Automotive Air Conditioning
How does it work? Where does the cold air come from? Modern refrigeration uses refrigerant to absorb heat and transfer heat and shed heat. Absorb, Transfer, Shed,- Absorb, Transfer Shed. Got it? It is a cycle of heat, or a heat cycle. The refrigerant absorbs heat from the interior of the vehicle in a component called the evaporator. Air is pushed (sometimes pulled) across the evaporator and since the evaporator is colder than the air coming across it, heat (from the air) is absorbed by the evaporator, and the resulting action is "cold" air being blown into the passenger compartment. However, this "cold" air is really just the same old air, but with the heat removed, or absorbed. Remember from science class-"heat moves from hot to cold". Now the refrigerant must move along to the next part of the A/C system, because the compressor is pulling it toward itself. Once inside the compressor, a tremendous amount of compression occurs, and the refrigerant travels at high pressure to the condenser. Remember all the heat we absorbed in the evaporator? The condenser is going to help us get rid of it. Since the compressor has increased our pressure, the result is an enormous amount of heat loss across the face of the condenser. As the refrigerant pushes on it's way out of the condenser, it has shed all the heat that was absorbed inside the vehicle. Still under high pressure, and with all it's heat removed, the refrigerant is now "hungry" for heat, so let's send it back inside to absorb more heat from inside the vehicle. This is accomplished simply by dropping the pressure with a small valve or fixed orifice. Once the pressure is reduced, the refrigerant enters the evaporator where it readily absorbs more heat. The heat cycle is complete. Of course there are more complexities involved with this heat cycle, such as the change of state that occurs in the refrigerant. It's bit larger than the scope of this article, as this is intended for the consumer, not the scientist.
These 5 Major Components are found on all modern A/C and
1) The Compressor is the hardest
working piece of the A/C system. Rotated by the engine, it converts
mechanical energy into refrigerant flow. The traditional design
consists of pistons and valves. Others have vanes and some have
scrolls. Considerable heat is generated by a compressor, and the
cold refrigerant returning to it is vital to it's longevity. If an
A/C system is not full to capacity, the compressor is not receiving
enough cold refrigerant and oil, and overheating of moving parts and
seals is occurring, and a shortened compressor life is inevitable.
2) The Condenser receives the high
pressure refrigerant from the compressor, and through a series of
small tubes, allows the heat energy contained in the refrigerant to
dissipate to the condenser, and onto the air as it rushes past. The
condenser is strategically located to receive the coolest air
possible (in front of the radiator, never behind). Air flow is also
a very important concern, no air flow = no heat transfer.
3) The Expansion Valve has one
simple job. Drop the pressure. Pressures as high as 200-300 psi are
quite common, but by the time the refrigerant sneaks through he
valve, the pressure has dropped to 20-30 psi. This drastic pressure
change allows the refrigerant to be very cold, and hungry for heat.
4) The Evaporator receives the cold,
low pressure refrigerant from the expansion valve and allows it to
flow from the "bottom-up". This enhances the heat absorption and
allows evaporation to occur effortlessly. As the hot air from the
passenger compartment is directed over the evaporator, there is
enough heat (in the air) to boil the refrigerant. An enormous amount
of heat energy is absorbed this way.
5) The Drier performs 3 important jobs. As
the heat load for an A/C increases or decreases, the refrigerant
needs to expand or contract. The receiver drier allows a little
"head space" for this to occur. Similarly, when conditions are cool,
the drier "gives back" so the system doesn't run out of refrigerant.
Located inside the drier are fabric pouches that contain silicon
beads that are able to absorb moisture and small levels of acid. The
plumbing in the drier acts like a liquid/vapor separator to insure
only liquid exits the drier.
The rest of the system is made
up of hoses and pipes, wiring, switches, modules, motors, fans,
doors, actuators and of course the refrigerant. All vehicles have
most of these additional items, and they will vary widely from
vehicle to vehicle.
Installation of air conditioning is
possible in most newer cars and trucks. Factory A/C look is
simulated, and in some cases factory components are used. Older
muscle cars are also popular installation projects.
Evaporator smells can be very
intense. The evaporator offers an environment that is dark, moist,
quiet, and has a supply of "food" being pumped into it. If mold or
mildew gets a foothold, it can be difficult to get rid of. New
products now emerging on the market have finally given some relief
to this problem. Depending on the smell, sources for the problem can
sometimes be located. Synthetic products can "brew-up" really nasty
smells if they are leaking in the evaporator. Other times dead
rodents are extracted from inside. Lots of smells. Lots of
The Inspection is a mandated (by State
of California) list of items to check on an A/C system before any
A/C work can be completed. We take it seriously. Others do not. This
is the inspection form we use.
Should I Retrofit My A/C?
Absolutely. But only when the time is right. When a compressor is
replaced with a receiver drier or accumulator, the time for retrofit
analysis has arrived. Some older cars may not exhibit good
performance after retrofit. Others may need additional fans or other
component upgrades. The newer the car, the better the retrofit will
be. However, retrofitting an A/C on a car that has 80,000 miles on
it, the original compressor, and a worn fan clutch means: 1) poor
A/C performance 2) compressor failure within a year. I've seen it
over and over. I DO NOT RECOMMEND RETROFITTING AN OLD COMPRESSOR TO
A NEW REFRIGERANT! EVER!
Dye was once a dark red syrup that was injected
into an A/C. Not very easy to see and quite messy to use. These days
dyes have come a long way. Modern dye is lime green in color, and is
easily injected into an A/C system. No mess (usually). After several
hours or days, the dye can be spotted and a leak repair made. But
that's not the best part- the dye "fluoresces" in the presence of
ultra violet light. So it literally shines and shows itself even
around dark and greasy dirty areas. Dye can be very useful in
finding stubborn leaks that occur over time, or during certain
conditions such as only during high heat loads, only during cold
weather, only when a fitting experiences contraction etc. Simply
invaluable. But to find a leak instantaneously, the "sniffer" must
Heated Diode leak detector
is an very accurate "sniffer" type detector that alerts the
technician to a leak that is occurring at that very second. No
waiting, no dyes, no rechecking after several hours. Instant
results. Fantastic for finding and fixing leaks, and for QC'ing a
repair before releasing a vehicle back to the customer. However,
when the leak occurs only at night, or only at freeway speeds, or
only during winter inactivity, the dye is the leak finding tool of
Stop Leak for an A/C? Polymers
have been developed that have allowable characteristics to remain in
liquid form in the refrigeration cycle. Upon contact with moisture,
the polymer will harden, and form a "scab" , slowing or stopping the
leak. The problem is, if your system is old, has been serviced a few
times, has leaked down a few times, it probably has moisture in it.
Since the polymer reacts with moisture, if you install the stop
leak, you've now filled your A/C with plastic! No more leaks. No
more A/C! Do not use stop leak. It will not save you Additionally,
professional refrigerant recovery equipment is vulnerable to damage
from this polymer as well, and your A/C shop may ask you to take
your car elsewhere if stop leak is found to be in your system.
Enhancing Products are available. Some allow greater heat transfer by reducing surface tension of the oil. Some target specific smells that accumulate in the evaporator. If it's on the market, have know about it, have read the research, and have it in stock.
How does it work?