News Maintenance

Servicing Today’s A/C Systems

Changes Come in Details of Modern Vehicles

Order Reprints

An electric fan clutch assembly used on a 6.7L diesel engine.


During the past three or four decades, the basic theory of the automotive air conditioning system hasn’t changed a whole lot. What has changed is everything else that’s part of a vehicle’s air conditioning system. 

As we know the refrigerant has changed from R12 to R134a and now to R1234YF. These changes were made mainly as an environmental change. Besides the refrigerant change, the air conditioning systems have become more efficient and compact. The refrigerant capacity has grown smaller and the components have become smaller, as well. One reason is that the engine bays have decreased in size in order to fit all the various components, plumbing, and wiring harnesses closer together. Servicing these modern air conditioning systems can increase labor costs to your customers due to the complexities and tight access it takes to reach these components. Along with the increased changes in the systems themselves, other changes like tooling and training have become a necessity to be able to keep up. Just like any other automotive system, it’s important to be able to stay on top of these changes so not only can you stay competitive but also profitable.

As I stated earlier, the theory of automotive air conditioning systems still operates based on pressures of temperature, which hasn’t changed. In this article, we will look at some of the service techniques and procedures of working on modern air conditioning systems. Some of you have probably started seeing the R1234YF systems come into your service bays. Many of these systems may or may not still be under the manufacturer’s warranty. As you start seeing these systems more and more, an investment will need to be made in updated equipment, tooling and training. But this isn’t any different than what we’ve run into before with other automotive systems … correct? 

Today, as we drive our vehicles, 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. The modern air conditioning system is controlled by a computer system. Most vehicles have an HVAC controller or control module. The HVAC controller which monitors its three subsystems of heating, cooling, and air conditioning work in tandem to make sure that customers have the utmost control over the climate of their cabin and are provided with clean air via ventilation.

Monitoring a system of multiple sensors helps the vehicle’s central processing unit relay diagnostic information to the dashboard display. The other functions of HVAC systems in vehicles include a thermostat regulating temperature, and sensors that control moisture and humidity values in your vehicle’s cabin. Other common features include thermal systems control, seat- and location-specific heating and cooling, and automatic defrost settings utilizing fogging sensors. With all of these electronic add-ons, it’s important to have a capable scan tool that’s up to date.


These systems are no different than any other systems on the vehicle as they have to be diagnosed in a similar fashion. Sometimes a simple fix is just a software update to the control module. When using the new R1234YF refrigerant it’s important to follow the new procedures and guidelines that are put in place during service. For example, R1234YF is a new environmentally friendly refrigerant that has a 99.7% lower Global Warming Potential (GWP) than R134a. The new refrigerant is considered mildly flammable and has thermodynamic properties similar to R134a. Technicians must only use a SAE J2913 certified electronic leak detector when checking for leaks in an R1234YF A/C refrigerant system. Other, non–certified leak detection devices could serve as ignition sources in the presence of hydrocarbons or other flammable refrigerants. Other leak detection practices for R1234YF involve the use of a leak detection pump.

The R1234YF systems require the use of new, specific A/C compressor oils. The new refrigerant type uses ND-oil 12, which is actually a PAG 46 oil but with additives specifically for the R1234YF type refrigerant. One of the most critical things to remember when servicing a newer HVAC system is the equipment used to service these systems are totally different than their predecessors and the equipment is not to be shared, as cross-contamination will occur. Refrigerant recycle and recovery machines are separate and different all together. There are some manufacturers that have a dual purpose machine like the CPS products FX3030, which can recover, recycle and recharge both R134a and R1234YF refrigerants.

Although the refrigerant capacities don’t seem to be that much different from one another, the cost per ounce of R1234YF is substantially higher. Cost can be about $10 per ounce. These systems are very expensive to repair so maintaining the vehicle is critical. There really aren’t any differences as to the way you service the R1234YF systems as opposed to the R134a vehicles. The components are basically the same. Certification is a must. The EPA made it mandatory that after January 2018 a Section 609 certification card will be required to purchase R-12, R134a, or R1234YF cylinders of two pounds or more. Distributors will be required to keep records of certified technicians purchasing refrigerants. 


When servicing a modern HVAC system, there are several components that need to be taken into consideration for proper operation to occur. The most important test you can perform on an HVAC system is a detailed visual inspection. Sometimes just a visual inspection will reveal the culprit right away. It doesn’t matter where you start your testing, but it’s important to cover all bases.

Let’s start with the vehicle’s cooling system. The vehicle’s cooling system needs to be functioning the way it was designed. A cooling system that’s not functioning properly will affect the operation of the HVAC system. Having the proper antifreeze along with the correct ratio of the antifreeze to water balance will keep the engine not only cooling better, but the correct concentrate will prevent components from corrosion and premature wear. 

The components to check would be the water pump for leaks, pulley defects, bearing failure and proper coolant flow. Other components that work with the water pump assembly are clutch fans, fan blades and the fan shrouds as well. What do these issues have to do with the HVAC system? If the fan clutch isn’t working correctly to increase the fan speed, that’s needed to cool the refrigerant down as the high side refrigerant pressures start to rise in the condenser, then the high side pressure switch will alert the HVAC controller to shut the compressor down to prevent the refrigerant from boiling, which would significantly decrease the performance of the air conditioning system. The same goes for the electric fan module, as well. Fan belts such as a serpentine belt or v-belt need to be in good shape with the correct tension applied. A belt that’s loose, glazed or damaged will affect not only the cooling system but the air compressor, as well. The engine’s pulleys need to be free from dirt, debris and any irregularities that might impede operation. A chip in the pulley will cause premature belt wear as the belt will rub against the chip and start shredding the belt little by little. A good visual inspection is critical in stopping future belt failures. 

Pulley alignment is critical as well. Using a belt/pulley alignment tool will aid in checking for proper alignment. When performing your visual inspection of the air conditioning system, be sure to be on the lookout for any oil residue on the fittings and connections which would indicate a possible leak in the system. When you are performing your leak check of the system, use your electronic leak detector and circle around the whole fitting or area where you see the oil residue. Hold the detector about a quarter of an inch away from the area to be tested. It is important that there isn’t any wind, fans running or any chemical odors near the leak area as that will throw off the testing. After you have performed your checks under the hood, don’t forget to check out the inside of the vehicle. Before you check the controls that operate the climate control settings take a good look at your windows.

Yes, I did say windows.

Check to make sure they roll up and down and when they are up check to make sure they seal correctly. Any window that doesn’t seal will let some of the desired temperature that is in the vehicle out. Using a smoke machine, you will be able to detect any sealing issues as the smoke will exit the vehicle. Also check the doors as they need to close and seal properly as well. Any leaks in these areas will decrease the performance of the HVAC system. Next check the controls of the climate control panel. Make sure all buttons work and that each selection is giving the desired results. Buttons, LED displays and manual sliding controls will wear over time. Using a scan tool on the newer systems will allow you to run the actuators in their full ranges. Some scan tools will let you calibrate the actuators, if needed.

Many manufacturers make it mandatory to perform a calibration test after installing a new actuator. That is why having a capable scan tool is so important these days. Another thing that you will want to do on older systems that work off of the vehicle’s vacuum supply is to listen for a vacuum leak. If you hear one but can’t see it then using the smoke machine on the system will reveal where your leak is coming from. Don’t forget to check the controls for the rear seating. Some vehicles have auxiliary controls that control temperature and blower functions. One last thing I would like to mention for vehicles that have a lot of the high-end options would be to check the operation of heating and cooling seats. These, too, are part of the vehicle’s creature comfort amenities that also adds in the overall comfort of the vehicle owners.

These are just some of the items that need to be checked while servicing the vehicle’s HVAC system. The important thing to remember is to pay attention to the details and don’t overlook the obvious. The way I go about diagnosing an HVAC system is, as I mentioned earlier, is to perform a complete visual inspection before I even attempt to hook up a set of gauges or even a scan tool. Your diagnostic approach may be different than mine, but the end result needs to be the same. Fixing the customer’s vehicles right the first time will not only keep them cool but will keep them coming back should they need your services at a later date. Repeat customers is what we all strive for. Having the proper training, top notch equipment and a logical diagnostic approach will keep your service bays full and your customers coming back. 

Related Articles

Electronic/adaptive ride control: A brief overview of today’s systems

Servicing Air Condition Systems

Electronic air conditioning -- An overview of systems found in today's hybrid vehicles

You must login or register in order to post a comment.