Air Conditioning... isn't

My truck's about 7 years old, but AC's seen less than 4 years of actual use (three years in England I think we used the AC once).
Recently, it's begun blowing not-so-cold air. In fact, the air temp out
of the vents seems about the same whether the AC is on or not. I'm guessing it needs to be recharged, but a coworker said that my AC isn't old enough to need that...
Should I be looking at other reasons as well? Everything seems fine, I can hear the compressor come on, truck isn't running hot or anything.
I've got an appt next week, since it's already in the 100s here much of the time (though today, thankfully, it only got up to about 79f).
jmc
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The A/C system may be low on refrigerant. Does the compressor come on and stay on for a fairly long time, or does it come on and then shut off fairly rapidly? If it cycles quickly (short cycling) that is usually an indication that it is low on refrigerant. If the shop finds that it is low on refrigerant, have 'em do a leak test. If no leak is found, have them add a fluorescent tracer dye to the refrigerant when they recharge the system. This will make it easier to find the leak if one is present.
Good Luck!
Mike
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Suddenly, without warning, Mike Simmons exclaimed (12/10/2007 7:48 PM):

Thanks. I hadn't noticed how quick it's cycling. What's a normal compressor cycle?
jmc
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Depends on the ambient temp but probably at least 30-45 seconds run time... many times longer... a short cycle is more like 3 seconds on 10 seconds off... 3 seconds on... ten seconds off... you get the idea.
Mike

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the worst thing you can do for an ac system is not running it at least once a month. the seal around the shaft in the compressor must have oil circulated every once in a while to keep it doing its job. my first guess would be a leak in this area. you need to hook up a set of manifold guages and see how much pressure you have on both the high side and low side. if it is low on refridgerent then top it off and run it a while. if you loose that batch then start looking for leaks. a decent leak detector kit is not that expensive. i personally don't believe in adding system sealer. it just adds problems down the road. michael
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