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Considering A/C systems when searching for a new vehicle

Tuesday, May 1, 2018 - 07:00
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I can remember back many years when you could buy a new car without a heater — yes, a heater was an option way back when. There used to be ads on the radio highlighting cars that came with a radio, heater and white sidewall tires. This was back in the '50s, and I must say that many things have changed when it comes to purchasing a new vehicle. So why upgrade to a new vehicle? Is your daily driver doing its job, or does it need to be replaced? 

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When you stop and think about a car, the basic reason for having one is for transportation. Some people’s idea of basic transportation is different than others. Speaking from my own perspective, I like my daily transportation to be comfortable and quiet, have good handling characteristics, be dependable and get fair fuel economy. I also want a vehicle that I don’t have to be working on all the time. After all, I work on cars and trucks every day, why would I want to have my personal ride in the shop for anything but normal service?  

This 2017 Audi Q5 is powered with a 2.0 turbocharged engine. The powertrain uses an automatic transmission and an all-wheel drive system. The vehicle shows only 9,500 miles on the odometer.

When it comes to the basics of a vehicle today, not much has changed in the last 30 years. They still have a power plant, drivetrain, a steering system and a braking system. How these components are controlled has changed, along with the creature comforts of the vehicle. I like to be able to take a drive in hot weather and be cool and comfortable when I reach my destination.  

This brings us to the question of a vehicle upgrade, possibly a new vehicle. Any time I walk through a dealership to get to their parts department, I will look at the new wheels they have sitting on the lot or the showroom, and wow, they want some real money for these vehicles. I guess I am a little spoiled; the last new car I bought at a dealership was in 1990, and since then the cars I have had were cars my customers didn’t want anymore. All it took was a little repair and service and I could have a good quality car for a few dollars. One of these cars was a 1983 Peugeot 505 Turbo diesel. Yes, I must use the words “dependable and good quality” quite loosely, but I did enjoy that car. One big problem though — my wife hated that car.  

For many years, vehicles have been equipped with A/C systems that work very well and are very reliable. Add some electronic gadgets to the A/C system, and you can call it a climate control system, or HVAC system for short (heating, ventilation and A/C). I think I can safely say that most of us either have owned or do own vehicles with both the manual and automatic A/C systems. I do enjoy the vehicles I have with automatic HVAC systems, since I can get in the vehicle and drive and not have to keep fiddling with the room temperature or the fan speed. Aah, creature comforts at their finest.  

Research on new vehicles 
I have spent some time researching some things about buying a new vehicle. Once you get past the sticker shock of the price of this computer on four wheels, there are some things to consider. When you sign on the dotted line for the new ride, the value of that vehicle has just gone down by 11 percent. Let’s say you have just plunked down $38,000 for the new ride; it now lost $4,180. After the first year, the value has gone down 25 percent, to $28,500. You just took a $9,500 hit on the value of the vehicle.  

Figure 1 - Insurance company report on the cost of insurance comparing a 2011 Audi Q5 with a 2018 Audi Q5. The new car is actually cheaper to insure than the older model.

When it comes to insuring the new vehicle, there is some good news. The new vehicle, with its active cruise and collision avoidance system, is actually cheaper to insure than its older counterpart (Figure 1). My insurance agent did the calculations and came up with a mere $69 difference, but anything helps.  

Comparing vehicle A/C systems I’ve owned 
I own several vehicles. One is a 2001 Ford Ranger pickup. This is a very reliable vehicle, even with the odometer showing upwards of 270,000 miles. The A/C system is the basic CCOT (Clutch Cycling Orifice Tube) system. This is also reliable, which produces an ample amount of cold air, even on a very hot day. The A/C system is basic and consists of an evaporator core, high and low pressure lines with a fixed orifice tube, an accumulator, a condenser and a compressor. The electrical controls are about as simple as it gets. The only function the Powertrain Control Module (PCM) has is to control the magnetic clutch on the compressor. There are no bidirectional controls from a scan tool and all the blend doors and mode doors are either vacuum operated or mechanical. Any testing on this system must be done with a volt meter, a vacuum gauge or by watching things happen.  

Figure 2 - AC wiring diagram for my 2001 Ranger pickup. The wiring diagram shows the simplicity of the system. Is it easier to fix than the Audi that is discussed?

The next car is a 2011 Audi Q5. This is a nice comfortable riding vehicle with a very good A/C system. In this vehicle are many creature comforts (fancy A/C system and electronic gadgets). This vehicle has an automatic HVAC (heating, ventilation, A/C system), which pretty much takes care of itself when it comes to keeping the passenger compartment either warm or cool.  

Looking at the wiring diagram of this system shows it has seven different temperature sensors in the A/C system. It also has 10 different electric motors that control air flaps in the HVAC system. The system is controlled with a climate control module, which is on one of the data busses. Since this system is on the communication network, there is a lot of information available on the scan tool, not only diagnostic information, but bidirectional controls of most of the functions of the HVAC system. I find great value in the ability to command things with a scan tool and be able to either see the component move on scan data, or be able to hear, see and feel it operate.  

This HVAC system is much more complicated than the 2001 Ranger, although it has the same job, to keep the passenger cabin warm or cool to the desire of the passengers. Now, this Audi has one more feature the Ranger doesn’t — it has dual zone HVAC. With this vehicle I can stay warm, even if my wife wants the cabin cooled off. All she has to do is to adjust the temperature on her side of the car to her preference. This feature is nice, although it adds a lot of difficulty to the repair and service of the A/C system.  

The 2017 Audi Q5 is an early production 2017 vehicle. It is powered by the 2.0 turbocharged engine, with automatic transmission. This is an AWD (All Wheel Drive) vehicle with 9,500 miles on the odometer.  

This vehicle is much like the 2011, except for the collision avoidance and blind spot detection system. When it comes to the A/C system, it is close to identical to the older 2011. This particular vehicle was the last of the production with R134A refrigerant. The late production 2017 Q5 came from the factory with R1234YF refrigerant in its veins.  

Most new car warranties are pretty good when it comes to getting a problem fixed. Now when it comes to damage of something like the A/C system, because of something other than a manufacturing defect, the system should be repaired to its original condition to keep the warranty in effect. Whether people are aware of it or not, when a new car is purchased, they are paying for the warranty the manufacturers put on the vehicle. You might think of it as paying forward for things that might happen on your newly purchased vehicle. When doing a repair to a vehicle, finishing off the job to make it look like the vehicle has never been worked on has its benefits.  

More on the 2017 Q5 
This vehicle is one of the few brand new vehicles I see in my shop for regular service. Any time something new comes to the shop, I always like to take a close look at the vehicle to see what the vehicle manufacturers have done with the new models. This HVAC system bears a lot of resemblances to a lot of the Ford and GM vehicles I see, in that the system is controlled by a module that is on a data bus and most of the initial diagnosis of a problem can be done from the front seat with a scan tool.  

Figure 3 - Scan data screen dump of the many modules on the current model Audi Q5. It is easy to get lost in this system without knowing where you are going.
Figure 4 - Scan tool bidirectional controls screen for the AC system. This is where you go to command the different functions of the AC system. It's a great way to verify proper operation of the different components.

By using a scan tool, it is easy to see what kind of “creature comforts” are on this vehicle (Figure 3). Listed in the scan data are all the modules that could be on the vehicle. In the case of this Audi Q5, all the listed modules were not installed on the vehicle. Whatever it is, its a lot different than the 2001 Ranger with the manual HVAC system. When it comes to getting a direction on a problem with the HVAC system, the direction can most times be found with a scan tool. Figure 4 is a scan tool screen shot of the bidirectional controls for the HVAC system on this Audi. Under the hood, the system is laid out well, with easy access to most service items (Figure 5). The A/C label shows the system is still using R134A (Figure 6). 

Figure 5 - Underhood view of the engine. There is a lot of room to work on this vehicle, and most of the service items are easy to access.
Figure 6 - The AC label is easy to find and shows this vehicle has R134A running in its veins.

A broken Audi 
It wasn’t long ago I was called to a body shop for an A/C problem on a similar 2017 Audi Q5. The vehicle had hit another car in the rear and had extensive front end damage. The condenser, compressor and several of the A/C lines had been replaced and the system wouldn’t work after the repairs. At this point, I was called in to see what the problem was. Before any testing is done, I always need to know what flavor of A/C system the vehicle is using. This is especially true when working on VW-Audi vehicles. This vehicle has the Climatronic Comfort system. 

On any A/C problem the first thing I want to know is if there is enough refrigerant in the system to at least get the compressor to operate. After verifying correct pressure, it was time to get a scan tool hooked up to see if there is any information stored in any module on the vehicle that might be of interest.  

A full module scan was performed and as usual with any body shop vehicle, there were all sorts of circuit codes for lights. All the diagnostic trouble code information was stored and then all the DTC’s were cleared to see if the A/C system would go back to working. This did not fix the problem, so now it's time to get to work and find out why. On the second module scan I found three DTC’s stored in the A/C control module. Fault codes 00457, 00256 and 01592 are stored in the fault memory of the A/C control module and now that I have a direction, its time to find where the problem is.  

A little research into the problem, I found 00256 was for the G395 sensor A/C pressure temp sensor which is in behind the grille and is screwed into the A/C condenser. The 00457 is a network fault for J519, which is the body control module and the 01592 is for the air quality sensor, which is located in the A/C evaporator box. At this point, I want to do something easy, these two sensors are behind plastic things and the heater box is not easy to get to. I opt for a look at scan data. By using the scan tool and accessing data block 054 in the HVAC module, I found the ambient temperature was -40F and the A/C pressure did not match what I had observed on the pressure gauges. This is a good thing, since this sensor is the easiest to access.  

The next step is to get a wiring diagram of the system. A tip about working on VAG vehicles, the color wiring diagrams give a very good overview, but when you want pinpoint information, use the VW factory track diagrams. Many times the information found on these diagrams is priceless. The wiring diagram (Figure 7) shows both the G395 sensor and the G238 sensor have a common ground at the 639 ground connector that is on the left A pillar. One thing I have found about sensors like this used on VW vehicles, they might look like any common two- or three-wire sensor, but most are not like the sensors used on Ford or GM vehicles.  Don’t try using a jumper wire on these sensors! That can get expensive. This G395 sensor has a power and ground and a network wire that goes to the vehicle electric control module (body control module if it were American iron).  

Figure 7 - Factory wiring diagram of the G395 & the G238 sensors. There is a lot of important information about the electrical system found with this diagram.

Electrical basics say for this module to work, it needs a power and ground and network communications. With the easy access to this sensor, it is easy to test by using a DVOM. My testing found there was no ground to the sensor, which would explain the readings I found on the scan tool. By using a wiring diagram of the grounding system in this vehicle, I can see there are many different electrical components that are grounded at the 639 ground location. By knowing this, it is easy to turn the key on and see if any of these different things are working. One thing that caught my eye was the wiper control module is grounded here. Turn the key on, turn the wipers on, the wipers work and yes, the ground point is intact and working.  

With the ground point proved out, its time to look for damage to the wiring at the front of the vehicle, where the damage was. Sure enough, about six inches from the G395 sensor, the harness had been crushed and the ground wire was broken. Fixing the wire brought the A/C system back to operation. Sometimes seemingly difficult problems can be quite easy to fix.  

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