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Air Conditioning Repair

by Aaron Turpen

There are two maxims of air conditioning repair that every auto mechanic is familiar with:

  • If something is going to go wrong with the A/C, it will happen on the hottest day of the year.
  • If the A/C fails, it will likely be within the first 5 years of the vehicle's life.

Air conditioning repair can be relatively simple and low-cost or it can be extremely expensive. It all depends on what's wrong, what type of vehicle it is, and how difficult it will be to fix. If you understand how your A/C works and what some of the warning signs of failure might be, though, you can often take what could become a costly air conditioning repair and nip it in the bud.

How the Air Conditioning System Works

Refrigerant is compressed

Without getting into nitty-gritty detail on individual components, the gist of the A/C is pretty simple. It works on the principle of compression and induction. Your air conditioning starts at the pump. This is usually run from an accessory belt (serpentine belt) on the engine. The compressor does its job by compressing and pressurizing the refrigerant. This is pushed through the A/C line to the condenser where heat is blown off (the condenser is like a little radiator).

Typical automotive A/C system

Refrigerant is expanded and mixed with air

From there it goes into the drier and then the expansion valve. The EV controls how much gas is released into the evaporator, which causes the gas to expand. This expansion (since the heat is already gone) means the refrigerant suddenly goes cold. The cold refrigerant is sent through the evaporator where air is blown over it and cooled before entering the cabin where you feel the cold air coming from the vents. The refrigerant is then sent through the EV again to regulate its movement back to the compressor where the cycle begins again. Many EVs are now computer-controlled and very complex compared to the simple pressure-sensitive valves used up until just a few years ago.

Now that you know how the system works, let's look at the most common failures it will have.

Common A/C Failures and Air Conditioning Repairs

Leaking Refrigerant

The most common failure in air conditioning repair is leaking refrigerant. When enough leaks out, the system can't compress enough to make the evaporator cold enough to send cold air into the passenger compartment. Since the loop through which the refrigerant is sent is relatively large (encompassing the whole front end of the vehicle in most cases), leaks are hard to spot and rarely noticed until they become a problem for the delivery of cold air. To find a leak, use soapy water in a spray bottle to spray every fitting along the A/C lines and look for bubbles indicating a leak. Note the leaking spot, but continue through the entire line as it's likely there's more than one.

Note that there are specific state and federal laws about working with the refrigerants commonly used in vehicles, so DIY air conditioning repair may not be legally possible where you live.

Compressor Failure

Another common failure is in the compressor, which may stop working. As the only other moving part of the system (outside of the refrigerant), the compressor may have several things go wrong with it. Bearings may go out, causing the pulley to slip, the gaskets inside the compressor might fail or leak, compromising the system, etc. The air conditioning repair may be as simple as replacing the pulley or as costly as replacing the entire compressor.

Electronics failure

Finally, the electronics in the expansion valve may stop working correctly. In this case, a diagnostic computer may be required and component replacement needed.

Qualified person must handle refrigerant

In nearly all repairs, the refrigerant must be carefully evacuated by a person qualified to do so and then replaced once repairs have been completed.

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