer. Measure the pressure of suction of the compressor. The pressure should be a vacuum that is between 81 kPa (24 in Hg) to 95 kPa (28 in Hg). Do not operate the compressor for more than 2 minutes when the system pressure is below vacuum.

  • Perform regular maintenance on the refrigerant service units and change the oil in the vacuum pumps.

  • Secure lines and wires in order to prevent damage to the lines and wires.

  • The formation of black sludge deposits in the system is caused by the presence of moisture in R134a systems and by mixing charges of R134a and R12. The black sludge deposits can cause a blockage in the system.

  • The presence of white foam during recovery is normal. The foam is caused by the mixing of oil and refrigerant.

  • R134a system charges must be within 0.03 kg (1.000 oz) to .06 kg (2.000 oz) of the specified charge for the machine.

  • A drain line that is plugged or a drain line that is pinched may cause a backup of condensate and leakage into the cab.

  • Missing drain valves may cause a backup of condensate and leakage into the cab.

  • Missing drain valves will allow dust to be sucked into the evaporator coil and the heater coil.

A cab pressure of 0.05 kPa (0.200 inch of H2O) to 0.15 kPa (0.600 inch of H2O) and proper maintenance of the air conditioner filter will result in the following conditions:

  • Reduction of dust

  • Reduction of noise

  • More efficient HVAC performance

A loss of cooling ability of the system and failure of the compressor may be caused by one or more of the following conditions.

  • Low charge

  • Overcharge

  • Too much oil

  • Too little oil

  • Dirty filter or plugged filter

  • Dirty condenser or plugged condenser

  • Dirty evaporator or plugged evaporator

  • Dirty orifice tube or plugged orifice tube

  • Dirty expansion valve or plugged expansion valve

  • Too much moisture in the system

  • Missing drain valves for the evaporator

Information System:

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