Today, as we drive our cars, a great many of us, can enjoy the same comfort levels that we are accustomed to at home and at work. With the push of a button or the slide of a lever, we make the seamless transition from heating to cooling and back again without ever wondering how this change occurs. That is, unless something goes awry.
Since the advent of the
car air con system in the 1940's, many things have
undergone extensive change. Improvements, such as computerized
automatic temperature control (which allow you to set the desired
temperature and have the system adjust automatically) and
improvements to overall durability, have added complexity to today's
modern air conditioning system. Unfortunately, the days of
"do-it-yourself" repair to these systems, is almost a thing of the
past.
To add to the complications, we
now have tough environmental regulations that govern the very
simplest of tasks, such as recharging the system with refrigerant
R12 commonly referred to as FreonŽ (Freon is the trade name for the
refrigerant R-12, that was manufactured by DuPont). Extensive
scientific studies have proven the damaging effects of this
refrigerant to our ozone layer, and its manufacture has been banned
by many countries that have joined together to
sign the Montreal Protocol, a landmark agreement that was introduced
in the 1980's to limit the production and use of chemicals known to
deplete the ozone layer.
Now more than ever, your auto
mechanic is at the mercy of this new environmental legislation. Not
only is he required to be certified to purchase refrigerant and
repair your air conditioner, his shop must also incur the cost of
purchasing expensive dedicated equipment that insures the capture of
these ozone depleting chemicals, should the system be opened up for
repair. Simply put, if your mechanic has to spend more to repair
your vehicle - he will have to charge you more. Basic knowledge of
your air conditioning system is important, as this will allow you to
make a more informed decision on your repair options.
Should a major problem arise
from your air conditioner, you may encounter new terminology. Words
like "retrofit" and "alternative refrigerant" are now in your
mechanics glossary. You may be given an option of "retrofitting", as
opposed to merely repairing and recharging with Freon. Retrofitting
involves making the necessary changes to your system, which will
allow it to use the new industry accepted, "environmentally
friendly" refrigerant, R-134a. This new refrigerant has a higher
operating pressure, therefore, your system, dependant on age, may
require larger or more robust parts to counter its inherent high
pressure characteristics. This, in some cases, will add
significantly to the final cost of the repair. And if not performed
properly, may reduce cooling efficiency which equates to higher
operating costs and reduced comfort.
Vehicles are
found to have primarily three different types of air conditioning
systems. While each of the three types differ, the concept and
design are very similar to one another. The most common components
which make up these automotive systems are the following:
COMPRESSOR,
CONDENSER,
EVAPORATOR,
ORIFICE TUBE,
THERMAL EXPANSION VALVE ,
RECEIVER-DRIER,
ACCUMULATOR.
Note: if your
car has an Orifice tube, it will not have a Thermal Expansion Valve
as these two devices serve the same purpose. Also, you will
either have a Receiver-Dryer or an Accumulator, but not
both.
COMPRESSOR
Commonly referred to as the heart of the system, the
compressor is a belt driven pump that is fastened to the engine. It
is responsible for compressing and transferring refrigerant
gas.
The car air con system is split into two sides, a high
pressure side and a low pressure side; defined as discharge and
suction. Since the compressor is basically a pump, it must have an
intake side and a discharge side. The intake, or suction side, draws
in refrigerant gas from the outlet of the evaporator. In some cases
it does this via the
Accumulator.
Once the refrigerant is drawn into the suction side,
it is compressed and sent to the
condenser,
where it can then transfer the heat that is absorbed from the inside
of the vehicle.
CONDENSER
This is the area in which heat dissipation occurs.
The condenser, in many cases, will have much the same appearance as
the radiator in you car as the two have very similar functions. The
condenser is designed to radiate heat. Its location is usually in
front of the radiator, but in some cases, due to aerodynamic
improvements to the body of a vehicle, its location may differ.
Condensers must have good air flow anytime the system is in
operation. On rear wheel drive vehicles, this is usually
accomplished by taking advantage of your existing engine's cooling
fan. On front wheel drive vehicles, condenser air flow is
supplemented with one or more electric cooling fan(s).
As hot compressed gasses are introduced into the top
of the condenser, they are cooled off. As the gas cools, it
condenses and exits the bottom of the condenser as a high pressure
liquid.
EVAPORATOR
Located inside the vehicle, the evaporator serves as
the heat absorption component. The evaporator provides several
functions. Its primary duty is to remove heat from the inside of
your vehicle. A secondary benefit is dehumidification. As warmer air
travels through the aluminum fins of the cooler evaporator coil, the
moisture contained in the air condenses on its surface. Dust and
pollen passing through stick to its wet surfaces and drain off to
the outside. On humid days you may have seen this as water dripping
from the bottom of your vehicle. Rest assured this is perfectly
normal.
The ideal temperature of the evaporator is 32°
Fahrenheit or 0° Celsius. Refrigerant enters the bottom of the
evaporator as a low pressure liquid. The warm air passing through
the evaporator fins causes the refrigerant to boil (refrigerants
have very low boiling points). As the refrigerant begins to boil, it
can absorb large amounts of heat. This heat is then carried off with
the refrigerant to the outside of the vehicle. Several other
components work in conjunction with the evaporator. As mentioned
above, the ideal temperature for an evaporator coil is 32° F.
Temperature and pressure regulating devices must be used to control
its temperature. While there are many variations of devices used,
their main functions are the same; keeping pressure in the
evaporator low and keeping the evaporator from freezing; A frozen
evaporator coil will not absorb as much heat.
PRESSURE REGULATING
DEVICES
Controlling the evaporator temperature can be
accomplished by controlling refrigerant pressure and flow into the
evaporator. Many variations of pressure regulators have been
introduced since the 1940's. Listed below, are the most commonly
found.
ORIFICE TUBE
The orifice tube, probably the most commonly used,
can be found in most GM and Ford models. It is located in the inlet
tube of the evaporator, or in the liquid line, somewhere between the
outlet of the condenser and the inlet of the evaporator. This point
can be found in a properly functioning system by locating the area
between the outlet of the condenser and the inlet of the evaporator
that suddenly makes the change from hot to cold. You should then see
small dimples placed in the line that keep the orifice tube from
moving. Most of the orifice tubes in use today measure approximately
three inches in length and consist of a small brass tube, surrounded
by plastic, and covered with a filter screen at each end. It is not
uncommon for these tubes to become clogged with small debris. While
inexpensive, usually between three to five dollars, the labor to
replace one involves recovering the refrigerant, opening the system
up, replacing the orifice tube, evacuating and then recharging. With
this in mind, it might make sense to install a larger pre filter in
front of the orifice tube to minimize the risk of of this problem
reoccurring. Some Ford models have a permanently affixed orifice
tube in the liquid line. These can be cut out and replaced with a
combination filter/orifice assembly.
THERMAL EXPANSION VALVE
Another common refrigerant regulator is the thermal
expansion valve, or TXV. Commonly used on import and aftermarket
systems. This type of valve can sense both temperature and pressure,
and is very efficient at regulating refrigerant flow to the
evaporator. Several variations of this valve are commonly found.
Another example of a thermal expansion valve is Chrysler's "H block"
type. This type of valve is usually located at the firewall, between
the evaporator inlet and outlet tubes and the liquid and suction
lines. These types of valves, although efficient, have some
disadvantages over orifice tube systems. Like orifice tubes these
valves can become clogged with debris, but also have small moving
parts that may stick and malfunction due to corrosion.
RECEIVER-DRIER
The receiver-drier is used on the high side of systems that use a
thermal expansion valve. This type of metering valve requires liquid
refrigerant. To ensure that the valve gets liquid refrigerant, a
receiver is used. The primary function of the receiver-drier is to
separate gas and liquid. The secondary purpose is to remove moisture
and filter out dirt. The receiver-drier usually has a sight glass in
the top. This sight glass is often used to charge the system. Under
normal operating conditions, vapor bubbles should not be visible in
the sight glass. The use of the sight glass to charge the system is
not recommended in R-134a systems as cloudiness and oil that has
separated from the refrigerant can be mistaken for bubbles. This
type of mistake can lead to a dangerous overcharged condition. There
are variations of receiver-driers and several different desiccant
materials are in use. Some of the moisture removing desiccants found
within are not compatible with R-134a. The desiccant type is usually
identified on a sticker that is affixed to the receiver-drier. Newer
receiver-driers use desiccant type XH-7 and are compatible with both
R-12 and R-134a refrigerants.
ACCUMULATOR
Accumulators are used on systems that accommodate an orifice tube
to meter refrigerants into the evaporator. It is connected directly
to the evaporator outlet and stores excess liquid refrigerant.
Introduction of liquid refrigerant into a compressor can do serious
damage. Compressors are designed to compress gas not liquid. The
chief role of the accumulator is to isolate the compressor from any
damaging liquid refrigerant. Accumulators, like receiver-driers,
also remove debris and moisture from a system. It is a good idea to
replace the accumulator each time the system is opened up for major
repair and anytime moisture and/or debris is of concern. Moisture is
enemy number one for your A/C system. Moisture in a system mixes
with refrigerant and forms a corrosive acid. When in doubt, it may
be to your advantage to change the Accumulator or receiver in your
system. While this may be a temporary discomfort for your wallet, it
is of long term benefit to your air conditioning system.
REFRIGERANT
Regardless of the type, all air conditioning systems function according to a basic law of physics that states ‘a fluid absorbs heat as it changes from a liquid to a gas, and a vapor releases heat as it changes from a gas to a liquid.’ In an A/C system, refrigerant is the transfer medium used to absorb the heat inside the passenger compartment and release it to the outside air. Refrigerant is a tasteless, odorless gas with an ability to change state rapidly within a specific temperature range. It is also oil soluble and non-corrosive. While there are scores of refrigerants on the market, there are only two types approved by vehicle manufacturers: R-12 and R-134a.
R-12, commonly referred to as Freon, has long been used as the refrigerant in all automotive A/C systems. However, R-12 contains chlorine, which is the primary cause of ozone layer damage. Consequently, legislation was passed calling for a halt in R-12 production by 1996. Long before the phase-out of R-12 began however, the automotive industry conducted extensive research and development to find an environmentally friendly alternative. They ultimately selected R-134a as the new refrigerant, and began using it in vehicles as early as 1992.
R-134a is similar to R-12, in that it absorbs, transfers, and releases heat efficiently. It is also non-flammable, and mixes well with oil, just like R-12. However, R-134a does have some unique characteristics.
- R-134a requires a special synthetic lubricant since it does not mix with mineral oil (standard R-12 lubricant).
- R-134a operates at higher discharge pressures than R-12. Therefore, systems using R-134a may not cool as well as R-12 when the vehicle is idling for extended periods (e.g. heavy traffic).
- R-134a and R-12 cannot be mixed, which is why separate equipment is needed to service vehicles using either refrigerant.
Depending on the vehicle, refrigerant capacity can range anywhere from about 28 ounces (1.75 lbs.) to as much as 64 ounces (4.00 lbs.) or more. To avoid an improper charge, always consult the manufacturer's specifications for refrigerant capacity. An improper charge will cause reduced system performance, and may even result in system damage.
REFRIGERANT OIL
In order to function properly, an A/C system requires the appropriate type and amount of oil. In addition to lubricating the compressor, refrigerant oil also maintains the operation of the expansion valve on systems so equipped. Since the oil is transported through the system by the refrigerant, it has to be compatible with the type of refrigerant being used. Mineral oil is the lubricant used for all R-12 systems, while R-134a systems use synthetic oils such as PAG (polyalkylene glycol) and POE (polyolester).
An Air Conditioning service takes approximately 1 hours and consists of the following:
-
Check pressures
-
Check all controls
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Pressure test system using OFN (Oxygen Free Nitrogen)
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Check of condenser
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Check of all hosing and pips
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Check of compressor
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Check of compressor drive belt
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Recover old A/C
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Vacumm AC system
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Recharge system with correct refrigerant
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Check vent temperature and refrigerant pressures
Prices
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Check for leaks and advise £39 inc
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Re-Gas 134a 700g £69 inc
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Re-Gas R12 (rs24) 500g £79 inc
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all re-gasing comes with FREE UV oil.
NEW: We also Re-Gas Office and home units.
