Is Your Car Suffering From One Of These 3 HVAC Electrical Faults?

Automotive Blog

Spring can be a season filled with wild temperature fluctuations, and that means you may be reaching for your air conditioning one day and your heater the next. Unfortunately, it's also the time when many people notice problems with their vehicle's air conditioning system. While automotive AC issues often have mechanical causes, electrical faults are sometimes to blame.

If your car's air conditioning system doesn't seem to be working as it should, it may be due to a failure in one of these three essential electrical components.

1. Bad Blower Motor Resistor

Your blower motor resistor, which some manufacturers refer to as the final stage resistor, is the component that allows your car's fan to blow at varying speeds. You're probably aware that a typical home HVAC system always operates at full speed, but a fan blowing at maximum power is significantly less pleasant in a vehicle.

Manufacturers typically install a resistor before the blower motor to solve this problem. Your car's HVAC controls vary the resistance in this component, altering how much power the blower receives. If your resistor is going bad, your AC may blow too little, too much, or not at all. You may also notice the fan speeds varying at random regardless of where you set the dial on your dash.

2. Faulty Low-Pressure Switch

The low-pressure switch is both a safety item and a critical part of your air conditioner's regular operation. This switch monitors the refrigerant pressure level in the system, preventing the compressor from operating when the refrigerant pressure is too low. Low refrigerant pressure can lead to slugging, ultimately damaging or even destroying your compressor.

A bad low-pressure switch will typically fail in the "safe" position. In other words, it will prevent your compressor from turning on. If you have a faulty low-pressure switch, you may get warm air from your vents, or your compressor may only run briefly before shutting down. A qualified AC repair shop can check and test your low-pressure switch to determine if it's causing your problem.

3. Blown Relay or Fuse

Checking the fuse whenever your AC doesn't work is always a good idea, but don't shove a new fuse in and call it a day. Fuses blow when there's an underlying electrical fault, so it's critical to determine why your fuse failed, especially if it keeps happening. The relay is another potential failure point. This component allows a low-voltage signal to switch on power to your air conditioning system. Unlike fuses, relays are mechanical switches that can wear out over time. The relay may work intermittently, providing cooling occasionally but failing to start the compressor at other times. Since relays are usually relatively easy to check, they are often one of the first things that a technician will examine when diagnosing an AC problem with your car.

For more information, contact a car AC service, like


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