950G Series II Wheel Loader Air Conditioning and Heating Caterpillar

Introduction to Machine Air Conditioning and Service Procedures

This lesson discusses the proper precautions to use, the visual inspections to make, and the operational checks when you are servicing an air conditioner system on a machine.

Safety Precautions

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The following precautions should be followed when you are servicing air conditioning systems, operating air conditioning equipment, or handling refrigerants:

• Wear safety goggles. Refrigerant that comes in contact with the eyes can cause serious injury.

• Do not use excessive heat on refrigerant containers during the charging process. Never use direct heat. Use a container of water that does not exceed 52 °C (125 °F).

• Do not discharge refrigerant into the atmosphere. In addition to being harmful to the earth's ozone layer, Refrigerant 12 when subjected to an open flame results in a very poisonous phosgene gas.

• Always work in a well ventilated area. Inhaling refrigerant, even in small amounts, can be cumulative and cause light-headedness. Refrigerants can also cause irritation to the eyes, the nose, and the throat.

• Do not weld or steam clean an air conditioning system. Excessive pressure could build up in the system.

• Do not mix R-134a with air for the purpose of leak testing. When the R-134a is under pressure the mixture could explode.

• The high pressure gauge valve must be closed when you are charging a system while the engine is running.

• Be alert when the engine is running. Stay clear of rotating components.

• Do not recover or transfer refrigerant into a disposable tank. Always use a DOT approved tank. Look for "DOT4BA" or "DOT4BW" on the tank.

• Do not fill a storage tank to more than 80% of the gross weight rating.

Air Conditioning Performance Tests

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Visual Inspection, Engine OFF.

Correct air conditioning system performance is the number one objective whether you are conducting preventive maintenance or a major repair. When you are doing a performance test, the first step is a visual inspection of the air conditioning system components. The visual inspection is performed while the engine off.

Compressor

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The compressor drive belt may be damaged or loose. A damaged drive belt must be replaced. When you install a new belt or you are tightening a loose belt, use the Caterpillar belt tension gauge. See the Service Manual for belt tightening specifications.

Inspect the condenser for trash, dirt, and other debris that can restrict air flow. Insufficient air flow through the condenser can cause poor cooling and lead to compressor damage.

Evaporator

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The evaporator blower or the fan can only be effective when air passages are clear. Condensation traps dirt and debris on the blower side of the evaporator. The dirt and debris form a coating that restricts evaporator air flow. The coating must be removed.

Inspect the fresh air and recirculating air filters. Clean the filters or replace the filters, as needed.

Blower Motor

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Check the blower motor for satisfactory operation. Operate the blower motor at all speeds. Turn the key switch ON in order to provide power to the blower motor. Make repairs if the air flow does not increase as the control is moved from low speed to higher speeds. Make repairs if the motor is noisy and/or if the motor fails to operate in some speeds.

Air Ducts and Louver Controls

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Operate all air ducts and louver controls. The controls should move freely without sticking or binding.

Operation Checks

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When you are making the air conditioning operation checks, the engine should be at normal operating temperature and the air conditioning system must be stable.

• Install the manifold gauge set.

• Start the engine and increase the engine speed to approximately 1000 rpm.

• Turn on the air conditioning system. Move the temperature control to the MAXIMUM position. Move the fan switch to the HIGH position. Operate for 10 - 15 minutes.

• Increase the engine speed to 1300 - 1400 rpm.

• Conduct the air conditioning system operational checks.

Manifold Gauge Set

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The manifold gauge set is an important tool in checking performance, a diagnosis, and servicing of the air conditioning system. The gauge set is composed of a low side (compound) gauge (1), a manifold (2) to which the gauges are connected and a high side gauge (3). The high side hand valve (4) and low side hand valve (8) allow the system to be evacuated and serviced through the manifold.

The low side hose connector (7) and high side hose connector (5) connect the gauge manifold to the air conditioning system. The center service hose (6) connects the manifold gauge to an external source.

Manifold gauge pressures will be affected by the ambient air temperature or the outside air temperature. High side pressures are affected more than the low side pressures.

When the ambient temperature is above 21°C (70°F), the low side pressure should read from 70 to 210 kPa (10 to 30 psi), depending on the ambient temperature and the machine that is being tested. The high side pressure should read from 820 to 2075 kPa (120 to 300 psi) depending on the ambient temperature and the machine being tested.

See Table 12 in the Service Manual for Pressure Range Reference. No two systems will have the exact same manifold gauge readings. Allow for variations in pressures.

Schraeder Valve

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Schraeder valves are used to attach the manifold gauge set to the air conditioning system. Schraeder valves eliminate the need for service valves in the system. The Schraeder valves effectively seal the refrigerant that is inside the system, until the Schraeder valves are opened.

The Schraeder fitting on the high side (1) is smaller than the fitting on the low side (2). The difference in the fitting sizes is to prevent connecting the manifold gauge set to the wrong pressure side.

Schraeder Valve and Service Hose

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Illustration 10 shows a sectional view of a Schraeder valve. Illustration 10 shows a service hose with a Schraeder core depressor. As the high and/or low side pressure hose is threaded onto the Schraeder valve service port, the Schraeder core depressor in the hose depresses the pin in the center of the Schraeder valve. The valve is opened. This allows the refrigerant to flow between the manifold gauge set and the compressor. When the hose is removed, the valve closes automatically.

Manifold Gauge Set

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Illustration 11 shows a sectional view of the manifold gauge set that is used in a performance test.

The compound gauge is connected through the low side internal passage to the low side service connector. The low side service connector is connected through a hose (not shown) to the low pressure side of the air conditioning system. When the low side hand valve is closed, the compound gauge shows only the low side pressure reading.

The high pressure gauge is connected through the high side internal passage to the high side service connector. The high side service connector is connected through a hose (not shown) to the high pressure side of the air conditioning system. When the high side hand valve is closed, the high pressure gauge shows only the high side pressure reading.

The center internal passages in the manifold connect the center service connector to the low side passages and high side passages. During a performance test, the closed hand valves isolate the low side passages and the high side passages from the center service connector.

Adding Refrigerant

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Illustration 12 shows a sectional view of the manifold gauge set when you add refrigerant to the system.

Opening the low side hand valve opens the center service connector to the low side service connector and the low side gauge. Refrigerant flows into the center service connector, through the manifold gauge, and out through the low side service connector. The compound gauge registers the low side pressure during the operation.

Air Conditioning System

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With the air conditioner running, carefully check the relative temperatures at the high side and low side of the system.

High side temperature should vary from hot at the compressor discharge to warm at the expansion valve. Any sudden drop in temperature indicates a partial blockage at that point.

Low side temperature should be cool. There may be large sweating or frosting of the suction line from the evaporator to the accumulator that depends on the ambient temperature.

Evaporator Output

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With the engine speed set at 1300 to 1400 rpm, set the temperature control to the MAXIMUM cool position. Set fan switch in the HIGH position. Run the air conditioning system for 15 to 20 minutes. Place a thermometer in the blower air outlet duct and record the reading. Then, use the thermometer to read the ambient air temperature. The temperature difference between the air from the air duct and the ambient air is listed below:

Moisture Indicator

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The moisture indicator may be added to some air conditioning systems in order to aid in determining the amount of moisture that is in the system. The moisture indicator is located on the high side between the receiver-dryer and the expansion valve. The moisture indicator consists of the sight glass (1) and the indicator ring (2). The indicator ring is viewed through the sight glass.

When you check for moisture, the air conditioning system must operate for approximately 3 hours. If the indicator ring is blue, the system is dry. If the indicator ring is pink or white, the system has moisture.

The following procedure will remove all moisture from the system:

• The system refrigerant must be recovered and recycled.

• A new dryer must be installed.

• The system must be evacuated and properly changed.

Note: The moisture indicator reading is most efficient after the air conditioning system has been in operation 3 hours or more. For the best results, have the operator inspect the moisture indicator at lunch time and at the end of each shift.

Note: Moisture indicators have been removed from most of the systems since 1999 because of the inaccuracy of the color change and misinterpretation of the color meaning by service personnel.