Auto Service World
Feature   April 1, 2009   by David Halpert, Assistant Editor

Under Pressure With A/C Systems

Taking a look at air conditioning systems as we head into spring

What can be said about automotive air conditioning that has not been said before? The fact of the matter is A/C systems haven’t changed a whole lot since they became commonplace in cars nearly forty years ago. However, it never hurts to brush up on the basics as we head out of the fall/winter season and into the hot and humid weather of the spring and summer months.

When you stop and think about a car’s A/C system, it’s actually quite astounding. All it takes to receive cool air into passenger cabin is one simple push of a button. Air conditioners are also pretty reliable and it is rare for new vehicles to have problems with the A/C systems; and as the car ages, the system tends to work just fine, often for the lifetime of the vehicle.

Avoiding misdiagnosis

Because of their overall reliability, and the fact that a failed A/C system does not endanger vehicle’s normal operation, maintenance on the system is often not a part of a technician’s regular inspection/repair routine on a vehicle. Automotive air conditioner experts say this reality often has technicians falling into certain routines and habits when problems do arise, ones that can cause even an experienced technician to misdiagnose the situation.

For example, take this situation: A car comes into the shop and the owner says, “My air conditioning isn’t working.” Now, a technician might do a quick inspection and say “You need a compressor,” because the head pressure is either too high or is on the low side.

“But in fact, the problem in a lot of cases is the condenser fan,” says Warren Willingham, owner of A/C Source (,a supplier of A/C systems and related components operating out of Phoenix, Arizona. “If that fan quits working, then the head pressure on the compressor in the system will go up. Until it blows, it starts to blow warmer air because the pressure’s too high. A lot of technicians don’t understand that it’s not a compressor.”

With over 35 years in the business, Willingham knows a thing or two about air conditioning systems, both on the supply side and the service side of the business, having operated a service centre of his own for more than a decade.

“The key to all of it is diagnosis,” he says. “The biggest problem is a lot of systems are diagnosed incorrectly. And it starts with gauges and knowing what to look for. A lot of people that work on vehicles start guessing because they don’t know how to use them properly. It all depends on the guy diagnosing it and getting [the diagnosis] right.”

He goes on to recall one such instance of a misdiagnosis that could have cost a customer an unnecessary outlay of money. Willingham had a friend who was visiting from Mexico and was experiencing problems with his car’s air conditioning. Taking it into a shop, he was given a US$1,500 estimate on what was first believed to be a faulty compressor. Offering to give it a look, Willingham soon discovered that a wire had detached from the compressor’s terminal inside the boot and out of view. It was this faulty connection that was causing the problems with the air conditioning, but which was mistakenly diagnosed as being a problem with the compressor itself.

We all know there is no one-design-fits-all A/C system across all vehicle makes and models. Each OEM is designed to their own specs. As a result, Willingham warns about the hidden details of A/C system that can lead to a misdiagnosis.

“The radiator and cooling fans are on the front,” he says. “Cars that have electric fans will have a radiator fan or a radiator fan and a condenser fan. Hondas are famous for having two fans where one’s hidden. Oftentimes, they’ll check to see the fan is working without having checked the one that’s hidden underneath.”

Also, keep in mind that in warmer weather the ambient temperature inside a garage is usually cooler than it is outside the garage, which plays a factor when diagnosing A/C systems.

“On a hot day you have to account for different pressures underhood,” he adds. “The hotter it gets, the higher pres- sures will go because the gas is getting hot and it’s trying to release all this heat from inside the cab. You have to watch your gauges to account for how hot it is outside and what kind of load you have on it. If it’s 70 degrees your gauge will show 70 and if it’s 100 degrees it’ll show higher. Refrigerant is also relative to the outside ambient temperature. So, again, it’s harder to diagnose.”

How to prevent comebacks

“What I’m finding with A/C components is they’re actually starting to last a lot longer,” says Steve Perusits, owner of Wally Clayson’s Master Mechanic Auto Service in Toronto, Ont. “You can actually see the technology change as the vehicles get newer and newer.”

Comebacks are an especially contentious issue with air conditioners and their repair. While no customer enjoys returning to a garage for a repair that should have been done right the first time, there’s nothing more frustrating than not receiving cool air on a sweltering day once your car hits the asphalt. Some people who do a lot of highway driving in winter are surprised to find their air conditioners not functioning once spring rolls around.

“Usually your air conditioner should run up to snuff when you put it to bed in the fall. However, the air conditioning’s condenser is right out front behind the grille,” continues Perusits, “There’s no guarantee it’s going to work come next spring because it’s possible a stone could come up and hit the condenser [as a result of highway driving]. While everything else is more or less hidden, if you do puncture a hole in the condenser what it does is basically shuts down the system because they are switches incorporated in there to make the compressor shut down if it detects a problem.”

Difficulties with air conditioners are likely one of two things: either there’s insufficient cool air coming through the vents or there’s no air at all. If you’re working on an older car and its A/C system doesn’t seem to be working properly, here are some general troubleshooting tips the experts recommend to keep in mind.

The air-conditioning of a car is (with the exception of the serpentine belt) an enclosed system made up of six parts: the compressor, condenser, receiver-drier, thermostatic expansion valve, the evaporator, and, of course, the refrigerant. If one part fails or is sluggish, the A/C won’t work properly. It also means there are only a limited number of components to check if the problem persists.

If there’s no cool air felt from the air vents it means a component is loose, broken, defective, or blown. A leaking component in the A/C system or in one of the A/C lines, hoses, or seals can also result is no air flow.

Now an insufficient cool air flow is harder to pinpoint, but not. Unless there’s a low refrigerant charge, your lack of cool air is the result of a loose drive belt, slipping compressor clutch, clogged condenser or evaporator, a slow leak in the system or a partially clogged filter or expansion valve.

“Back when there was R12 all you had to check for were oil stains,” continues Perusits. “Now with the R134 you can’t see any of the leaks. All you can do is to listen for the compressor and while it may sound okay, it may be broken internally. So you would have to put some gauges onto the system to see what’s happening pressure-wise.”

When a problem surfaces, a lot of the time it’s never just one leak, or one component that’s the cause. Oftentimes there is more than one leak or one defective part that puts strain on the entire system.

Tips For Your Customers

Two traits that a customer looks for when choosing their service centre are honesty and quality of services provided. To that end Warren Willingham of the A/C Source offered these tips to give to your customers to make sure their air conditioning systems run properly without a need for more service.

1. Don’t leave your vehicle idling with the A/C
running longer than necessary. This runs up head pressure and can cause hoses to blow or compressors to lock up. This will usually happen when the temperature is very high. Just use common sense and you’ll be fine.

2. Always keep your unit in the max (re-circulate) mode when the temperature is high. Thirty-degrees is a good guideline. In the normal mode you are trying to cool down the hot air from outside. It is okay to put it on normal for the first minute or two because the outside air at that time is cooler than the air inside, but change it to max (re-circ) as soon as it feels a little cool. In max mode you are cooling the cool air from inside the vehicle and the system doesn’t have to work as hard. Also, remember that the lower the fan speed, the colder the air from the vent.

3. The human body feels the difference in coolness of the air when it changes approximately 2.5-to three-degrees. If your air conditioner has warmed up enough for you to notice it, it is a good practice to shut it off. This has saved many compressor replacements and a slight inconvenience that could save hundreds of dollars.

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