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Q I have a 2005 Dodge Grand Caravan that has lost its air-conditioning cooling capacity. It did this about 15 months ago, and I had it recharged by the dealership. No leaks were detected. Because we're heading into winter, should I just wait until next summer to recharge and check it again? Is leaving the system discharged for so long bad for the air conditioning?A First of all, the fact that the system stopped cooling and needed recharging confirms a leak. Because automotive A/C systems cannot be permanently sealed because of installation and repair requirements, some loss of refrigerant is normal. Over the five-year life of your vehicle, that loss may add up to the point where the system doesn't work. This does not necessarily mean the system is completely empty of refrigerant. Typically, after about one-third of the refrigerant -- R134A -- is lost, the pressure switch will not allow the compressor to engage.

If the system isn't completely empty at zero pressure, no moisture or debris can enter. But of course the system will not defrost the windshield, demoisturize the interior or circulate refrigerant oil to keep the seals lubricated this winter. And it won't cool you down next summer. So you're faced with the "pay me now or pay me later" question. I'd be inclined to find and fix the leak now, have the system recharged, benefit from the defrost capability this winter and enjoy a cool interior next summer.

Q My wife loves her 2003 Toyota 4Runner with 50,000 miles on it. I don't drive it much, but last time I did, it drove as if the front tires had less than 20 pounds per square inch (psi). They have 35 psi. The dealer said it feels fine, and the alignment guy said it feels a little heavy but otherwise fine. I had the power steering flushed and refilled, but it still feels stiff. Now you have to heave it into a turn, and it remains turned until you steer it back. Any ideas before I start replacing expensive parts?

A Here are the typical causes for heavy steering effort; tires, suspension components, steering gear or steering column. The quick test for mechanical problems is to place the front end on jack stands supporting the suspension at normal ride height. Start the engine and turn the steering wheel in each direction. If there's any heaviness or binding in the steering, look for worn or damaged tie rods, ball joints or McPherson strut upper bearings. The lack of self-centering when you release the steering wheel in a turn points more toward a mechanical issue with one or more of these components.

To isolate the possibility of a problem with the steering rack-and-pinion gear or steering column, disconnect the outer steering tie rods from each side and retest. If the heaviness or binding is still there, disconnect the steering column from the rack to see if the binding is in the steering column itself.

Q I have a 2004 Jeep Grand Cherokee with tire pressure sensors. Upon start-up, the overhead console displays "TIRE SENSOR -- BAD/MISSING," but the display shows all tires at the appropriate pressure. Each time, we have to reset the console to clear the message so the clock and temperature display again.

Two dealers have checked but offer no solution other than to replace the sensors in the wheels, which is very costly. A tire dealer upon rotating the tires confirmed they were all transmitting the correct frequency, and in fact the display shows the exact pressure in each tire. Do you have any thoughts on the matter?

A According to my Alldata automotive database, the tire pressure monitoring system in your vehicle displays pressure in all four road tires plus the spare tire if the vehicle is equipped with its original steel-wheel, full-size spare. Could this be the missing sensor?