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UNDER THE HOOD

QUESTION: This may be the dumbest question, but why does water drip from beneath my car when I use the air conditioner? I know it's normal, but wondered where it comes from.ANWSER: The only dumb question is the one not asked.Besides reducing the interior temperature of your car, the A/C system also reduces humidity. Under the passenger-side instrument panel is a heat-exchanging device called an evaporator. As outside or recirculated air passes across the evaporator's labyrinth of cooled fins, moisture condenses on them and drips to a collection tray and drain below.On humid days, it's not unusual to see a large puddle of water appear beneath the vehicle after it has been parked. An undesirable aspect is that residual moisture and airborne debris can combine to cause microbial growth and odor. Switching back to "outside," rather than the "max" or "recirculation" position during each day's final moments of operation can help dry the evaporator case, reducing the chance of odor-causing growth.

QUESTION: My SRS (air bag) light just came on and they tell me I need a new clock spring, which is big bucks. What does this part do? Is it possible to change myself?ANSWER: Vehicles equipped with SRS (supplemental restraint system) utilize a part called a clock spring just behind the steering wheel that provides a reliable electrical connection between the driver's air bag, through the rotating steering wheel, to its control module within the instrument panel. In the past, a single sliding contact provided the horn connection, and on some vehicles additional sliding contacts were used to provide a path to in-wheel cruise control switches.Air bags require scrupulous reliability, so a spiral wound ribbon cable was developed to provide a plug-in, one-piece connection for the air bag, horn and other steering wheel-mounted controls. The clock spring can rotate a few turns in each direction, winding and unwinding, as the steering wheel is turned.As with any mechanical device, friction can take its toll, tugging on the ribbon cable's connections, causing a circuit failure. The SRS system's diagnostics identified the fault, and the illuminated SRS light warned you of suspended SRS functionality and the need for service.Can you renew the part yourself? I wouldn't recommend it, unless you have access to detailed SRS repair/replacement information, a steering wheel puller and have more than moderate hands-on experience repairing automobiles. The greatest concern when servicing an SRS-equipped vehicle is powering down the system before proceeding with any work. (This includes allowing the back-up power supply to drain.)An accidental air bag deployment can severely injure you should improper service methods be employed. The clock spring also must be carefully oriented (centered) so its limited travel is in harmony with steering wheel rotation.Brad Bergholdt teaches automotive technology at Evergreen Valley College in San Jose, Calif. E-mail him at under-the-hood@juno.com or write to him in care of Drive, Mercury News, 750 Ridder Park Drive, San Jose, Calif. 95190.

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