Refrigeration System
Compressor
The Saturn compressor is a variable displacement rotary vane type pump. The rotor assembly houses five lightweight vanes that extend outward contacting the cylinder wall creating the compression area. The compressor has an internal control valve that allows it to change its pumping capacity or displacement, reacting to heat loads on the air conditioning system. The range of displacement can vary from 5 percent (5.5 cc) to 100 percent (110 cc). The compressor's natural or resting state is at minimum displacement.
The compressor performs two main functions. It compresses the low pressure refrigerant vapor from the evaporator into a high pressure high temperature vapor, and pumps compressor oil through the A/C system.
Compressor Clutch
The magnetic clutch transmits the engine power to the compressor when the A/C button is depressed. The clutch assembly consists of a drive plate, pulley and field coil. The drive plate is splined to the compressor shaft. The pulley and bearing assembly is pressed on the compressor hub, and the field coil is mounted to the compressor body. When current flows through the field coil, the drive plate is pulled into the pulley by electromagnetic force.
When the field coil is not energized the drive plate separates from the pulley and the compressor stops. A diode is used to protect electrical circuits from voltage spikes. The diode is located in the underhood junction block.
Pressure Relief Valve
Mounted in the front head is a high pressure relief valve. To protect the A/C system from high pressure in the event of an electrical control system failure the valve will begin to open at about 3654 kPa (530 psi). As system pressure is reduced the valve will reseat at about 2930 (425 psi). If the valve ever opens it must be replaced.
Thermal Expansion Valve (TXV)
Thermal Expansion Valve (TXV):
The thermal expansion valve is installed on the evaporator inlet and outlet pipes. The expansion valve converts the high-pressure liquid refrigerant from the receiver drier to a low-pressure liquid refrigerant by forcing it through a small port before entering the evaporator.
When the heat load increases or decreases, the expansion valve will supply the correct quantity of refrigerant to the evaporator for maximum heat transfer.
The expansion valve consists of the block and body.
The body includes a temperature sensor for sensing the temperature of vapor. A diaphragm transmits changes in pressure inside the temperature sensor bulb stem which is connected to the diaphragm.
The stem is tapered and moves in response to changes in the pressure inside the temperature sensor bulb. This controls the flow of refrigerant by changing the size of the valve opening.
The body has an equalizing pressure port through which the vapor pressure of the evaporator acts on the bottom of the diaphragm.
When the evaporator heat load increases, the stem is pushed down and the flow of refrigerant to the evaporator increases. As a result, the vapor pressure and temperature of the refrigerant on the evaporator outlet side changes. When the evaporator heat load decreases, the situation is reversed.
Receiver-Dehydrator
Connected to the condenser assembly outlet pipe, the scaled receiver-dehydrator assembly acts as a refrigerant storage container receiving R-134a liquid.
At the center of the receiver-dehydrator is the desiccant which acts as a drying agent for moisture that may have entered the system. The filter and baffle on the upper end of the component is for retaining the desiccant bags and removing contamination from the A/C system.
Condenser
The condenser assembly in front of the radiator is made up of coils which carry refrigerant, and cooling fins to provide rapid transfer of heat. The air passing through the condenser cools the high pressure refrigerant vapor causing it to condense into a liquid.
The condenser is made of aluminum tubes on which are mounted aluminum fins.
The fins provide the cooling capacity of the condenser and should be kept clean and should not be bent or otherwise damaged.
IMPORTANT: All models are serviced with the "header type" condenser.
Temperature and Mode Cables?
The operation of the A/C system is controlled by the buttons, rotary switch, and levers on the HVAC control. The compressor clutch and recirc motor are controlled electrically by push buttons on the control head.
Blower speeds are controlled in all modes by a five position rotary switch. The blower, compressor, and recirc motor are not operational when the blower switch is in the Off position.
The temperature lever controls the temperature door through a cable from the HVAC control assembly to the HVAC module. The mode lever controls the various mode positions by a cable from the HVAC control to the HVAC module.
HVAC Module
The HVAC module consists of the recirc motor, the blower motor and fan, the blower motor resistor, the heater core, and the evaporator core. The operations of these assemblies are controlled by the levers and switches on the HVAC control panel.
Distribution of the air is controlled by the mode levers and buttons on the control assembly. The various positions of the mode levers and buttons direct cooled, heated, blended, outside, or inside air through the air ducts. The flow of air during the various modes of operations is as follows:
^ Face - Instrument Panel Outlets With a Small Amount of Bleed Air to the Heater
^ Face and Feet - Instrument Panel Outlets, and Floor Outlets
^ Feet - Floor Outlets With a Small Amount of Bleed Air to Defroster
^ Top - Defroster Ducts With a Small Amount of Bleed Air to the Heater
Evaporator Core
The evaporator is a device which cools and dehumidifies the air before it enters the passenger compartment. Low pressure liquid refrigerant flows through the expansion valve into evaporator. The heat in the air passing through the evaporator core is lost to the cooler surface of the core, thereby cooling the air. As the process of heat loss from the air to the evaporator core surface is taking place, the moisture (humidity) in the air condenses on the outside surface of the evaporator core and is drained off as water. Evaporator pipes are now wrapped with mastic for system noise reduction.
Heater Core
The heater core heats the air before it enters the passenger compartment. Engine coolant is circulated through the core to heat the air passing over the fins of the core.
The core is functional at all times (no water valve) and may be used to temper air in A/C mode as well as heat, vent, bi-level, and defrost.
Recirc Motor
The recirc motor rotates the valve between inside and outside air. When recirc is activated, the motor allows the air inside the passenger compartment to be drawn back into the HVAC module.
Some outside air is also drawn in. When recirc is not activated fresh outside air is drawn into the system.
Blower Motor
The blower motor is a permanent magnet motor with a squirrel cage fan. Its purpose is to provide air flow to the passenger compartment. The blower speeds are controlled in all modes by a five position rotary switch.
The blower motor and fan is a balanced assembly. Weights could be visible on the fan cage.
All vehicles have a blower motor cover to reduce motor noise.
Blower Motor Resistor
The blower motor resistor is in series to the blower motor. Its purpose is to control the speed (or RPM) of the blower. The resistors allow for the selection of blower speeds, LO, M1 and M2.