Refrigeration System
Caution: Avoid breathing the A/C Refrigerant 134a (R-134a) and the lubricant vapor or the mist. Exposure may irritate the eyes, nose, and throat. Work in a well ventilated area. In order to remove R-134a from the A/C system, use service equipment that is certified to meet the requirements of SAE J 2210 (R-134a recycling equipment). If an accidental system discharge occurs, ventilate the work area before continuing service. Additional health and safety information may be obtained from the refrigerant and lubricant manufacturers.Refrigerant performs the following functions in the air conditioning system:
^ Absorbs heat
^ Carries heat
^ Releases heat
These vehicles use Refrigerant-134a (R-134a). Refrigerant-134a is a nontoxic, nonflammable, clear, colorless liquefied gas.
Thermal Expansion Valve Description
The expansion valve regulates the flow of liquid refrigerant into the core of the evaporator. As the condensed liquid refrigerant is released through the expansion valve, the refrigerant pressure decreases considerably. As the pressure drops, the refrigerant temperature drops. The refrigerant passing through the expansion valve transforms from a high-pressure, medium-temperature liquid into a low-pressure, low-temperature liquid.
Evaporator Description
The evaporator cools and dehumidifies air before the air enters the passenger compartment. The following events occur in the evaporator:
1. Low-pressure, low temperature liquid/vapor refrigerant enters the evaporator.
2. The refrigerant flows through the evaporator's tubing.
3. The refrigerant evaporates.
4. The refrigerant exits the evaporator as low-pressure, low temperature, mostly vapor refrigerant.
5. As the refrigerant evaporates, the refrigerant absorbs heat from the air flowing over the evaporator.
As the process of heat loss from the air to the evaporator core is taking place, any moisture (humidity) in the air condenses on the outside surface of the evaporator core and the moisture drains off as water.
Condenser Description
The condenser receives high pressure, high temperature refrigerant vapor from the A/C compressor. The condenser is made up of aluminum tubing and cooling fins which allow rapid heat transfer away from the high-pressure, high temperature refrigerant vapor. The cooling fins cause the high pressure, high temperature refrigerant vapor to condense into a high-pressure, medium temperature liquid.
Condenser Fan Description
The condenser fan is crucial to the proper operation of the air conditioning (A/C) system. The fan ensures a sufficient amount of airflow across the condenser throughout the vehicle's operating range. Inspect the fan during all A/C diagnostic procedures. Give particular attention to the fan whenever excessive high-side pressure is encountered.
Heater Core Description
The heater core is the main component of the heater system. The heater core is located inside of the heater and evaporator module. Engine coolant is pumped into the heater core from the engine whenever the engine is operating. The heater core fins transfers the heat from the engine coolant to the air passing over the heater core. The heater core has specific inlet and outlet tubes. The placement of the heater hoses should be noted prior to servicing the heater core or the heater hoses. The temperature control is linked to the temperature valve by a flexible control cable. When you rotate temperature control counterclockwise to the full COLD position, the temperature valve is held snugly against the air entrance to the heater core. The following actions occur:
^ All of the airflow from the evaporator bypasses the heater core.
^ No heat transfer occurs.
When you turn the temperature control away from the full COLD position, the temperature valve begins to direct air to the heater core. This action allows air to flow through the heater core. The farther the temperature control is rotated clockwise, the more the temperature valve directs air through the heater core. The air discharge is warmer when most of the airflow is heated in this manner. The air discharge is warmer because the heated and unheated air flows join and mix together thoroughly beyond the heater core.
When you rotate the temperature lever clockwise to the full HOT position, the temperature valve blocks off the passage that allows air to bypass the heater core. This action causes passage of the airflow through the heater core.
Receiver Dehydrator Description
The receiver/dryer is mounted to the front of the condenser. The receiver/dryer is connected to the condenser outlet pipe (1) between the condenser and the evaporator.
The receiver/dryer performs the following functions:
^ The receiver/dryer serves as a temporary storage container for condensed liquid refrigerant.
^ The receiver/dryer acts as a filter which removes moisture and contaminants from the system.
Service Port and Cap Description
The primary seal for the service ports is the sealing cap. The cap contains a specially designed O-ring or gasket. The O-ring or gasket provides a leak-free seal. Loss of the refrigerant charge will occur if
any of the following conditions occur:
^ The cap becomes loose
^ The cap is missing
^ The wrong cap is used Ensure that the cap has a rubber seal.
Compressor Description
The air conditioning (A/C) system compressor is driven by a belt from the engine crankshaft through the compressor clutch pulley.
The compressor pulley rotates freely, without turning the compressor drive shaft until an electromagnetic clutch coil is energized. When voltage is applied in order to energize the clutch coil, the pressure plate is drawn rearward toward the pulley. The magnetic field locks the pressure plate and the pulley together as 1 unit in order to rotate the compressor drive shaft. The A/C compressor performs 2 main functions:
^ The compressor compresses low pressure refrigerant vapor from the evaporator into a high pressure, high temperature vapor.
^ The compressor pumps the refrigerant and the refrigerant oil throughout the A/C system.
The clutch coil is energized by the A/C compressor control module.
The following compressor components can be replaced:
^ The clutch coil
^ The clutch pulley
^ The drive shaft seal
^ The pressure plate
^ The pressure relief valve
Replace the compressor as a unit if any internal part of the compressor assembly malfunctions or wears out.
A/C Compressor Control Module Description
The air conditioning (A/C) compressor control module controls the operation of the compressor clutch in response to the signals received from the following components:
^ The A/C ON/OFF switch
^ The A/C refrigerant pressure switch
^ The refrigerant (evaporator) temperature sensor
^ The powertrain control module (PCM)
With the A/C system in operation the A/C compressor control module performs the following functions:
^ Energizes the compressor clutch in response to the following conditions:
- An A/C system ON request
- The determination of favorable system conditions for A/C operation
^ De-energizes the compressor clutch in response to the following conditions:
- A high refrigerant pressure signal from the A/C refrigerant pressure switch
- A low refrigerant pressure signal from the A/C refrigerant pressure switch
- A low evaporator temperature signal from the refrigerant (evaporator) temperature sensor
- A high engine demand signal from the PCM
- An A/C system OFF request
O-Ring/Flat Washer Description
Install new approved service replacement air conditioning O-ring(s) and flat washers whenever a joint or fitting is disassembled.
Some vehicles use flat sealing washers and O-ring(s) to seal the refrigerant system. The flat washers are used on block fittings of refrigerant components. The O-ring(s) is used to seal the refrigerant tubes. The O-ring fitting consists of:
^ An aluminum alloy, externally threaded fitting which is welded to an aluminum tube.
^ A free-spinning internally threaded nut.
^ An aluminum tube end which accommodates the O-ring(s).
Verify that the flat washers or O-ring(s) have not been damaged prior to installation. Replace damaged parts. Coat O-ring(s) and flat washers with the approved refrigerant oil.
Failure to use the proper service replacement parts and procedures may result in a leak.
Service Caps Seal
The primary seal for the service ports is the sealing cap. The cap contains a specially designed O-ring or gasket which provides a leak free seal. Should the cap be loose, missing, or the wrong usage, a loss of refrigerant could result.