Q The air conditioning has stopped working on my 1997 Grand Caravan. The van stalled and would not start for about 10 minutes. After that, the A/C would not work. Is there an easy way to tell whether the A/C clutch failed, or the compressor? I think the car stalled because the A/C seized up.

A Open the hood and look at the air conditioning compressor. Make sure the serpentine belt is intact, properly tensioned and not damaged. With the car's ventilation controls set to "off," start the engine and look at the clutch/pulley assembly on the front of the compressor. The clutch should not be engaged -- the outer pulley driven by the belt should be turning, but the inner hub should not. If both are turning, the clutch is seized.

Now, turn on the air conditioning and look again. Both the outer pulley and the inner hub should be turning, indicating the clutch is engaged and driving the compressor. If the compressor is seized, the entire clutch assembly will be stationary and the belt will be slipping, squealing, smoking and, in a very short period of time, failing. Because of the need to recharge the system to replace the compressor, leave service to the pros.

Q I recently bought a 2010 2.0-liter VW Passat. Their scheduled free maintenance for three years or 36,000 miles calls for oil changes at 10,000-mile intervals with synthetic oil. Am I asking for major expenses down the road by following their maintenance program?

A I doubt it, but why not change the oil every 5,000 miles on your own nickel? It's cheap insurance.

Q I've got a 2000 Buick LeSabre with 59,000 miles that I purchased new. During the past six months, the check-engine light comes on and the dashboard message center tells me the gas cap is loose. This has happened more than 10 times. I've had the check-engine light cleared several times and I am certain the gas cap is on tight. Despite installing a new gas cap, the check-engine light still comes on.

The garage assures me all the emissions components are working properly and blames the problem on the car being rear-ended a year ago and suffering major damage. What can I do to correct this?

A The garage could well be correct. Residual damage to any of the evaporative emission components could be the problem. Have the shop identify the specific DTC fault code that is triggering the light. The self-diagnostic capabilities of the evap system can pinpoint vacuum leaks or problems with the fuel tank pressure sensor, vent valve solenoid, purge valve solenoid or charcoal canister.

Q I've got a 2003 Nissan Murano with 97,000 miles. When I drive slowly, like browsing garage sales, it gets balky and hesitant. The dealer found no codes in the computer, and they changed two air hoses and clamps. No help.

A Did the dealer also install an updated air intake duct, according to Nissan recall R0902 in July 2009? Deterioration of this duct can cause an erratic idle.

Motoring note "Back to the '50s" is just around the corner, but this Saturday from 11 a.m. to 4 p.m. you can get a sneak preview at the fifth annual Samaritan Tire car show in Minnetonka. The show is free, and proceeds from refreshments will benefit the Courage Center.