Your car's air conditioning system uses several different fans to help keep you cool during the summer. Your interior blower performs a similar function to your home's air handler: it moves cold, dehumidified air away from the evaporator coil and into the cabin. It's easy to notice issues with your blower since you'll get inconsistent or weak air from your vents.
The air conditioning system also needs to transport warm away from the condenser coils, however. You can usually find your condenser coils at the front of the car, near the radiator. This position allows fresh air to blow over the coils and provides natural, efficient cooling. When you've stopped your vehicle or the load on your AC is exceptionally high, a secondary fan kicks in to provide extra condenser cooling.
Why Do You Need a Secondary Cooling Fan?
Some older vehicles use a single fan to cool both the radiator and condenser, but most modern cars have two separate fans. The secondary cooling fan provides maximum efficiency for your cabin air conditioning and your engine's cooling system. Since the cooling fan only blows on the condenser coils, you'll avoid overcooling your motor when you run your air conditioner.
The operation of this fan can vary significantly between makes and models. Some cars run their secondary cooling fans whenever the air conditioner turns on. Other manufacturers design their systems to use a pressure switch since a high load on the AC system can increase refrigerant pressure. In these cases, the fan only turns on when necessary to provide extra cooling for the condenser.
Symptoms of a Failing Cooling Fan
If your secondary cooling fan runs at all times, then there's a fairly obvious sign that it's faulty: it won't turn on. In most cases, the secondary cooling fan should engage anytime you turn your AC on in warm weather. You can leave your car idling with the air conditioner turned on for a few minutes to be sure, but there may be an issue if the fan never engages.
Your AC system relies on the condenser fan for proper operation, so you'll usually notice changes in your cabin cooling, as well. One common symptom is short cycling (the compressor turning on and off rapidly), which results from safeties kicking in to prevent overheating. You might also notice warm or humid air from the vents.
Your car's air conditioner requires a delicate balance of components to function correctly. A failing condenser fan can impact the refrigerant cycle, ultimately leading to damage in more expensive parts, such as your compressor. If you suspect a problem with your cooling fan, have your car evaluated by an auto AC repair service shop as soon as you can.