Automotive Air Conditioning

• Automotive air-conditioning systems must manage to cool air, circulate it, purify it, and dehumidify it inside the vehicle to provide comfort.

Understanding Heat

• Heat transfer is the movement of energy from a warmer substance to a cooler one.
• Absolute Zero (-273°C) represents the point where all heat is removed from an object.
• An average person is most comfortable in a temperature and humidity range of 21°C to 26°C, with a relative humidity of 45 to 50%.
• Heat quantity is measured in Kilocalories (KCALs); raising one kilogram of water one degree Celsius requires one KCAL.

Changes of State

• Evaporation occurs when enough heat is added to a liquid to turn it into a vapor or gas.
• Condensation is the opposite of evaporation, where a vapor cools and becomes a liquid.
• Freezing is the change of state where heat is removed from a liquid until it becomes a solid and must be avoided to prevent damage.

Pressure & Temperature Relationship

• Increasing pressure raises boiling points, while decreasing pressure lowers them
• A 110 kPa radiator cap raises the coolant temperature to 126°C before boiling.

The Ozone Layer

• Ozone (O3) in the stratosphere acts as a shield against harmful ultraviolet radiation.
• CFCs containing chlorine deplete the ozone layer, leading to skin cancer, eye cataracts, impaired immunity, and damage to crops and aquatic life.

R134a Properties

• Automotive industry shifted to HFC 134a (Tetra Fluoroethane) in 1993 as a non-ozone-depleting refrigerant.
• R134a and water have the same abilities to change the state, but R134a can do this more rapidly and at much lower temperature than water.
• Above -26.3°C, R134a vaporizes, absorbing heat and creating a cooling effect.
• R134a is stored under high pressure.

System Types

• Expansion block valve system, parallel flow condenser system, orifice tube system, and expansion valve dual system are system types.

Principles of Air Conditioning (Expansion Valve System)

• R134a vapor under low pressure becomes high-pressure via the compressor, circulates to the condenser with lubricant oil, and releases heat, turning into a high-pressure/temperature liquid.
• This liquid travels to the expansion valve through a filter, where a small orifice restricts flow.
• Suction moves the R134a via the TX valve to the system's low-pressure side, where it absorbs heat and turns into a low-pressure vapor for the compressor.

Components - Compressors

• Compressors like piston, scroll, wobble plate, variable stroke, or vane types are used in automotive A/C systems.
• "A reciprocating piston, fixed displacement compressor", pistons are operated by a wobble plate, which moves them backwards and forwards in the cylinders.

Components - Receiver Drier

• Filter drier acts as a particle filter, refrigerant storage container, and moisture absorber as well as the silica gel beads (desiccant) absorb small quantities of moisture.
• R134a filter dryers have NO sight glass because at approximately 700C refrigerant temperature the PAG oil will foam.
• The connection indicated with "IN" goes to the condenser outlet.

Components - Super Heat

• The value of super heat is the temperature difference above the point at which R134a turns into a vapor. The thermal expansion valve (TXV) values are preset at factory to compensate for it.
• There is condensation which results from moisture that's inside the warm air which condenses on the outer evaporator after it's surface temperature has been lowered to below than the due point temperature.

O-Rings

• Hydrogenated nitrile butadiene rubber (HNBR) identifies the "O" ring rubber compound used for R134a.
• R12 "O" rings are coloured black and should NOTbe used with R134a as the “O” ring will be damaged.
• R134a “O” rings can be used with an R12 system.

Hoses

• Refrigerant hose will incorporate a nylon inner lining in order to reduce the normal leakage due to the smaller molecular size and higher operating pressures of R134a.
• You should never use a R12 hose (unless of a barrier type) in an R134a A/C system since the the PAG oil and hydrogen will cause the normal R12 nitrile hoses to deteriorate.

Charging Ports

• Charging ports are fitted onto components such as hoses, tubes and filter dryers receivers that enable the AC to be tested.
• Shradervalves designed for R134a must only be used in R134a systems due to the seal material.

Wiring A/C System

• The pressure switches are connected in series with the compressor clutch. If an "under" or "over" system pressure occurs, the pressure switch will "open circuit".
• The ELECTRONIC CONTROL MODULE (ECM) is interconnected into the A/C wiring circuit on electronic fuel injected vehicles.

Retrofitting frim R12 to R134a

• Majority of automotive manufacturers recommending PAG (Poly Alkaline Glycol) oil as the only oil replacement when retrofitting R12 since Ariazone also recommends POA oil which is fully synthetic oil and suitable with all compressors refrigerant R12 and R134a.
• Don't retrofit functioning R12 A/C systems with no refrigerant leaks unless necessary like replacing a compressor, R12 is unavailable, or accident damage.

Refrigerant Safety

• Always wear protective eyewear and gloves due to R134a having a low boiling point in order to not cause frostbite or eye injuries.
• Provide adequate ventilation as it's heaver than air and prevent the thermal expansion of the refrigerant contained in the system by using care when hot water steam cleaning the engine.

Leak Detection & Detectors

• As refrigerant leaks can lead to system damage, it's vital to find and fix them as air and moisture can corrode internal components and must be rectified.
• Leaks cause a refrigerant circulation of the compressor which then helps cool the compressor to be dependent on, and it depends on the compressor lubrication.