TYPES OF
AUTO AIR CONDITIONING
SYSTEMS
Fix Orifice Tube and Expansion Valve
Systems
Fix Orifice Tube System
Stage 1: Compressor
● The compressor draws the cold low pressure refrigerant vapor from the
evaporator.
● Compresses it into high pressure refrigerant vapor.
● Increased pressure also greatly increases refrigerant temperature.
● Pushes the refrigerant into the condenser.
Fix Orifice Tube System
Stage 2: Condenser
● The high temperature, high pressure refrigerant enters the top tap of the
condenser.
● The heat absorbed by refrigerant, being greater than the aluminum that the
condenser is made of flows through the tubes and the fins, where it dissipates on
to the atmosphere.
● The refrigerant temperature at the bottom of the condenser is now significantly
lower than at the top, this drop of temperature condenses the refrigerant into a
high pressure liquid refrigerant. (phase change)
● A fan continuously blows air through the condenser fins, ensuring refrigerant
heat is dissipated on to the atmosphere regardless if the vehicle is moving or
stationary.
Fix Orifice Tube System
Stage 3: Fix Orifice Tube
● A fix orifice tube is a tube with no moving parts. It has a small diameter tube
which restricts the flow of liquid refrigerant. Diameter is determined by
system design.
● Separates the high pressure side and low pressure side of the Air
conditioning system. The liquid refrigerant boils and evaporates once they
reach the evaporators low pressure area.
Fix Orifice Tube System
Stage 4: Evaporator
● Liquid refrigerant starts to boil and evaporate once it reaches the
evaporator.
● The sudden drop in pressure also causes a sudden drop in temperature.
● The extremely low temperature of the refrigerant allows it to absorb a lot
more heat energy from the cabin air being blown through it by fans.
● The fins and the tubes trap heat energy from the cabin air, then transfers
them to the refrigerant. Resulting in cold air circulating inside the cars
cabin.
● Refrigerant leaves the evaporator in a vapor state and flows to the
accumulator.
Fix Orifice Tube System
Stage 5: Accumulator
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Low pressure vapor refrigerant is sucked to the bottom of the accumulator.
Before reaching the bottom, the refrigerant passes through desiccant bags sandwiched by two
filter pads.
The desiccant absorbs moisture from the refrigerant.
Any further moisture drops to the bottom of the accumulator and remains there until it
evaporates fully.
Vapor which is lighter than liquid refrigerant rises to the top of the accumulator, where the outlet
line is located.
The compressor then sucks the vapor through the accumulator outlet line and the refrigeration
cycles starts all over again.
Note: An AC clutch sensor is mostly located in the accumulator. It senses the pressure in the evaporator
line, switches the compressor clutch on or off to maintain the refrigerant flow rate required. An
excessive flow rate may cause freezing in the evaporator, clogging up the system.
Expansion Valve System
Stage 1: Compressor
● The compressor draws the cold low pressure refrigerant vapor from the
evaporator.
● Compresses it into high pressure refrigerant vapor.
● Increased pressure also greatly increases refrigerant temperature.
● Pushes the refrigerant into the condenser.
Note: The expansion valve regulates refrigerant flow by measuring the
refrigerant temperature that is leaving the evaporator.
Expansion Valve System
Stage 2: Condenser
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The high temperature, high pressure refrigerant enters the top tap of the condenser.
The heat absorbed by refrigerant, being greater than the aluminum that the condenser is
made of flows through the tubes and the fins, where it dissipates on to the atmosphere.
The refrigerant temperature at the bottom of the condenser is now significantly lower than
at the top, this drop of temperature condenses the refrigerant into a high pressure liquid
refrigerant. (phase change)
A fan continuously blows air through the condenser fins, ensuring refrigerant heat is
dissipated on to the atmosphere regardless if the vehicle is moving or stationary.
Expansion Valve System
Stage 3: Receiver Drier
● The high pressure refrigerant is forced through desiccant and filters.
● Pollutants are removed and the refrigerant is dried.
● It also stores liquid refrigerant at the bottom of the container.
Expansion Valve System
Stage 4: Expansion Valve
● Receives the filtered high pressure liquid refrigerant.
● De-pressurizes the liquid refrigerant before entering the evaporator.
● Refrigerant immediately boils and turns to vapor.
Types of Compressors
Stage 5: Evaporator
● Liquid refrigerant starts to boil and evaporate once it reaches the evaporator.
● The sudden drop in pressure also causes a sudden drop in temperature.
● The extremely low temperature of the refrigerant allows it to absorb a lot more
heat energy from the cabin air being blown through it by fans.
● The fins and the tubes trap heat energy from the cabin air, then transfers them
to the refrigerant. Resulting in cold air circulating inside the cars cabin.
● Refrigerant leaves the evaporator in a vapor state and flows to the accumulator.