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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.

The lifeblood of an air conditioning system is the refrigerant. Over the years there have been several different refrigerant types used in automobiles. Most people use the term "Freon" to describe all refrigerants, but in actuality it is a brand name mostly associated with R12 refrigerant. R12 refrigerant was used for decades until it was banned in 1996. The chemical makeup of R12 makes it very bad for the environment so it was phased out. Next came R134a which was found to be more environmentally friendly while still working similarly to R12. In fact some R12 air conditioning systems can be converted to R134a with the right steps. But R134a was eventually shown to also damage the environment, so something new had to be found. The current improved refrigerant is 1234yf and has already been put into use by almost every automaker. It is important to note that you cannot mix any of these refrigerants.

Each air conditioning system is also designed to hold a precise amount of refrigerant. Having too much or too little refrigerant leads to the system not performing at peak cooling ability.

Here's a basic summary of how each part of the air conditioning system produces the aforementioned phase changes from liquid to gas and keeps the vehicle's 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 items your mechanic will check.

Cabin Air Filter: If air flow seems low but the air is cool, find out when the cabin air filter was last changed. 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 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 the air conditioning isn't working and the clutch isn't cycling, the fuses should be checked and perhaps a different relay should be swapped.

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. If the pressure is low by more than 5 psi, the mechanic will 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. The expert mechanics at Don's ProTechnology Auto Repair have the training and equipment for the job.

Feel free to make an appointment for your A/C recharge or diagnostics at Don's Pro Technology Auto Repair. The shop is located at 230 E. Tehachapi Blvd., in Tehachapi and can be reached at (661) 822-1600.