Angie's LIST Guide to
Car air conditioning

No modern car comfort commands as much respect as air conditioning. If you’ve ever driven on a hot summer day without the benefit of AC in your car’s cabin, you know the value of a working air-conditioning system. Learn all about how AC works and common AC system problems below.
 

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(Photo by Fred Patton)
(Photo by Fred Patton)
 
 

How car AC works

A car’s AC works much in the same way a residential air conditioning system works, but on a much smaller scale. The first and most important element is refrigerant. In the case of most vehicles built after the 1990s, the refrigerant of choice is R134a. It’s less damaging to the environment, the ozone layer in particular, than its pre-1990s predecessor, R12 (also known by the brand-name Freon).

A car’s AC depends on the thermodynamic properties associated with these operating within a closed loop under the correct pressure.

Refrigeration cycle

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Unfamiliar with the inner workings of your car's AC system? Get professional help to keep you cool. (Photo courtesy of Angie's List member Brandon W.)

1. The thermodynamic properties of refrigerant gases under pressurization are a complex process, but in a nutshell, when refrigerant in its cool liquid form is exposed to warm air, it evaporates into a gas and absorbs or removes heat from the surrounding environment. This occurs in an AC component in the car known as the evaporator. It’s important to note here that an AC system doesn’t technically produce cool air, it removes heat from the air via the evaporator, then relies on the car’s blower and air ducts to blow cool air out into the cabin.

2. Now that the refrigerant has removed heat from the cabin, the hot refrigerant in gas form  then travels to a separate part of the system, where the gas is compressed by the compressor.

3. Already heated by absorbing heat through the evaporator, the compression process creates even more heat. To remove this heat and once again cycle cool liquid through the system, the hot refrigerant gas is forced through a series of coils in the condenser, which is similar to a radiator in that it dissipates heat. The pattern of the coils creates a wide surface area in a compact space. Blowing air across this surface (created by the vehicle’s movement or a fan), dissipates the heat, turning the refrigerant gas back into a cool liquid.

4. Before the refrigerant can cycle back through the system, any water that may have been created in the process needs to be removed. This is achieved by a component known as a receiver or dryer. Once the water is removed, the refrigerant can start the cycle all over again.

Recharging AC refrigerant

If you've noticed a lack of cooling output by your car's AC, but components like the blower motor appear to operating correctly, a likely cause is a refrigerant leak in the system. R22 or R134a refrigerant itself never degrades or distengrates if it's in a sealed, pressurized system, so if an AC system is low on refrigerant, there is almost certainly a leak in  hose, connection fitting or AC system component. Because refrigerant is highly damaging to the ozone layer, it's a car owner's environmental responsibility to diagnose and repair a refrigerant leak as soon as possible.

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A qualified auto technician can evaluate and repair vehicle air conditioning refrigerant leaks. (Photo by Fred Patton)

Leak diagnostics

For all but the most savvy DIY mechanics, the best way to evaluate and diagnose a refrigerant leak is to visit a trusted mechanic or auto service provider and request a leak diagnosis. In this test, which can cost $80 to $150 on average, a technician will top it off with refrigerant and pressurize it, then look for leaks originating from hoses, componets or fittings. Frequently, a UV dye may be added to the refrigerant to help find the technician find small leaks with the aid of UV lamp.

Once the leak has been located and repaired, the system can then be recharged to ensure it contains the correct amount of refrigerant. 

Avoid 'topping off' refrigerant

If you've ever visited an auto parts retailer or the auto parts section of a big-box store during the heat of the summer, you've probably noticed DIY refrigerant recharging kits for sale. These kits offer the at-home cost-savings over having a qualified mechanic recharge the system, but come with certain drawbacks.

First, if you're not repairing the leak that's caused a low refrigerant level in the system, the system will continue to leak. Not only is this bad for the environment, it will eventually necessitate recharging the system again. Second, the refrigerant in your car's AC system operates under pressurization and correct system pressurization means less wear and tear on system components. A qualified technicians or shops will utilize much more senstivie pressure gage when recharging the system and ensure it's recharged to manufacturer's specifications.

Expect to pay more for R22

Since R22 refrigerant was phased out of production and widespread use by Environmental Protection Agency regulations starting in the 1990s, drivers of older vehicles that use R22 should expect to pay more for refrigerant recharging services. Although R22 is still availble, supply is reduced every year, increasing its cost.

AC component repairs

If your AC problem originates from a lack of refrigerant due to a minor leak, it will cost significanlty less than component repairs. If your air conditioning trouble originates from anything other than a simple leak, there's a wide range of possible costs and repairs. Something as small as an O-ring for a hose may cost as little as $2, but replacing any major component such as condenser, compressor or evaporator can easily start at $1,000 and rise quickly.

While the parts themselves are costly, the labor required can dictate higher prices on some AC repairs. Disassembling complex interior pieces such as the dashboard may be necessary for some AC repairs, which can take even the most experienced many hours.

Symptoms of failing air conditioning components can include loud screeching that's continuous or upon starting the vehicle, coupled with loss of cooling output.  Other symptoms such as rattling or poor air flow from the vents can help indicate the difference between a major repair like an AC compressor, or a minor one like a bad blower fan. Problems attributed to the vehicle’s air conditioning itself can often turn out to be the air distribution system, which includes the vents and a blower motor for the fan.

Tips to keep your car cool

Turning on your air conditioning isn't the only way to keep your car cool during hot weather. Use these tips to help cut down on high temperatures and uncomfortable conditions in your car:

1. Use a sunshade or window visor. This tried-and-true method of keeping your car cool should be your go-to option to counteract hot interior temps throughout the summer. Put up a sunshade or window visor every time you exit your car for more than a few minutes. Keep it even cooler for long periods by putting a sunshade in your rear window as well.

2. Use a dash cover. A fabric or upholstered dash cover can go a long way towards making your car's interior more comfortable. You won't feel as overwhelmed by the heat if you don't have to touch hot vinyl surfaces. Dash covers also protect sensitive vinyl from sun damage that can cause cracking and fading.

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(Photo courtesy of Angie's List member Bill N.)

3. Cover your steering wheel with a hand towel. Even if you use a sunshade, it's a good idea to cover your steering wheel with a small towel. This will help to keep the contact temperature of your steering wheel down.

4. Park in a shady area. Whenever possible, park in a shady area. If you're going to be somewhere for an extended period of time, it's worth it to walk a bit farther in order to park in the shade. You'll be happy to enter a not-so-hot car when you return from your day out.

5. Keep your precious possessions out of the sun. Any tapes, CDs or delicate items that you keep in your car should be stored out of the path of direct sunlight. Try storing your tape and CD cases underneath the seat. You can also throw a blanket over your precious possessions. If you can't find a place in your car that will conceal heat-sensitive goods, consider placing them in the trunk.

6. Park in a garage when possible. Whenever possible, park in a garage. Your car will be out of direct sunlight and will have the benefit of near-constant shade. Even a warm garage beats being parked in the sun all day.

7. Keep windows slightly cracked. While it's not a good idea to leave your windows all the way open, it is a good idea to leave them slightly cracked. Check to be sure that you can't fit your arm through the crack in your window. Even a small crack will promote ventilation and help to keep your car cool.

8. Purchase a solar-powered fan. Paired with cracked windows, a solar-powered fan can make your car feel downright pleasant during even the hottest summer days. These simple fans work  to expel hot air from your car. By creating constant air circulation, they lower your car's overall temperature.

9. Throw blankets over your seats. If your car features vinyl or leather seats, you know just how hot these materials can become when exposed to sunlight and high temperatures. To keep car seats cool, throw blankets over them. When you return to the car, you can place the blankets on the floorboards or toss them in the trunk. Keeping your seats cool will make your car more pleasant on hot summer days.

Comments

I know you know the difference but you said R22 instead of R12?

Expect to pay more for R22

Since R22 refrigerant was phased out of production and widespread use by Environmental Protection Agency regulations starting in the 1990s, drivers of older vehicles that use R22 should expect to pay more for refrigerant recharging services. Although R22 is still availble, supply is reduced every year, increasing its cost.

I always wonder why don't car mfgrs. build stand-alone units that fit in the cabin or trunk, so repair and replacement would be a lot easier, and it would decrease maintenance costs for the engine and transmission by not being in the way.

I've seen some vans and pickups in TX with home AC window units permanently installed and run off inverters. That looks bulky, but a streamlined version would be a big hit here!

Clarifications:

R-12: Used in vehicles built before 1993
R-134: Replaced R-12 in vehicles built after1993
R-22: Used in home air conditioning systems, not compatible with car systems, also now banned like R-12 was in cars. (R-424a, R-428a, and R434a are a few of the HCF replacements currently being used along with others).

Yes, a failing o-ring seal might only cost $2 for the part but the labor involved in doing the replacment might take hours , which is where the real expense is.

And don't forget to bring the car in for repairs at 4:30 on a Friday afternoon after driving it for a good distance so everything is nice and cool to my asbestos like skin, and don't forget to sit and wait in the 74 degree waiting area whilst I roast alive working on your flaming hot car.
And then complain why it cost so much without any idea of the fact that to get to your tiny 2 dollar o'ring I needed 2000 dollars worth of tools and a stick of dynamite to move the other 8 things they crammed in the way of this o'ring.

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