What are the types of car air conditioning?
Air conditioning is a commonly used car feature in the hot Australian climate. Many cars come with factory fitted air-conditioning while others are fitted as after-market extras.
Understanding which types of air conditioners are available and how they work can help you make an informed decision about the best air conditioning for you.
The general function of air conditioners
The basic principle of an air conditioner is the removal of heat from the air inside the vehicle using a refrigerant.
The most common refrigerant in use today is R-134a. This is a hydrofluorocarbon product, which is less harmful to the ozone layer than older chlorofluorocarbon products like freon. Every car air conditioner has a compressor which increases the pressure of the refrigerant gas. At the same time, the temperature of the refrigerant also increases.
- The compressed gas flows to a condenser where it is converted into a liquid at a high temperature and pressure.
- The refrigerant liquid passes through either an orifice tube or a thermostatic expansion valve (TXV), where the temperature drops significantly before passing into an evaporator.
- The refrigerant converts from liquid back to gas, removing heat from the evaporator and the internal vehicle air blowing over it.
The cycle completes as the compressor takes suction from the evaporator, and the process begins again.
What are the two types of car air conditioner?
Car air conditioners have either an orifice tube or a thermostatic expansion valve. The function of each is the same – to allow the liquid refrigerant to expand and thus drop its temperature in preparation for evaporation. However, they work in slightly different ways:
Orifice tubes have a fixed opening creating the pressure drop as the liquid flows through it. In other words, the orifice tube has no way to regulate the flow of refrigerant through it.
However, flow rate is very important because when the flow is too low, the refrigerant may freeze in the evaporator causing blockages. If the flow is too high, then liquid may carry through into the compressor causing it to fail.
Vehicles with an orifice tube installed regulate the flow of refrigerant by switching the compressor on and off or using a variable output compressor.
TXVs can regulate the flow of refrigerant by opening or closing the valve. A wider opening allows a higher flow and a lower pressure drop, while a narrower opening restricts the flow and causes a higher pressure drop across the valve.
The valve opens and closes automatically based on the temperature at the evaporator outlet. The air conditioner is therefore controlled by the TXV rather than by the compressor switching on and off.
Pros and cons of the two types of air conditioner
- Pros: They are simpler than valves because they have no moving parts.
- Cons: They can pick up debris that passes through from the compressor or condenser. This would cause a blockage in the system and affect the compressor performance.
- Pros: They have the advantage of not cycling the compressor continuously and therefore have a reduced wear and tear.
- Cons: They have moving parts and so the valve itself could fail even if the rest of the air conditioner system was working normally.
Can you replace an orifice tube with a TXV
The air conditioning system setup for an orifice tube is slightly different than that for a TXV. You cannot change the one out for the other without also making other changes to the system.
For example, the orifice tube installation has an accumulator downstream of the evaporator. This traps any liquid refrigerant before it reaches the compressor.
On the other hand, a TXV system has a receiver/dryer on the outlet of the condenser.
Repairing or replacing your air conditioning system
There are a number of potential causes for an air conditioner to lose its effectiveness.
- A low system pressure
- A compressor failure
- A blockage in the system
It is advisable to take your vehicle to an air conditioning specialist for correct diagnosis and repair.
Contact us for all your air conditioner diagnosis and repair needs.