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 Specified Lubricant

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 Systems

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 service.

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 definite possibility.

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 one shown.


4. Not Using Approved Refrigerants

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).

Although companies 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.


5. Using 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 flushing machine.

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 for Leaks

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 warm weather.


A muscle car enthusiast and drag racer, Jim Marotta is a freelance automotive writer with more than 20 years experience in the automotive industry.