Preventing Air Conditioner Failure

There are two things most people know about automotive air conditioning. You cannot do without it [in South Louisiana] and it is expensive to repair. The first is a fact the second can often be prevented.

Many of the large repairs we see on automobile air conditioning, include compressor failures. When a vehicles compressor fails there is a cause. Very often the cause is rooted in improper previous service and ignoring the warning signs. By recognizing the warnings, vehicle compressor failure can be greatly reduced.

There can be dozens of reasons for an automobile air conditioner to stop cooling. One of those reasons is a leak. The refrigerant leaks out and the car stops cooling. The old method of "adding some Freon" will not work, it can quickly do considerable damage.

A leak and low charge is one reason for the unit to stop cooling. It is by no means the only. An electronic condenser fan turning too slowly can very quickly increase compressor pressure to a dangerous level. Most automotive systems will shut down and stop cooling. Adding more refrigerant to such a system will destroy the compressor. The original problem was a fan repair.

Modern vehicle systems are very small, compared to just a few years ago. Up to 80 ounces of refrigerant was used in older systems. Today many systems operate on less than 12 ounces. Adding 12 ounces to an 80 ounce system resulted in a 15% overcharge. Adding the same 12 ounces to a 12 ounce system results in a 100% over charge and damage.

Making the situation far more complex is the wide usage of variable displacement and computer-controlled compressors. These units vary their pressures constantly and reading a set of gauges will not produce the right charge. A unit can be seriously over or under charged and not indicate it on refrigeration gauges.

To properly charge such a system, it must be fully evacuated and the precise amount specified added. This requires a recycle machine to extract the old charge, a charging cylinder and a precise digital scale.

If the system is actually low, repair can still be fairly straight forward and inexpensive. The leak must be found, corrected and the system properly recharged. Many times this may involve replacing a switch, hose, O-ring or an evaporator core. Properly diagnosed and repaired, the leak will cause no further problem. Ignoring the leak and adding refrigerant will often add the price of a compressor to the job.

Preventing compressor failure involves a quick response to the warning signs:

    The air conditioner does not cool as well as before


    The vehicle warms up when sitting and idling


    The system warms up after driving a distance


    There is a noise when the system is turned on or off


    The air conditioner stops cooling


    Water is dripping inside the vehicle

How long should a car's A/C compressor last?

For many of us, as long as our car is running well, we may not think about the hundreds of parts working together under the hood to bring us our creature comforts. The air conditioning compressor is one of those parts that typically gets a lot of usage and provides that critical cool air on hot summer days. The air-conditioning compressor does exactly what its name says -- it compresses refrigerant and sends it to your car's air condenser. The entire process is powered by your engine's drive belt (or belts). The highly pressurized liquid refrigerant converts to a gas and is circulated into tubes where the heat from the gas is quickly released, causing it to cool. The cooled gas then reverts back into liquid form as it returns to the compressor. The cooled gas is used to chill the car's cabin air.
As with any other part on a car, it's difficult to determine exactly how long any one specific component will ultimately last, but there are some factors that help determine how long a compressor will be able to do its job. The first is the age of the car. Most modern cars have air-conditioning systems that are considered reliable, so major issues are rare. But similar to other car parts, as a car's age and mileage begin to add up, you can expect that the wear and tear over the years will cause parts to fail or malfunction. In the case of the A/C compressor, this can mean little or no cool air coming from the system.
To keep your car's compressor in shape throughout the year, it's recommended that you run the A/C compressor regularly, to keep the system working properly and to extend its longevity. Many cars use the A/C compressor for functions of heating and ventilation in the defrost cycle, too. But if your car doesn't, you should run the compressor for at least 10 minutes each month, even during the winter months.
One last point to note: If the compressor has already been replaced in your vehicle, the lifecycle may not be quite as long as the factory original part. Many aftermarket auto parts websites will quote a one- or two-year warranty on the part -- but, of course, they can certainly last much longer with the proper care.
So, if you notice that your car's air conditioning system isn't putting out any cold air, or minimal cold air, a dysfunctional or broken compressor could be the culprit (among several other possibilities). Just remember that compressors function at high pressures, involve liquid refrigerant and require special tools to service -- it may be best to leave changing the compressor to an expert mechanic.
Source: howstuffworks.com

Ejector Cycle - Denso


In 2003, DENSO introduced the world’s first refrigeration unit with an ejector cycle for mid- and large-sized trucks.
The newly developed ejector cycle is a high-efficiency refrigeration cycle with a significantly improved energy consumption efficiency, achieved by using a small injector called an ejector. The refrigeration units with the ejector cycle increase energy consumption efficiency by 50 percent compared to previous models.
The ejector cycle can be used, in principle, in the refrigeration cycle of car air conditioners, room air conditioners, and refrigerators. DENSO will continue to work on commercializing these new products.
How it works:
  • The ejector, used in the ejector cycle instead of a conventional expansion valve, expands high-pressure refrigerant by using energy which previously was lost.
  • A gas-liquid separator separates expanded refrigerant into gas and liquid so that gas refrigerant is directly drawn into the compressor at a higher pressure while liquid refrigerant flows into the evaporator to exchange heat with air.
Benefits and Features
  • Small compressor power consumption
    • The ejector uses energy, which is lost in a conventional expansion valve, to increase the pressure of refrigerant drawn into the compressor, resulting in compressor power consumption almost two-thirds smaller than the power consumption required in a conventional expansion valve cycle.
  • High evaporator performance
    • Only liquid refrigerant flows into the evaporator, reducing pressure loss and improving evaporator performance.
  • Small size and light weight
    • Compared to the expansion valve cycle with similar refrigeration capacity, the overall weight of the ejector cycle is reduced by 40 percent thanks to the remarkable minimization of the compressor, condenser and evaporator. The weight reduction also increases fuel efficiency by 60 percent.

HVAC Unit - Denso

The heating, ventilating and air conditioning (HVAC) unit, installed in a vehicle’s instrument panel, is required to be smaller, quieter and more efficient. DENSO strives to satisfy all of these requirements as a leader in this field. 

The HVAC unit includes an air filter, blower fan, evaporator and heater core, and generates conditioned air to make the passenger cabin comfortable.

HVAC Unit Structure

DENSO Technology – Leading the World
  • In 1994, DENSO introduced the world’s first film-door HVAC unit, which uses high-accuracy film doors to switch air flows, reducing the size and weight of the unit and achieving more comfortable air temperature control (see below).
  • The two-layer flow HVAC unit, DENSO first introduced in 1997, can circulate internal warm air in the lower half of the passenger cabin, and route external fresh air through the upper half, improving heating efficiency and more effectively preventing window fogging (see below).
Film-door HVAC Unit


Two-layer Flow HVAC Unit

Heater Core - Denso

The heater core reheats a portion of the air cooled by the evaporator by exchanging heat with engine-cooling water. The reheated air is mixed with the remaining evaporator-cooled air and the mixed air is blown into the vehicle cabin.
DENSO Technology – Leading the World


  • In 2002, DENSO introduced a smaller, lighter heater core – 27 mm in width – achieving the same performance as the company’s conventional 46 mm heater core. The new heater core has the world’s thinnest tube plate of 0.2 mm.
Benefits and Features
  • Small size (thin width)
    • Thinner tube (1.3 mm) and smaller fin height (3.9 mm) improves heat exchange efficiency.
  • Light weight
    • The tube’s zinc (Zn) diffusion layer improves corrosion resistance, resulting in very thin tube plate thickness (0.2mm).

Evaporator - Denso

The evaporator cools and dehumidifies air inside the vehicle by exchanging heat with a refrigerant. The evaporator is integrated into the HVAC unit located in the instrument panel.
DENSO’s small & light evaporator improves both interior comfort and fuel economy.
DENSO Technology – Leading the World

  • In 2002, DENSO introduced the thinnest evaporator of its kind in the world. This small and light evaporator — 38 mm in width— has the world’s thinnest tubes and thinnest tube plates.
Benefits and Features
  • Small size (thin width)
    • Thinner tube (1.7 mm) and shorter fin height (5 mm) improves heat exchange efficiency.
  • Light weight
    • The tube’s zinc diffusion layer improves corrosion resistance, resulting in very thin tube plate thickness (0.2 mm).
  • High performance
    • Separating the tubes and the tanks increases the tank flow path area and reduces refrigerant pressure loss.
  • Excellent draining capability
    • Slits on the outer fins make draining easier
Refrigerant Flow in Evaporator

Tube Cross Section



Condenser - Denso

By exchanging heat with air, the condenser cools the high-temperature, high-pressure gas refrigerant sent from the compressor and condenses it into liquid refrigerant. This heat exchange allows the air conditioning system to emit the heat absorbed by the evaporator from inside the vehicle to the outside.

DENSO’s high-performance condenser reduces the required compressor power, resulting in improved fuel economy.
DENSO Technology – Leading the World
  • In 1996, DENSO introduced a condenser that integrated the condenser and subcooler. This condenser was the first in the world to have the modulator (receiver) integrated with the condenser tank (see below).
  • In 2002, DENSO introduced a new condenser with a subcool part, featuring the world’s thinnest tube (1 mm) and lowest fin height (5.4 mm).
Benefits and Features
  • High performance
    • The subcooler integrated with the condenser further cools the liquid refrigerant, resulting in increased refrigerant enthalpy and improved evaporator cooling performance.
    • Thinner tubes and fins improve the heat exchange rate.
      Smaller header tank and lower side plate height increase the effective heat exchange area of the core part that exchanges heat, without increasing the installation space.
  • Small size, light weight and easy installation
    • Integrated modulator with condenser tank.
    • The tube’s zinc diffusion layer improves corrosion resistance, resulting in reduced tube plate thickness.
Condenser with a Subcooler Part

Swash Plate Fixed Displacement Compressor - Denso

  The fixed displacement compressors compress refrigerant in accordance with the engine rotation.
DENSO provides three types of fixed displacement compressors– swash plate type, scroll type and vane type.
In the swash plate fixed displacement compressor, a swash plate, fixed to the shaft, rotates to reciprocate pistons, and the reciprocating pistons compress refrigerant. 

DENSO Technology – Leading the World
  • In 1997, DENSO introduced a swash plate fixed displacement compressor that applied a newly developed two-layer surface treatment coat to a swash plate, significantly improving the swash plate abrasion resistance while maintaining its sliding capability, resulting in longer life.
  • In 2003, DENSO used new materials for the two-layer surface treatment coat of the swash plate, further improving its abrasion resistance even with a small amount of lubricant.

Benefits and Features

  • High durability
    • The two-layer surface treatment coat for the swash plate gives the compressor high durability.
  • Small size and light weight
    • Gaskets and M6 bolts are used to hermetically seal the compressor, reducing the compressor diameter.
  • Low noise, vibration and high compressor efficiency
    • DENSO developed a unique structure to tightly fix the swash plate to the housing, reducing the noise and vibration caused by the swash plate rotation, while allowing the swash plate to smoothly and stably rotate. The smooth, stable rotation of the swash plate results in high compressor efficiency.
DENSO’s Latest Model Structure


Scroll fixed Displacement Compressor

The fixed displacement compressors compress refrigerant in accordance with the engine rotation.
DENSO provides three types of fixed displacement compressors– swash-plate type, scroll type and vane type.
In the scroll fixed displacement compressor, a movable scroll rotates to change the volume of space between the movable scroll and the fixed scroll, compressing the refrigerant. 
DENSO Technology – Leading the World
In 1997, DENSO launched the world’s first scroll fixed displacement compressor that adopted a centrifugal oil separator to reduce the amount of oil contained in circulating refrigerant, improving the efficiency of the air conditioning system. 


Benefits and Features
  • Small size and light weight
    • DENSO improved the housing, giving it a thinner wall while maintaining its strength, making it smaller and lighter.
    • The fixed scroll functions as a compression chamber wall, resulting in an even smaller and lighter compressor.
  • High compressor efficiency and high durability
    • The oil separator removes most of the oil from the refrigerant when it is discharged from the compressor. That oil is then supplied to the compressor’s sliding parts, maintaining lubrication of the compressor and increasing efficiency as well as durability.
    • The optimized shape of the scrolls further improves the compressor efficiency.
    • The reduced number of parts in the sliding section, including a simple rotation-preventive mechanism, reduces energy loss caused by sliding.
  • Low noise and vibration
    • The reduced number of parts in the sliding section reduces mechanical noise.
    • The optimized housing shape reduces the pulsation of refrigerant discharged from the compressor.
DENSO’s Latest Model Structure

Externally Controlled Variable Displacement Compressor - Denso

The variable displacement compressor has a swash plate that rotates to reciprocate pistons, which compresses refrigerant. The variable displacement compressor change the swash plate angle to change the refrigerant displacement.
The externally controlled type variable displacement compressor changes the swash plate angle in accordance with an electrical signal from an electric control unit.
DENSO’s externally controlled variable displacement compressor manages displacement by controlling refrigerant differential pressure before and after a throttle at the discharge side; achieving precise cooling capability control in accordance with cabin environment and driving conditions. 


DENSO Technology – Leading the World
  • DENSO developed the world’s first technology that controls refrigerant displacement from almost zero percent to 100 percent. Using this technology, in 1997, DENSO launched the world’s first externally controlled variable displacement compressor with a damper limiter (DL) pulley, instead of a magnetic clutch, making the compressor smaller, lighter and more reliable.
  • In 2001, DENSO launched the world’s first externally controlled variable displacement compressor with an electromagnetic control valve that controls refrigerant differential pressure before and after a throttle at the discharge side, in accordance with an electric signal from the engine ECU or air conditioner ECU. By controlling refrigerant discharge pressure rather than refrigerant suction pressure, the engine torque used for the compressor can be estimated. This allows the compressor to be controlled in connection with engine management to reduce fuel consumption.
  • In 2001, DENSO launched an even lighter variable displacement compressor with a resin-made DL pulley.
  • In 2003, DENSO launched the world’s first externally controlled variable displacement compressor with a rotary valve as a suction valve, instead of a conventional lead valve plate. This improved compressor efficiency by approximately 10 percent.
Benefits and Features
  • Small size and light weight
    • The externally controlled variable displacement compressor (5SER09) with resin-made DL pulley achieves the world’s lightest weight for equivalent displacement compressors.
      DENSO improved the housing to have a thinner wall while maintaining its strength, contributing to a smaller and lighter compressor.
  • High compressor efficiency
    • The world’s first rotary valve reduces pressure drop of refrigerant gas drawn into compression chambers, and prevents heating of the refrigerant gas. This enables the compressor to draw a larger amount of refrigerant into the compressing chambers, increasing compressor efficiency by approximately 10 percent when compared to a conventional compressor.
  • Precisely controllable in connection with engine management
    • Using DENSO-developed electromagnetic control valve, refrigerant displacement is controlled in accordance with the amplitude of engine torque used for the compressor. This maximizes engine efficiency.
  • Low noise and vibration
    • The rotary valve and the housing’s muffler structure significantly reduce the pulsation of refrigerant gas pulled into the compression chambers.
  • High reliability
    • The pistons are hollow, enabling the compressor to control refrigerant displacement at a maximum of 11,000 revolutions per minute, at high engine speed. This prevents the pistons from disturbing the swash plate inclination control even at the high engine speed.
DENSO’s Latest Model (5SER09) Structure