Understanding your car’s HVAC system could save you money
Vehicle HVAC systems keep us comfy and keep our windows clear when they work, but when things go awry it can turn an easy commute or tour into a nightmare. Knowing what’s behind the dash and how it works and what can go wrong may go a long way to saving some repair dollars, sweat, and/or chills.
Your ride’s HVAC unit is basically a compact furnace/AC device and functions a lot like your home system, minus any open fuel combustion. Picture a long rectangular black plastic box just slightly shorter than the width of your auto’s dash with rounded edges and a few bulges and you’ve got a pretty accurate idea of what a vehicle’s heater box looks like. It contains an electric fan with a circular hamster-cage blade arrangement to move air, a heater core that contains hot engine coolant for heat, an air-conditioning evaporator core (when equipped) for cold air, and a series of vents, ducts, and control doors and valves to change air flow to various outlets in the cabin and to adjust temperature. Very few parts of it are easily removed for repair or replacement without having to first take out the dash and the floor console.
Blower-motor failures and noises are common concerns across just about every vehicle line. If a blower motor stops working on one or two speeds only, but continues to operate on the highest or higher speeds, the fault most likely lies in its regulator. These electronic devices vary the voltage fed to the motor, reducing or increasing its speed on demand from the control switch. Most carmakers make the resistor easily accessed by tipping the glove box bin all the way out of its dash location. The resistor will then be visible, mounted on the side of the heater-box, near where the blower motor is housed. Resistors can be sourced from authorized dealerships or from aftermarket parts stores for common models. This is a task that most DIY types will tackle.
Squeaky blower motors can drive even the most sedate operator around the bend and are caused either by failed motor shaft bearings or debris trapped in the cage-fan unit. The types of noise each create are unique and easily identifiable. On many vehicles, a blower motor can be accessed without full heater-box removal (like the resistor, usually located behind the glove box). If dealing with a debris noise, sometimes a small flexible attachment on a vacuum cleaner can be used to remove the offending material without completely taking out the blower itself. If you need a replacement blower, as with resistors, you may find better pricing if you shop around.
Internal air-directing door failures can be real headaches because, depending on the fault, they can prevent air flow from getting to where you need and want it, or change the cabin temperature to unbearable levels. Many automakers now use small electric servos to do these jobs rather than the cable or vacuum systems of yesteryear.
Most systems use three or more of these units (mostly interchangeably) and few are accessible without stripping out the dash or using some contortionist moves while working in the dark. Check first — before trying to remove one — to see if there are any software updates for the control system.