A/C Pro

#PopTheHood: A Dipstick’s Guide to Accessories

Your car’s engine obviously provides the power needed to move your vehicle down the road. But it also powers everything else in your car: the lights, stereo, steering, A/C system, windshield wipers—everything.

The engine provides power to these accessory systems through a collection of belt-driven parts bolted to its front and sides. It’s all those spinning things you see when you look under the hood: the engine powers a rubber belt, and the belt winds its way through various pulleys to turn each of the accessory parts.

A lot of parts means a lot of different things that can go wrong, though some of them are among the easy repairs that pretty much anyone can do. The key is to know what the parts are and what they do, so you can quickly tell which one has gone bad.

So, as part of our beginner’s “Pop The Hood” series, here’s a basic explanation of all those spinning parts on the front of the engine.

#PoptheHood | A Dipstick's Guide to Accessories | A/C Pro Blog

1. Alternator

What it is:  A small electrical generator that recharges the battery so it can run every electrical device in the car.

How to find it:  It is usually near the top of the engine, is usually silver-colored, and usually has metal ribs through which you can see copper wires. Some have a small fan attached to the front pulley. Electrical wires run from it to the battery.

What happens when it fails:  The car will slowly run out of electrical power as the battery is drained. You may not be able to start the car, or if the engine is already running, everything electrical will start to fade. Since a gasoline engine requires electric spark plugs to fire, the engine will start running rough, lose power, and eventually come to a stop.

How to fix it:  A bad alternator has to be replaced. Since the alternator is one of the easiest parts to get to and is held by just a couple of bolts, many people choose to do this repair themselves.

2. A/C Compressor

What it is:  A pump that compresses and pushes refrigerant through the air conditioning system.

How to find it:  It has a bigger pulley than the alternator, and the center of the pulley only spins when the A/C kicks on. Instead of big electrical wires like on the alternator, the A/C compressor will have two metal refrigerant tubes coming out of it.

What happens when it fails:  Your A/C will blow hot air, even when on the maximum cold setting. However, it’s important to note that hot air does not usually mean you need an expensive new compressor. A/C compressors are designed to only come on when there is enough refrigerant to compress. So, if your compressor is not running, that could be a sign that it is working as designed, and simply needs more refrigerant.

How to fix it:  First check the refrigerant pressure (such as with an A/C Pro gauge) and add refrigerant if needed. You’ll also need to fix the leak that caused the refrigerant problem and add compressor oil, but you can do all that automatically by using one can of A/C Pro. If the refrigerant pressure is correct and the compressor truly has gone bad, we would recommend taking it to a professional mechanic.

3. Power Steering Pump

What it is:  A hydraulic oil pump that puts the “power” in “power steering.” It pumps oil to the power steering cylinder, which controls the direction your front wheels are pointing.

How to find it:  It is the only one of the belt-driven parts to have an oil fill cap. The cap will usually be labeled “power steering fluid.”

What happens when it fails:  Your steering wheel will become very difficult to turn, especially when driving slowly or at a stop. You won’t lose steering completely, but you’ll have to provide all the power with your own two hands.

How to fix it:  Often the problem is low power steering fluid, which you can check with the cap and attached dipstick. As with the A/C system, low levels means there is a leak to be fixed. You can try adding a stop-leak power steering fluid; it’s a cheap fix and generally worth a try. If the fluid continues to leak out, or the pump itself just isn’t working, you’ll need to get it replaced.

4. Water Pump

What it is:  A pump that circulates coolant (water + antifreeze) through the engine and radiator to keep the engine from overheating.

How to find it:  Good luck. Of the parts listed here, this is the most likely to be buried at the bottom of the engine compartment.

What happens when it fails:  Your engine will overheat. Or, before that, you may see green- or yellow-colored water leaking out.

How to fix it:  A bad water pump will usually need to be replaced by someone who knows what they are doing. In other words, go see a mechanic.

5. Radiator Fan

What it is:  A circular fan that pulls air through the radiator (and the A/C condenser) to cool the car.

How to find it:  It will be right up against the back of the radiator, and covered with a shroud (as in the photo above). Some fans are belt-driven, but others are powered by a separate electric motor.

What happens when it fails:  Your engine will overheat. This will happen much more quickly if you are driving slowly or idling at a stop; if you are driving at highway speeds, air will still be blowing through the radiator.

How to fix it:  The fan itself is unlikely to break. Usually, the problem is that the motor or belt that turns the fan is broken, or that a wire, fuse, or sensor has gone bad.

6. Serpentine Belt

What it is:  The rubber belt that transfers power to the accessory parts. On older vehicles, there may be more than one belt; these are called V-belts.

How to find it:  It wraps around the other parts listed here. If you can’t find it, that probably means it has broken and fallen off.

What happens when it fails:  All of the problems listed above happen at once. It’s not pretty.

How to fix it:  Replace it with a new belt, preferably before it breaks. To see how, check out our list of ridiculously easy car repairs you can do yourself.


Hopefully this has helped you become a better-educated driver, and will help save you some confusion and money down the road. For more in this series, check out our blog listing and follow us on Facebook or Twitter to find out about future posts.