Air Conditioner - How Does it Work? Explained By the Pros
Would you like to know how a vehicle’s air conditioner works and the
first things to check when it doesn't? The system looks complicated, but
it's not, once you know how it delivers cold air you will be better informed
when problems occurs and how to fix it, or understand more on what a garage is telling you when having it repaired.
This step by step guide will help you know if you
can fix the problem yourself, or when a repair garage is best, let's begin.
A climate control system is designed to operate the various settings to
improve occupant comfort, these controls may differ in appearance, but perform
the same task: fan speed, vent mode (defrost, mid and floor) and temperature control.
System: The diagram below shows the entire system and refrigerant flow;
these systems are closed (sealed) which continuously re-circulates the
refrigerant. The receiver dryer or accumulator is where the refrigerant is
cleaned and dried.
Once compressed, the R134a travels to the condenser where it is cooled
and transformed into a liquid state from the compressor which takes the spent
gas from the evaporator and feeds it into the compressor via the low side hose
Once entering the compressor the R134a is compressed and then
transferred into the high side hose which connects from the compressor to the condenser. This
condenser sits right in front of the engine's radiator so it can get air drawn
through it much like the
radiator by the
The R134a is then pushed through the condenser which looks kind of like a
radiator only a bit smaller and then cooled back into the
liquid form and still under high pressure form the compressor.
Now the cooled R134a still under high pressure is forced through an expansion
valve or an orifice tube where the magic cold happens by the pressure drop.
This pressure drop occurs inside the evaporator core which looks like a small
squat radiator which is located inside the vehicle. Once the refrigerant has
spent its cold charge it is gathered into the low side hose and onto the
compressor once again being processed.
Maintenance and Operation: As your vehicle ages the refrigerant level should be maintained and added too,
insuring that air flowing into the occupant cabin is cold,
especially on those hot summer days. Because this system is pressurized, kind of
like a tire, it will need to be
recharged as it ages. Refrigerant charging kits are available at many auto
parts stores and
Amazon. Recharging the system is not to difficult and can be done in about 20
The low side pressure port is used to charge the system and is always larger
in size than the high side pressure port. You can see the high side pressure
line is always smaller than the low side pressure line in the image below. Some refrigerant lines
will have an insulation wrap on the low side line; this is
usually due to the location of the engine exhaust being in close vicinity.
The compressor is the main mechanical part of the system with internal
workings inside the unit that is driven by the engine's serpentine belt. When
there is a weird noise when the a/c is on the compressor or blower fan is
probably the problem and most likely due to a mechanical failure. When the
compressor stop working the system will blow warm air and when this happens the
compressor needs to be replaced.
When you turn the system on a voltage supply is given to the climate
controller, the blower motor fan and the compressor clutch or internal valve. These components then begin to operate connected through a climate control wiring harness fuse and relay.
Some condensers are designed with a receiver dryer attached which acts
as a refrigerant cleaner/moisture remover which helps the system last longer.
Some systems will have an accumulator that does the same job, each car
maker is a little bit different, but achieve the same goal.
Leaves and dirt can
get logged in the condenser hindering its performance. I use a garden hose to
clean the condenser with a high pressure nozzle from time to time and it works
really well which helps the air conditioner work more efficiently.
Some air conditioner systems have a separate fan for the condenser instead of
the radiator cooling fan, or they will have an additional fan to help the
radiator fan cool the refrigerant. These fans are controlled by the climate control computer which gives a command to the control relay to power the fan on. When these fans fail the
system will not cool as well and should be replaced.
A serpentine belt is used to rotate the compressor pump by the engine's
serpentine belt and belt tensioner, once the engine is running the air
conditioner can be turned on. The internal workings of the compressor include
reed valves and an eccentric vane pump.
A hybrid and electric vehicle’s
compressor is powered by the vehicle's battery pack not the engine, a small
electric motor is fitted inside of the compressor which makes it operate. These compressors have a pair
of large gauge wires form the compressor controller and not a serpentine belt.
Check out the picture below.
You can visually see most system leaks because it uses a peg
oil along with the refrigerant, which are mixed together as they travel throughout the
system. This oil is used to lubricate the internal vanes and reed valves of the
pump. See what a refrigerant leak looks like below.