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BACKYARD MECHANIC: No need to get stranded by faulty AC


2017 Honda Civic 4dr CVT LX for $0

2017 Honda Civic 4dr CVT LX

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QUESTION: I own a 2001 Honda Civic automatic sedan, and so does my friend. This past summer, his A/C stopped working and, shortly after, his car died and he had to have it towed and had about $1,000 work done to the A/C system (condenser and pump replaced, he said). He also incurred a hotel bill and meals for a couple of days over the weekend until it could be fixed.

I'm not sure why, but he claims that the car would not run because of the A/C unit malfunction. I've never heard of that before, and not sure why that would be. Now I'm concerned about my own car, as I don't want to get stranded on the side of the road and incur towing and accommodation expenses. If my A/C did stop working, I wasn't planning on fixing it, given that it is 11 years' old with over 300k and A/C is really not a necessity here. But perhaps that is not possible, if it affects the operation of the engine?

ANSWER: The air conditioning compressor (pump) is the only part of the A/C system that could conceivably stop the engine so the vehicle would need to be towed. But even this would be a rare situation.

The compressor uses a belt drive to rotate it on almost all vehicles. Some of the hybrid and electric vehicles use an electric motor-driven compressor. The belt turns a pulley on the front of the compressor and this pulley spins on a bearing that is pressed onto the stationary compressor body. This pulley is turning all the time the engine is running, so if the bearing were to fail, the pulley could potentially lock up and damage the belt, requiring the car to be towed.

When the A/C is turned on, an electromagnet on the front of the compressor pulls a clutch plate into engagement with the rotating pulley. This clutch plate drives the pump inside the compressor body. With the AC on, much of the load on the pulley bearing is reduced, but it's still supporting the pulley and rotating all the time.

Usually, if there is a problem developing with this pulley bearing, it will produce a growling, low-pitched rumble sound or vibration long before it fails, giving the driver the opportunity to have it repaired without being towed.

As for operating your car without the A/C working, that won't affect anything other than your comfort. You could change the pulley routing and belt on the engine to a model that doesn't have A/C. This would eliminate the compressor completely.

However, the simplest solution would be to leave everything in place and just make sure the compressor pulley bearing is in good shape. A skilled technician listening to the bearing with a stethoscope can usually detect any bearing problem long before it causes other problems, and replace the bearing.

QUESTION: I have a 2005 Mazda 3 my wife uses to get back and forth to work and she is only 2 minutes away from work. The car is not used otherwise. I find that the battery in colder weather needs to be put on a charger once a week. I have had the battery checked and the charging system and its OK. Is there anything I could do to make the car charge better on short trips like she does? Thanks.

ANSWER: In cold weather (-30C or colder) it can take up to half an hour for the charging system to warm up the battery before the battery will accept a charge. That's why frequent short trips in cold weather will cause the battery to discharge.

The solution? Warm the battery up before you start the car. This can be done by installing an electric battery blanket and plugging the car in so the battery is warm when you start the engine. You could also install a 2 amp or less trickle charger or battery tender to keep the battery warm.

Short-trip driving still tends to discharge a battery because the heater, headlights, rear defogger and other accessories use much of the alternator output and the starter drains the battery to some degree every time it's used. An occasional longer trip or using a battery charger would be your best solution.

Jim Kerr is an experienced mechanic, instructor of automotive technology, freelance journalist and member of the Automobile Journalists' Association of Canada.