You might think of your auto air conditioning system like the engine cooling system. Just as the engine cooling system moves heat from the engine to the air, the air conditioning system moves heat from the cabin to the outside. This makes for more comfortable driving and defogs your windshield faster, but how does it all work?
Auto Air Conditioning Components
Like the engine cooling system, the auto air conditioning system uses a pump to circulate coolant. Air conditioning refrigerant’s special property allows it to phase-change from liquid to gaseous forms. Phase changes come with another special property: the absorption and release of heat. Here’s a basic summary of how each part produces these phase changes and keeps the cabin cool.
Compressor: The air conditioning compressor, driven by a belt or electric motor, circulates refrigerant in the system. Compressed refrigerant moves through tubes and hoses to the drier and condenser.
Condenser: Usually mounted forward of the radiator, the condenser looks like a thinner radiator. Air rushes through the condenser and cools the refrigerant. When pressurized and losing heat, the refrigerant phase-changes into a liquid, moving on to the expansion point.
Expansion: Just before the evaporator is a tiny passage — a self-adjusting expansion valve or a fixed-orifice tube. A low-pressure expanse awaits in the evaporator.
Evaporator: Hidden inside the air box, the evaporator looks like a small radiator with fat tubes. Inside, the refrigerant phase-changes to a gas. It absorbs heat from the cabin air blown by the fan. The refrigerant then moves back to the compressor to start the circuit again.
Auto Air Conditioning System Troubleshooting
If you think your air conditioning might be broken, here are a few things you can check.
Cabin Air Filter: If air flow seems low but the air is cool, ask yourself when you changed the cabin air filter last. In some locales, dust and pollen can choke the cabin filter in just months, restricting air flow and impacting air conditioner performance.
Drive Belt: If a loose or contaminated drive belt slips, it may not drive the compressor. On some vehicles, belt slippage will disable the compressor altogether, usually alerting you with a warning light or message.
Fuse/Relay: Many belt-driven compressors use a cycling clutch controlled by pressure switches. Power to the clutch is fed by a relay, which is protected by a fuse. If your air conditioning isn’t working and the clutch isn’t cycling, check the fuses and try swapping in a different relay.
Refrigerant Pressure: Low system pressure can reduce air conditioning performance or disable it completely. With the vehicle off, the air conditioning system should have about as much pressure as the temperature, as in 71 psi on a 70-degree day. Some consumer refrigerant top-off kits have a low-side gauge for this purpose. If the pressure is low by more than 5 psi, suspect a leak and look for obvious damage or oil seepage.
The modern auto air conditioning system has been around since the mid-1950s, and current systems are easier to understand and maintain than ever before. Still, if you don’t want to do all of the maintenance yourself, your local trusted mechanic has the training and equipment for the job.
Check out all the air conditioning system parts
Photo courtesy of Flickr.
Ben has been taking things apart since he was 5, and putting them back together again since he was 8. After dabbling in DIY repairs at home and on the farm, he found his calling in the CGCC Automobile Repair program. After he held his ASE CMAT for 10 years, Ben decided he needed a change. Now, he writes on automotive topics across the web and around the world, including new automotive technology, transportation legislation, emissions, fuel economy and auto repair.