HVAC system—a good start to the new season

The HVAC system: in summer we can’t do without it, and even in autumn it provides a valuable service on sunny days. In winter it provides dry air in the cabin and prevents windows from fogging up, but even the early days of spring remind us once again that the sun is powerful and the interior of a car can heat up very quickly. So we switch on the HVAC system without a second thought. Unfortunately, however, we often don’t get the spring breeze we’re hoping for. Instead, all we get is musty air.

Where does this bad smell come from?

Refrigerant circulates through the HVAC system in liquid form under high pressure. When the system is switched on, the refrigerant enters the evaporator. Because it has a lower pressure level, the highly pressurised refrigerant expands and transforms from a liquid into a gaseous state: it evaporates. This draws heat from the surrounding air. As a side effect, the air flowing into the interior of the car, which flows around the evaporator, cools down and flows into the cabin like a fresh breeze.

When warm air is cooled down, some of the water contained in it condenses. We all know this effect from bottled drinks. When they are taken out of the refrigerator in summer, the warm air around the bottle cools down. The water contained in the air then condenses on the bottle in the form of droplets. Water condenses on the evaporator in the same way. It flows off—and therefore forms a little puddle under the vehicle in summer—but some residue remains. If the HVAC system is switched on regularly, this is not a problem. New condensation water forms and washes away the old. If the HVAC system goes unused for a long period of time, a small moist biotope gradually develops in which foul-smelling bacteria can breed. When it is finally switched on again, this air is initially blown into the interior of the car. This is not only unpleasant to the nose but also a hazard to health—precisely because of these bacteria.

What can be done about it?

The best thing is to carry out an HVAC check. The repair shop checks the HVAC system for leak tightness, replaces the refrigerant if needed or tops it up, and changes the cabin air filter. The air channels and the evaporator are also disinfected, which is good both for the wallet and for the health. After all, a properly functioning HVAC system saves fuel. Preventive maintenance also costs less than a repair of the entire system.

MAHLE regularly receives awards from automobile manufacturers for its cabin air filters and provides replacement filters in original equipment quality to repair shops. MAHLE Aftermarket also provides the right repair shop equipment for the HVAC check, with HVAC service units for the refrigerant R-1234yf (MAHLE ArcticPro 200yf) and the ACxpert 1000a for the refrigerant R-134a.