Part 2 of 2

A/C EVAPORATOR
The evaporator coil is located in the HVAC housing, under the instrument panel. The evaporator coil is positioned in the HVAC housing so that all air that enters the housing must pass over the fins of the evaporator before it is distributed through the system ducts and outlets. However, air passing over the evaporator coil fins will only be conditioned when the compressor is engaged and circulating refrigerant through the evaporator coil tubes.

Refrigerant enters the evaporator from the orifice tube as a low-temperature, low-pressure liquid. As air flows over the fins of the evaporator, the humidity in the air condenses on the fins, and the heat from the air is absorbed by the refrigerant. Heat absorption causes the refrigerant to boil and vaporize. The refrigerant becomes a low-pressure gas before it leaves the evaporator.

The evaporator coil cannot be repaired and, if faulty or damaged, it must be replaced.

HEATER CORE
The heater core is located in the HVAC housing, under the instrument panel. It is a heat exchanger made of rows of tubes and fins.

Engine coolant is circulated through heater hoses to the heater core at all times. As the coolant flows through the heater core, heat removed from the engine is transferred to the heater core fins and tubes. Air directed through the heater core picks up the heat from the heater core fins. The temperature control door allows control of the heater output air temperature by controlling how much of the air flowing through the HVAC housing is directed through the heater core. The blower motor speed controls the volume of air flowing through the HVAC housing.

The heater core cannot be repaired and, if faulty or damaged, it must be replaced. Refer to Cooling for more information on the engine cooling system, the engine coolant and the heater hoses.

RECEIVER / DRIER
The receiver/drier is mounted in the engine compartment between the condenser and is part of the liquid line assembly. The filter/drier cannot be repaired, if the filter/drier is faulty damaged, left open to the atmosphere or contaminated the line assembly must be replaced.

The filter-drier performs a filtering action to prevent foreign material in the refrigerant from contaminating the expansion valve. A desiccant bag is mounted inside the filter-drier canister to absorb any moisture which may have metered and become trapped within the refrigerant system. In addition, during periods of high demand air conditioner operation, the filter-drier acts as a reservoir to store surplus refrigerant. Refrigerant enters the filter-drier as a high-pressure, low-temperature liquid.

REFRIGERANT
The refrigerant used in this air conditioning system is a HydroFluoroCarbon (HFC), type R-134a. Unlike R-12, which is a ChloroFluoroCarbon (CFC), R-134a refrigerant does not contain ozone-depleting chlorine. R-134a refrigerant is a non-toxic, non-flammable, clear, and colorless liquefied gas.

Even though R-134a does not contain chlorine, it must be reclaimed and recycled just like CFC-type refrigerants. This is because R-134a is a greenhouse gas and can contribute to global warming.

R-134a refrigerant is not compatible with R-12 refrigerant in an air conditioning system. Even a small amount of R-12 added to an R-134a refrigerant system will cause compressor failure, refrigerant oil sludge or poor air conditioning system performance. In addition, the PolyAlkylene Glycol (PAG) synthetic refrigerant oils used in an R-134a refrigerant system are not compatible with the mineral-based refrigerant oils used in an R-12 refrigerant system.

R-134a refrigerant system service ports, service tool couplers and refrigerant dispensing bottles have all been designed with unique fittings to ensure that an R-134a system is not accidentally contaminated with the wrong refrigerant (R-12). There are also labels posted in the engine compartment of the vehicle and on the compressor identifying to service technicians that the air conditioning system is equipped with R-134a.

REFRIGERANT OIL
The refrigerant oil used in R-134a refrigerant systems is a synthetic-based, PolyAlkylene Glycol (PAG), wax-free lubricant. Mineral-based R-12 refrigerant oils are not compatible with PAG oils, and should never be introduced to an R-134a refrigerant system.

There are different PAG oils available, and each contains a different additive package. The 10PA17 compressor used in this vehicle is designed to use an ND8 PAG refrigerant oil. Use only refrigerant oil of this same type to service the refrigerant system.

After performing any refrigerant recovery or recycling operation, always replenish the refrigerant system with the same amount of the recommended refrigerant oil as was removed. Too little refrigerant oil can cause compressor damage, and too much can reduce air conditioning system performance.

PAG refrigerant oil is much more hygroscopic than mineral oil, and will absorb any moisture it comes into contact with, even moisture in the air. The PAG oil container should always be kept tightly capped until it is ready to be used. After use, recap the oil container immediately to prevent moisture contamination.

REFRIGERANT SYSTEM SERVICE PORT
The two refrigerant system service ports are used to charge, recover/recycle, evacuate, and test the air conditioning refrigerant system. Unique service port coupler sizes are used on the R-134a system to ensure that the refrigerant system is not accidentally contaminated by the use of the wrong refrigerant (R-12), or refrigerant system service equipment.

The high pressure service port is located on the liquid line near the receiver/drier. The low pressure service port is located on the suction line near the evaporator at the rear of the engine compartment.

Each of the service ports has a threaded plastic protective cap installed over it from the factory. After servicing the refrigerant system, always reinstall both of the service port caps.

VISCOUS HEATER

Viscous Heater
The diesel engine has an engine mounted mechanical device called a Viscous Heater that is used to heat the coolant coming from the engine to the heater core. The Viscous Heater is driven by the engine fan belt and has a electro-mechanical clutch which is controlled by the HVAC control unit.

The Viscous Heater is driven by the engine fan belt. The Viscous Heater has an electro-mechanical clutch that receives a signal from the HVAC control head and the Viscous Heater controller that energizes and engages the clutch. Once engaged the clutch allows the Viscous Heater to increase the temperature of the coolant flowing to the heater core, which provides heat the passenger compartment quicker than normal engines without the Viscous Heater. The Viscous Heater generates heat by means of friction which heats a special Silicon Oil within its housing which is then transferred to the engine coolant when the coolant passes over fins within the pump. Please note that the coolant is isolated from the silicon oil within the pump housing. When demand for passenger compartment heat decreases the Viscous Heater clutch will receive an input from the Viscous heater controller to disengage.

Fig.17 Clutch Assembly - Typical:

Viscous Heater Clutch
The basic viscous heater clutch assembly consists of a stationary electromagnetic coil, a hub bearing and pulley assembly and a clutch plate. The electromagnetic coil unit and the hub bearing and pulley assembly are each retained on the nose of the compressor front housing with snap rings. The clutch plate is keyed to the viscous heater shaft and secured with a nut. These components provide the means to engage and disengage the viscous heater from the engine accessory drive belt.

When the clutch coil is energized, it magnetically draws the clutch into contact with the pulley and drives the viscous heater shaft. When the coil is not energized the pulley freewheels on the clutch hub bearing, which is part of the pulley. The viscous heater clutch and coil are the only serviced parts on the viscous heater assembly. If the viscous heater is inoperative or damaged the entire assembly must be replaced. The viscous heater clutch engagement is controlled by several components: the viscous heater controller, the engine powertrain control module and the HVAC control head.