DENSO: the real A/C Specialists
Almost all modern cars are equipped with air-conditioning (A/C), either manual or automatic controlled, representing a real opportunity for workshops to offer competent air-conditioning maintenance and repair.
There is a common misconception that buying a relatively inexpensive automatic charging station is all you need to provide a good service at a low cost.
How do air-conditioning systems work?
Vehicle air-conditioning is designed to provide a comfortable environment for the driver and passengers whatever the weather. The most significant factors for comfort are temperature, humidity, airflow, radiant heat and clean air.
All car air-conditioners use a ‘vapour compression’ refrigeration system using a refrigerant to exchange high quantities of heat from the air blown into the car; cooling, heating and dehumidifying the car’s interior.
The refrigerant cycle consists of four main components: an evaporator, a compressor, a condenser and an expansion device. Two of these increase and decrease pressure and temperature, and two dissipate heat.
Receiver dryer or accumulator tank
Depending on the A/C system’s design it either has a receiver dryer or accumulator tank. Systems with a thermal expansion valve or TXV have the receiver dryer installed after the condenser, and systems with orifice tube (fixed restrictor) have the accumulator tank installed after the evaporator. Their functions are generally the same except that the receiver dryer separates gas and the accumulator tank separates liquid.
Other functions are storage of refrigerant, filtration and drying. It can be necessary to make replacements after a certain period of time. Always replace the receiver dryer or accumulator tank when the system has either been empty or has been opened - even if it was only opened to replace a simple o-ring. This is because the internal drying material, which is designed for one-time-only installation, will be saturated with water following exposure for the second time to the outside air.
A comfortable environment
Different sensors are used to control the air-conditioner. When a vehicle is equipped with automatic air-conditioning, ‘climate control’ temperature sensors, combined with humidity and solar radiation sensors, maintain a comfortable environment.
Regular maintenance is key
To minimise the risk of system failure and expensive repair, year-round operation and annual maintenance are important. The most common failures include:
- Insufficient refrigerant. This results in poor cooling performance and compressor seizure due to poor lubrication. Main causes are a long period of air-conditioning switch of time (only summer use) and leakage of condenser or hose/ tube
- Wrong oil or wrong UV leak dye leading to poor lubrication of the compressor and/or clogging of expansion valve or orifice tube. This is caused to mixing of wrong oils
- Insufficient cleaning of the refrigerant cycle after compressor seizure. Compressor failure means more parts need replacement and others need extensive flushing. Not doing so increases risk of repeated compressor failure until the necessary measures are taken
- Liquid lock, which results in compressor seizure or noise. This is mainly caused by a) too much compressor oil and b) charging a liquid refrigerant to the low pressure side
- An extended maintenance schedule or no maintenance of the refrigerant charging equipment. This will result in compressor seizure and expansion valve blockage
- Insufficient heat transfer at the condenser resulting in high thermal stress of the compressor leading to compressor seizure. The cause is either lack of maintenance and dirt accumulation between condenser and radiator or a broken condenser ventilator
- Breaking of DL-pulley limiter resulting in no operation of compressor. Almost all cases are caused by excessive multi V-belt movement. Another cause might be driving the vehicle without refrigerant
When performing maintenance, it is important to use the correct tools and equipment and to understand what to check. What’s more, it is very important that equipment is regularly maintained for efficient, clean operation. Without regular servicing it is impossible to know the state of the refrigerant inside, which increases the risk of charging dirty and wrong refrigerant or oil. This will result in unhappy motorists demanding compensation for system failure.