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Take steps be sure HVAC costs don’t get out of hand

By on July 2, 2014

Trucks manufactured in the ’80s and ’90s had a very simple A/C system, typically consisting of a single wire from the A/C control switch in the dash to a thermostat, then on through a pressure switch and finally to the A/C clutch. Now, computers have improved the efficiency and effectiveness of Heating Ventilation Air Condition (HVAC) systems, while also making them far more complex.

So while drivers do end up getting more out of a well-functioning A/C system, the advanced technology that makes that happen also substantially drives up the cost of service and repair. Drivers must take preventative measures to avoid unnecessary spending.

Compressor communication

One of the great advances in modern A/C systems is the fact that the operator has far more control over the climate inside the vehicle, with an ability to fine-tune the temperature by a few degrees. That temperature is checked and adjusted by an A/C-dedicated computer that also monitors duct temperature, refrigerant pressure, engine RPM, heater core temperature and so much more.

The A/C computer communicates with multiple other microprocessors on the vehicle to tell the A/C compressor clutch to engage or disengage when necessary. For example, the A/C computer knows when the blower motor is not turning and will turn off the A/C compressor until it sees RPM on the blower motor. That keeps the A/C from freezing up, which could cause the compressor to fail.

The truck’s computers work hard to prevent failure, but problems do still occur and need attention when they do. But it’s not a matter of getting a mechanically inclined pal to take a look and help replace a part. A technician must have the proper training to understand all of the components and how they control the A/C system. A diagnostic computer is necessary to evaluate trouble codes and functionality of each component. The key to minimizing vehicle downtime is to use a truck service network that trains their technicians to properly repair these complex vehicles.

Condenser confusion

The A/C condenser has also seen radical changes over the past 15 years. Previous condensers used a serpentine design. There was a single tube from top to bottom that sort of snaked from side to side. The new condensers use a parallel flow design, with the refrigerant moving across the condenser through several small passages at one time. This makes the new condensers 25 percent more efficient, which makes up for modern refrigerants that can be less effective than the older R12 refrigerants. The downside to these newer condensers is the difficulty of cleaning them in the event of a catastrophic compressor failure. It is practically impossible to clean them with normal shop A/C machines. That means that the condenser requires replacement in the event of a major A/C compressor failure, which means that the cost to repair an A/C system will be higher.

With predictions of brutal heat this summer, working A/C is not a mere luxury. Getting the proper maintenance performed on a vehicle seriously lessens the risk of paying the price of a failed system. And the proper maintenance is very easy.

Replace the cabin filter per the manufacturers’ recommendation, or when needed. All refrigerant leaks must be located and repaired in a timely manner to avoid the compressor heating up and eventually failing. These two simple maintenance procedures can save you time, money and a lot of sweat.

Homer Hogg, Technical Training Manager for TA and Petro, has worked as a truck technician for
more than 30 years. He is ASE Master-certified, a Daimler Certified Trainer and a member of the Nashville Auto Diesel College Hall of Fame.

Homer Hogg’s “Maintenance Matters” airs on the Dave Nemo Show (Road Dog Trucking, SiriusXM 128), 8 a.m. ET, the first and third Thursday of each month.

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