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Replacing
your auto A/C Compressor:
Here's a great
'step-by-step' or 'how to' guide to replace your auto A/C compressor.
If you're not doing the work yourself, this information will provide you
a much better understand what the auto service shop is trying to explain
Potentially
one of the most costly auto A/C repairs is when you have to replace the A/C
compressor. If you're facing that situation now, it's really important
that you understand all the steps that must be followed in order to do the
job properly and get warranty on your replacement compressor. Keep in mind
that the 'steps' we talk about apply to either new or
remanufactured compressors, so there is no difference. You will also
find this information of interest if you're having the work completed by
a service shop (or if you're shopping for a service shop). We'll try to eliminate
all the technical terms to make it easier to understand.
What's
really important to understand before you start is that the A/C system is
just that... it's a system! That means it's only as good as the weakest
link. It also means that all the components in the system must work
together.
To
start, let's have a look at some of the components you should really pay
attention to when you're replacing the A/C compressor. They are:
1) the condenser
2) the accumulator or receive
drier
3) refrigerant or compressor
oil
4) orifice tube or expansion valve
(also called a TXV)
5) hose or line assemblies
6) Before you finish, you must
flush the A/C
system.
You should also give serious consideration to having an
in-line filter installed. (More
about that later) and you may still have to retrofit
the A/C system too!
Let's
start by understanding what happens when the A/C compressor fails and how
it effects the different parts of the system. We will detail the functions
of these various parts and also explain how a blown or seized A/C compressor
can effect them. That way you'll have a real good understanding of how to
go about the replacement of the compressor or be able to better understand
what the service shop may be trying to explain. Remember, we're going to
keep the technical jargon out so it's going to be easy to follow, ok?
To
start, remember that the A/C system is a sealed system. When a compressor
fails (usually because of the lack of oil flow to the compressor)
the internal parts of the compressor 'break up' and are pushed throughout
several parts of the system. This contaminates the system and those parts.
Before replacing the compressor, several other A/C parts have to be checked
or changed. Here's why.
The
Condenser:
The
A/C condenser performs pretty much the same function as an engine radiator,
but the condenser cools the refrigerant (or freon) in the auto A/C system.
Typically, the A/C condenser should be
flushed to remove
any debris. The flushing of the system will remove contaminated compressor
oil and debris scattered throughout the system.
In
more current vehicle applications using high efficiency condensers, you should
understand that they may not be able to be flushed. Why? The passages are
simply too small and much of the debris gets lodged into the tube openings.
In short, it's just impossible to remove all the debris from these condensers
designs. The photo on the left shows a 'cut away' cross section of a typical
high efficiency A/C condenser. You can see for yourself that the tube openings
are extremely small.
SERVICE
Required: Depending on the actual design of the A/C condenser,
it may have to be replaced. If it can be flushed, it's best to use approved
flushing agents that evaporate
quickly and do not leave any residue in the A/C system. The ability
to flush a condenser has to be considered on a case by case basis.
The Accumulator
or Receiver Drier:
Accumulators
and Received Driers are not interchangeable, but they perform the same functions.
This component is in the A/C system to
1) trap, remove and hold moisture
2) filter particles or debris
3) also acts as a reservoir for compressor oil and refrigerant
Typically,
the accumulators are located on the LOW pressure side of the system.
Receiver driers are almost always on the HIGH pressure side, usually in the
liquid line that runs between the condenser and evaporator.
This
detailed illustration will show you exactly where these components are located
in a typical auto A/C system. or a detailed below is an illustration showing
where the A/C accumulator and/or receiver drier would be located on a typical
auto A/C system.
It's
important to remember that one of the main functions of the accumulator or
drier is to absorb moisture from the A/C system. Therefore they include a
desiccant material. Desiccants are typically made from silica gel, and because
of their affinity for water, they make great drying agents. Additionally,
accumulators and driers have filter screens to trap any debris. After
a compressor failure, these filter screens can easily get plugged
with debris. KEEP IN MIND.. some of the components that flow refrigerant
through the system work with openings of less than .050" (fifty thousandths
of an inch). It takes LESS THAN 1/10 of A TEASPOON OF DEBRIS to plug
these components and cause a failure.
SERVICE
Required: Typically, the desiccants have been proven to become saturated
after three to four years of service. Once saturated, they can no longer
absorb moisture. Additionally, there is no way to check the filter screens
for contamination. It is very common for the debris from the compressor failure
to contaminate driers because the debris is carried throughout the system.
Therefore, as a standard practice, accumulators or receiver driers should
be replaced whenever you are replacing the A/C compressor. Consider that
it's much the same as an oil filter on you engine. You change the oil; you
change the oil filter. Like any filter, there is a 'fixed' capacity for how
much debris and contamination any filter can hold. Additionally, if the
accumulator or drier is not replaced, you are probably going to
'void' your compressor warranty.
A/C Compressor
Oil:
Auto
A/C compressor oil is the lifeblood of the a/c system. However, it's interesting
to note that the oil in the A/C system is only there for the compressor.
There are no other components that require internal lubrication; just the
A/C compressor.
There
are different types of A/C compressor oil ranging from PAG, Ester and mineral
(now rarely used). There are also other synthetics that provide many benefits
over the traditional oils. One of the best ones we've used and worked with
is Polymax2. What's unique
about Polymax2 is that it's compatible with all the other compressor oils,
but it is no where near as hygroscopic (meaning is does not
attract or hold moisture... and this is really important!) This oil
is and used is oils on the market and they t are import Up until
the early 1990’s, all auto A/C Systems used a common refrigerant known
SERVICE
Required: It's important to try and remove as much of the contaminated
oil as possible. It's just like having a new engine installed; you don't
reuse the old oil, do you? The same applies to the A/C Compressor oil. You
will have to flush the
A/C system to remove contamination and oil. Replace the oil using new
compressor oil.
The Orifice Tube
or Expansion Valve:
Like
accumulators and driers, orifice tubes and expansion valves are not
interchangeable, but they perform the same function in the auto
A/C system. They simply 'meter' or control the flow of refrigerant.
In
orifice tube systems, it's virtually mandatory that the orifice tube
be removed and inspected. In most cases where the system has sustained a
compressor failure, the inlet screen of the orifice tube quickly gets
plugged with debris. That restricts the flow of both refrigerant and refrigerant
oil.
Expansion
valves are not as easy to inspect. Some designs include inlet screens as
a safety precaution; others do not. There are some 'bench tests' that can
be performed for expansion valves, however they are very difficult to
diagnose when the system is not operating. Therefore, it's not uncommon
to have a compressor replaced only to find out afterwards that the
expansion valve is faulty.
This
illustration will provide you a better look at a typical orifice tube and
expansion valve. Remember, the openings in these valves are very small. They
are usually about .050" (fifty thousandths of an inch) and are quickly plugged
when a compressor fails. As an example, view
this orifice tube that was
pulled from an actual failed compressor repair. Although the orifice tube
that's pictures is extremely plugged, it only takes about 1/10th of a teaspoon
of debris to block the flow of refrigerant and oil in the average auto A/C
system.
SERVICE
Required: Typically, orifice tubes should be replaced. Even small
amounts of debris can cause restrictions in the proper flow or refrigerant.
Expansion valves may have to be replaced. If they are restricted, there is
no repair. If they have no visible signs of contamination or restriction,
they may be tried and tested with the replacement compressor.
A/C Hose
assemblies:
Whenever
replacing your Auto A/C Compressor, pay close attention to all the hose
assemblies. Understand that there are three different hose assemblies on
each vehicle. They are; 1) from the A/C compressor to the condenser; 2)from
the condenser to the evaporator inlet; 3)from the evaporator outlet back
to the A/C Compressor.
Hose
assemblies can be coated internally with oil and contaminants. Each hose
should be dismantles and removed, then flushed as an individual component
to remove all oil and debris that may be in them. Play special attention
to the low side suction hose (from the Evaporator to the A/C Compressor).
Depending on the vehicle and compressor design, it is possible that when
a compressor seizes and 'scatters', debris can be released 'backwards'
into the suction hose. Leaving that debris in the hose (and not flushing
it) will cause it to contaminate your new compressor.
Be
sure that all hose assemblies are cleaned internally prior to installing
your replacement A/C compressor.
SERVICE
Required: Remove all A/C hoses from the vehicle and flush each one.
Remember to flush in both directions until flush solvents exiting the component
are clean.
This
illustration details the three different A/C hose assemblies (or lines) on
a typical auto A/C system. Remember that each one of these hoses will have
to be flushed before replacing your auto A/C Compressor. Flushing will remove
any debris that may have been scattered throughout the system.
Flushing and
cleaning the auto A/C system:
It
is virtually impossible to replace an A/C compressor without flushing the
system. The extent of flushing or cleaning is dependent on the amount of
contamination and debris left in the system after the failure.
As
an absolute minimum, the high side of the system should be flushed. That
would include the hose from the compressor to the condenser, the condenser,
and the hose from the condenser to the evaporator inlet. (Note: depending
on the condenser design and the amount of debris, the condenser may have
to be replaced). Receive driers or accumulators can NOT be flushed (by virtue
of their design). Additionally, never attempt to flush a compressor.
Flushing
is really cleaning the internal components of the A/C system. It's important
to use an approved A/C flush
that will not leave any residue in the system and will evaporate quickly.
Use caution when selecting your flushing compound. Many A/C Flushes on the
market use reclaimed solvents and chemicals that are not safe for the A/C
system. Flushing can be accomplished with either an
aerosol type flush
(which does not require a flush gun) or a
liquid pour type that
is used with a flush gun.
Either
type (aerosol or liquid) flush agent will work, however you must have access
to 'dry' compressed air or nitrogen to 'push' the flush solvent through the
system. Nitrogen is the preferred method because it is an inert gas and will
not introduce any moisture into the system. After flushing, it is strongly
recommended that an in-line
filter be installed in order to catch any debris that may be left in
the system.
Using
pressure (air or nitrogen) behind the flush solvent will push it through
the components (hoses, condenser, etc.) to remove both oil and debris. It's
important to repeat the flush process several times, in both directions,
until the flush solvent removed from the component is clear. Complete details
on Flushing the Auto
A/C System are available here.
SERVICE
Required: Flush the A/C system by disconnecting each component and
flushing it as an individual item. Flush in both directions using only approved
A/C system flushed.
In-Line Filters:
They're really almost
like insurance for your replacement A/C compressor!
By
now it should be pretty clear that any A/C compressor failure is cause for
a complete system clean up. That's fine, but you should also consider additional
'insurance' for your replacement compressor.
In-line
filters are typically installed in the liquid line (after the condenser;
before the evaporator). The best feature of in-line filters is that they
have a much larger filter surface area to catch and hold any
debris while still allowing refrigerant and oil to flow. This is important
because in countless cases, even after flushing a system several times, some
debris remains in the system (Usually in the A/C condenser because of
the long tube lengths and turns.) They are simple to install and don't require
any special tools! See the
A/C In-Line
Filter installation instructions for yourself!
SERVICE
Required: It is good practice to add an in-line filter to your A/C
system whenever replacing the compressor. It provides the added insurance
against any debris or contamination left in the system restriction flow and
causing another compressor failure.
Summary:
No
matter what the reason is for replacing your auto A/C compressor, remember
that there is a lot of other related work that has to be completed before
you install the replacement compressor. We hope that this information has
been helpful and we welcome your comments. Just
e-mail
us!
An Illustration
showing a typical Auto A/C System
More helpful information
and articles about auto A/C repair:
Diagnosing auto A/C
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Flushing A/C Systems
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Recharging
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Replacing
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the complete details and what's really required to do the job right!
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This was probably
one of the best books on recharging air conditioning that I have seen...
