Why doesn't my car's AC work?

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 West)

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 West)

Trying to keep cool during the heat of summer is no joke, especially if you notice your car's air conditioning can no longer keep you comfortable.

So what do you do when you car’s air conditioning starts failing you? Turn to your trusted mechanic. Even if your A/C system loses performance gradually, it can indicate a larger problem.

Recharging your car's AC system

One of the most common reasons for failing or diminished cooling in your car is insufficient refrigerant due to a leak in the system. Your car’s A/C, much like your home’s A/C or refrigerator, depends on the thermodynamic properties associated with coolant gases operating within a closed loop under the correct pressure.

If the car’s A/C system has a coolant leak, you may notice your car can’t keep the interior as cool. “If your A/C system is low on refrigerant, it’s obviously leaking,” says Andy Milot, owner of highly rated Andre’s Auto & Truck Services in Oldsmar, Fla.

So you should be able just top off the system with some fresh coolant and get your interior back to chilly comfort again, right? Not quite. For starters, if your car is leaking coolant, you’re harming the environment, particularly the ozone layer. Older cars use a refrigerant compound known as R12, or the more common brand name of Freon, which falls into the class of chemical compounds known as chlorofluorocarbons or CFCs.

"A/C systems are pretty much maintenance-free – so they never need a charge until they leak enough refrigerant out," says Bill Coniam, owner of highly rated 25th Street Automotive in Phoenix. "If you have a leak, it is your environmental responsibility to try to find and correct it."

If your system does leak, Jones recommends asking your auto shop to perform a pressure diagnostic and leak evaluation, which he says can cost from $80 to $150 in most cases. The technician will top it off with coolant and pressurize it, then look for leaks. Sometimes, an ultraviolet dye may be added to help find the technician find small leaks.

Coniam says you should expect to pay a little more than $100 for an A/C recharge and leak diagnostic, but to be wary of extremely low prices for the service. "Advertising something a $19.95 A/C service is misleading. At that price it makes me suspect that they aren’t environmentally friendly and/or they intend to try to sell unnecessary services," he says.

Can you recharge your car's AC yourself?

Do-it-yourself recharge kits are available, but may pose some environmental risks. "You have to be very careful," Lucido says. "That’s an advantage to taking your car to a shop: We’re licensed to do this. Otherwise you could be releasing CFCs into the atmosphere."

Lucido adds that although the retail A/C recharge kits come equipped with generic gauges to measure the amount of coolant in the system, they're not as accurate as the gauges a professional mechanic would use. "You really should have pressure gauges if you’re putting Freon into a system - there’s a happy medium you have to achieve," he says. "If you put too much Freon in, it won’t cool; if it's low, of course, it won’t cool well."

Costs for car AC repair

Consider yourself lucky if your A/C problem originates from a lack of refrigerant due to a minor leak. “Air conditioning can be terribly expensive to repair,” Milot says, adding that there’s a wide range of repair possibilities and costs. “A leak or a problem with your A/C system could cost as little as $2 for replacing an O-ring to at least $1,000 for something like a compressor failure.”

Symptoms of failing air conditioning components can include loud screeching that's continuous or upon starting the vehicle, coupled with loss of cooling output. "That can mean you have an A/C compressor about to lock up," Jones says. 

Coniam says other symptoms such as rattling or poor air flow from the vents can help indicate the difference between a major repair like an A/C compressor, or a minor one like a bad blower fan. "Many times the problem lies in the air distribution system under the dash, not the refrigeration system under the hood," he says. "So look for things like air that doesn’t flow or has insufficient flow or doesn’t flow from the correct vents."

Jones says replacing A/C components such as compressors, condensers or evaporators can start at about $800 and can easily cost $2,000 and more.

While the parts themselves are costly, the labor required can dictate higher prices on some A/C repairs.

If you’re shelling out big bucks to invest in new air conditioning components in an older vehicle, don't forget to ask the repair-or-replace question. “You always have to look at the value of the car when you’re doing a costly repair in my opinion,” Lucido says.

Editor's note: This is an updated version of an article originally posted on July 16, 2012.


I have a 2001 dodge dakota the ac clutch works for 10 seconds stops for 3 so on. system is full. no cold air at all.What could be wrong?Thanks.

I have a Ford Focus station wagon year 2000. My car only has 34,500 miles on it. For several summers my air conditioner did not give out cool air. Whe I turn it on there is no problem with the blower but it just blows warm air. I have taken it to have the air conditioner checked, they put dye in it and confirmed that there are no leaks. They then add refrigerant and the car is cool for the summer but this has to be repeated every summer. During the winter months there is no problem with heating the car. I have no other car problems.

As mentioned back in the article, CFCs, which do actually cause significant damage to the Ozone Layer was all over the place - in hair spray, fog horns, keyboard cleaners, everywhere. It was just jetted out and made an excellent, non-toxic, propellent. The chemicals were used massively, around the world. That is not the case anymore. CFCs have been eliminated from cars since the early 1990s and replaced with HCFCs (i.e. R-134A) which have an ozone depletion capability of only 5.5% of CFCs. Plus, the real culprits, intentional direct emissions, are gone. The bottom line is that if your leak is relatively slow, keeping it refilled will not destroy the planet, in any way at all, but will save you boatloads of money that you can use to feed your family. That is why refill kits, with HCFCs, are still available to the public.

My overly-loved 2005 Honda CR-V (225,000 miles) has an AC that works intermittently. What's causing that? Could it be a thermostat malfunction not telling the compressor when to cycle on/off properly?

My 1997 Volvo 850T blows black smoke out of the rear of the car when the AC is on. What does that mean? I took it to the volvo dealership and they cleaned it and replace some valves???......but it still does blows black smoke. HELP! I love this car......except for this AC problem, it's been great and I feel I can still get lots more mileage from it.

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