It's the first really warm day of the year and rolling down the windows just won't cut it to keep you comfortable. So you switch on the air conditioning and . . . no cool air. That scenario is how many people discover a problem with their AC, says Ben Lavine, service manager at Grossman Chevrolet-Cadillac in Burnsville. That's also when they discover that dealerships are backed up fixing other malfunctioning AC systems, resulting in waits as long as a week or more.

With older cars, you can test your AC on a mild day. But since AC systems in many newer cars won't work when the outside temperature is too low, technicians and service directors advise booking an AC checkup now. Dealers can check systems at full pressure, making sure there are no leaks and that compressors run quietly. And technicians like Brandon Holland of Walser Toyota Scion in Bloomington will also make sure your cabin filter and evaporator aren't clogged, which can lead to a moldy interior odor.

AC is only one item on a good get-ready-for-hot-weather checkup list. Experts advise having your coolant inspected and topped off to avoid a breakdown and possible engine damage. They also recommend making sure your transmission, brakes and differentials are ready for any towing you plan to do. And Greg Schiffler, manager of the Quick Lane of Inver Grove, located at Inver Grove Ford, recommends that a qualified technician check your front end to make sure ball joints and tie rods aren't loose.

Trained eyes should also inspect shocks, struts, hoses and belts. A checkup should also include a look at washer systems, air filters and tires, including spares, because tires lose about one p.s.i. per month.

As for oil changes, with motorists comfortable following manufacturer guidelines on fluid changes, doing anything before a particular mileage number is reached is usually not necessary for newer cars. Lavine recommends a tune-up for older cars, however, and Schiffler says vehicles coming out of storage should get an oil change because moisture gets in lubricants over the winter. Because wiper blades get "beat up in winter," he also advises replacing them, if necessary.

Here are some other reasons to consider letting a new-car dealership prep your vehicles for summer:

 

Dealers offer specials and are competitive with independents.

Dealers can do same-day checkups and many offer no-appointment drive-up services. Lounges are often equipped with Internet access, big-screen TV and more.

If a dealer sells the brand you drive, the technicians know it well. Dealer techs also have access to that brand's latest equipment, technical information and training.

The maintenance experts at autobytel.com recommend oil changes at dealerships because they're more motivated to use the proper oil for your vehicle. An article at that website says that oil-change chains are less likely to do that because they order bulk oil to keep costs down.

 

Unless there's a problem, your spring checkup can delay one thing: tire rotation and wheel alignment. That can wait until the worst of our annual "pothole season" is behind us.