By Jim Marotta
What was once a basic system to heat and cool the interior
of a vehicle has become a multi-zone, automatic temperature control system with
cabin air filtration. No longer are a few tools and some basic knowledge adequate
to diagnose and service modern climate control systems. Without proper tools
and up-to-date information, mistakes are inevitable.
Let's take a look at the eight most common mistakes techs
make when servicing climate control systems.
1. Not Identifying
the System Refrigerant
Do you know what type of refrigerant is in your A/C system? This
is important information because if you mix refrigerants, the system will not
function properly and the wrong refrigerant may damage
components. More importantly, if there are non-approved hydrocarbon
blend refrigerants in your A/C system, it could be explosive!
The only way to know what is in an A/C system or container
is to use a refrigerant identifier. Owning one also helps you to avoid damage
to your air conditioning service equipment from contaminated refrigerant and prevents
contamination of your refrigerant supply, warranty loss on recovery equipment, and
even risk of injury.
The identifier found contaminants in
the system and registered "FAIL," telling the tech to evacuate and replace the refrigerant.
2. Not Using the
The manufacturer of the vehicle or
A/C compressor designs each air conditioning system for a specific viscosity and
type of lubricant. While some aftermarket lubricant suppliers claim
their oils are universal for every application, these lubricants will usually
work best for one situation, but not nearly as well for others.
If you are servicing an older vehicle and CFC-12 is the
refrigerant, manufacturers specify the use of mineral oil as the lubricant. A vehicle
retrofitted for use with HFC-134a uses polyalkaline glycol (PAG) oil. For vehicles originally equipped with
HFC-134a use the OEM-specified viscosity PAG lubricant.
In general, manufacturers offer three viscosities, or
thicknesses, of PAG oil. The smaller number indicates less viscous oil. Many
Nippon-Denso style compressors use the 46 centistoke lubricant; this includes
many of the Ford and Chrysler compressors. Several import and aftermarket
compressors use the 100 centistoke lubricant. General Motors uses the 150 centistoke
lubricant primarily on the Delphi-Harrison compressors.
The manufacturer of the vehicle or compressor determines the viscosity and
lubricant type. While lubricant suppliers claim their oils are universal, each
lubricant will usually work best for one situation.
3. Improperly Recharging
Early A/C systems required large quantities of refrigerant; 3
lbs. or more was not uncommon. Charge tolerances for these systems were also
reasonable. A simple digital scale and charging station could easily handle the
Today most passenger cars and light duty trucks carry less
than 20 ounces of refrigerant, or just over 1 lb. One of the smallest capacity
systems on the market is the Toyota Yaris, which runs on approximately 11
ounces. With the accuracy of some older scales at plus or minus 0.2 lbs., or more
than 3 ounces, the possibility of over- or undercharging a system becomes a
Just 2 ounces of over- or undercharging reduces performance,
and 2 ounces of undercharging also affects compressor lubrication. For greater
accuracy, use a charging station certified to SAE International standard J2788.
Just 2 ounces of over- or undercharging reduces system performance,
and 2 ounces of undercharging also affects compressor lubrication. For greater
accuracy use a charging station certified to SAE standard J2788, such as the
4. Not Using
At present, there are only two OEM
recommended refrigerants; CFC-12 and HFC-134a, with a third to come
shortly. OEMs specify CFC-12 for use
in vehicles manufactured prior to 1992, when they changed to HFC-134a. Currently
HFC-134a is the only refrigerant automakers specify for use as a retrofit
refrigerant for CFC-12 vehicles. Automakers and compressor manufacturers design
current HFC-134a mobile A/C systems only for HFC-134a refrigerant and the specific
lubricant, polyalkaline glycol (PAG).
market a number of other refrigerants that contain hydrocarbon blends, the EPA does
not accept them. Beware of inexpensive
refrigerants being advertised as "Accepted." Use trustworthy brands.
Components with Incorrect Performance Specifications
In many cases when servicing an air conditioning system,
replacement parts are expensive and there's an incentive to save money by
purchasing inferior parts. In a typical expansion valve type air conditioning system,
refrigerant absorbs heat in the
evaporator. Afterwards, the refrigerant gives up the heat in the condenser and
the process continues in a cycle.
If either of these heat exchangers, or the radiator-the
third heat exchanger- does not match OEM specifications for performance, the
system will not operate properly. A part may look the same as the original and bolt in place
correctly, but that does not mean it meets OEM performance. Check the specs and
avoid the hassle.
6. Not Performing a
Thorough System Evacuation
Depending on the ambient temperature, many older
recovery/recycling machines in operation today may only recover 50% of the
refrigerant from a system. Even the best machines that far exceed the old SAE
J2210 standard requirements may leave up to 30% of the refrigerant behind.
Here is an example: In a system with a 16-oz capacity and 12
ounces remaining in the system, you might unknowingly recover only half the
charge. That leaves six ounces of refrigerant remaining in the system. When you
recharge the system with 15 oz. of fresh refrigerant, the system will have 21 ounces
and be overcharged by 38%.
Fortunately, if you purchased a recovery/recycle machine
that conforms to the SAE J2788 standard, you will recover 95% of the
refrigerant. Testing also indicates that these new machines' more powerful
compressors draw down to far deeper vacuums.
If you are using any older
recovery/recycling machine to evacuate the A/C system, it may only recover 50%
of the refrigerant, while newer machines recover 95%.
7. Improperly Flushing the System
When any mechanical component of the system has a
catastrophic failure, debris may spread throughout the refrigerant loop. Flushing to remove debris that could cause failure of the
replacement compressor and to remove debris that could impede refrigerant flow through
the condenser is only natural. But flush with the wrong product or use the
wrong procedure and you could do more harm than good.
Once again, this is the time to follow the manufacturer's
recommendations, which can vary considerably. For example, General Motors
recommends flushing with liquid refrigerant, while Ford recommends a liquid
flushing solvent. Both manufacturers also recommend using a closed loop
While the flushing agent may be different,
flushing with a closed loop flushing machine is the best method for removing
all debris from the system.
8. Not Checking
Depending on when you make a repair, the owner might not use
the system again for months. If a small leak exists, the system might operate
well right after repairs, but not months later. Refrigerant
escapes easily from small leaks in a damaged system, and it's not always
easy to notice the leak. Electronic leak detectors can find leaks
effectively and are one of the most efficient ways to check your repairs or deal
with a problem leak.
Since the EPA tightly regulates gas release and can fine violators
heavily, performing a proper leak inspection after making repairs is advisable.
Refrigerant escapes easily from
small leaks in a damaged system, and the evidence of the leak isn't always easy
to notice. Electronic leak detectors can find leaks efficiently.
Make sure you have the information you need to avoid A/C
service mistakes. A subscription to ChiltonPRO,
with comprehensive service information and capacity specifications, will give
you all the information you need to keep an A/C system in top shape for the
A muscle car enthusiast and drag racer, Jim Marotta is a freelance automotive writer with more than 20 years experience in the automotive industry.