M312, M315, M318 and M320 Excavators Air Conditioning and Heating Caterpillar


Air Conditioning System

Usage:

M318 6ES



Illustration 1g00296445

(1) Pulley (engine driven component)

(2) Compressor

(3) Hose (high pressure)

(4) Hose (low pressure)

(5) Condenser

(6) Accumulator (dryer)

(7) Expansion valve

(8) Heater/Air conditioner unit

(9) Air outlet that is located under the seat

(10) Access panel that is located behind the cab

(11) Hose (inlet to expansion valve)

(12) Hose (outlet from evaporator)

The air conditioning system is a closed circuit that uses refrigerant under pressure to cool the surrounding air. This expansion valve system includes the following five components: compressor (2), condenser (5), accumulator (dryer) (6), expansion valve (7) and the evaporator.

Compressor

The flow of refrigerant in the air conditioning system begins at compressor (2). The compressor circulates the refrigerant through the system. Refrigerant at a low pressure enters the compressor. Refrigerant at a high pressure leaves the compressor. The refrigerant that leaves the compressor is at a high temperature due to the increase in energy from compression.

Condenser

The refrigerant flows from the compressor to condenser (5). The condenser coils remove the latent heat from the refrigerant. Air that passes over the coils removes the latent heat from the system. An electric fan provides the cooling air. As the refrigerant gives up the latent heat, the refrigerant condenses to a high pressure liquid.

Accumulator (dryer)

The condensed refrigerant is collected in accumulator (6). During times of no operation, the accumulator serves as a storage tank for the liquid refrigerant. The lower half of the accumulator is a dryer that is a solid filter. Contaminants and moisture is removed from the refrigerant in the dryer. By cleaning and refining the refrigerant, the system lasts longer.

Expansion Valve

During operation, the refrigerant from the accumulator flows to expansion valve (7). The expansion valve is a needle valve that controls the flow of refrigerant into the evaporator. The outlet from the evaporator is located in the upper portion of the expansion valve. The inlet to the evaporator is located in the lower portion of the expansion valve. A diaphragm is located at the top of the valve. Some of the refrigerant vapor that leaves the evaporator enters the area under the diaphragm. As the temperature of the refrigerant vapor that leaves the evaporator increases, the pressure under the diaphragm increases. The increase in pressure pushes up on the diaphragm in the expansion valve. The diaphragm opens the needle valve. The open valve allows more refrigerant to flow to the evaporator. When the temperature of the refrigerant that leaves the evaporator lowers, the pressure under the diaphragm is reduced. The lower pressure under the diaphragm allows the diaphragm to move down. The diaphragm closes the inlet to the expansion valve. The closed expansion valve restricts the flow of refrigerant to the evaporator. As the refrigerant flows through the expansion valve, the refrigerant expands. The pressure of the refrigerant is reduced because of the expansion.

Evaporator

The refrigerant flows through the restricted needle valve of the expansion valve to the evaporator. The refrigerant flows through the lower portion of the expansion valve. The evaporator is a heat exchanger. The surrounding air passes over the evaporator coils. The liquid refrigerant enters the evaporator and the refrigerant absorbs the latent heat of the air. Fins are placed on the evaporator coils in order to increase the surface area. The heat transfer of the evaporator is increased by the surface area. The refrigerant picks up the latent heat from the air, and the refrigerant begins to evaporate. As the temperature of the refrigerant increases, the temperature of the air decreases. The refrigerant flashes into a vapor before the refrigerant leaves the evaporator. The refrigerant vapor flows from the evaporator to the compressor. The refrigerant leaves the evaporator through the upper portion of the expansion valve. Only vapor should flow to the compressor. Liquid refrigerant can damage the compressor.

Heater Core

A heater core is placed before the evaporator in the heater/air conditioner unit. The heater core is separate from the air conditioning circuit. The heater core uses coolant from the engine to heat the air.

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