Hi adoyle2009. Welcome to the forum. Doesn't sound like a compressor problem. When they fail, they don't magically start working again. The dealer is right that there isn't much they can do when the problem isn't occurring. When the system works, you have to agree every part is working so there is no defect to be found. That is hard for some people to understand. I often ran into the same thing on house calls when fixing peoples' tvs. The exception is when your description of the symptom is a very common one with a known pattern failure. In this case, it sounds exactly like a problem a few Chrysler minivans had in the late 1990s. The cause was an intermittently sticking "H valve". If it stuck closed, no refrigerant entered the car to do its cooling. If it stuck open, too much refrigerant entered and the evaporator in the dash got too cold. The humidity that condenses on the evaporator and is supposed to drip out the bottom of the car freezes instead into a block of ice that blocks air flow. Either problem was intermittent but it was so common, the mechanic didn't even bother to do any testing; he just replaced the valve.
Other manufacturers have their own name for an H valve but the symptoms can be the same. An intermittent electrical issue can also cause your symptoms. The thing to do is to peek under the hood when the no-cooling problem acts up and see if the AC compressor is running. If it is not, that will provide important clues for the mechanic. On most systems the compressor cycles on and off roughly every 5 - 30 seconds so you can see what it looks like. No other belt-driven pulley turns on and off. If yours runs continuously, have a helper turn the AC on and off until you can see which pulley is engaging. You can also have a mechanic point out which pulley is for the compressor so you will know which one to check.
Friday, June 25th, 2010 AT 2:41 PM