# 99 altima ac



## tmoneymike (Jun 20, 2012)

There seems to be a little problem with the ac in the altima. The pump kicks on and the fan kicks on for about 30 seconds while driving,blows cold air, but right after it kicks off blows hot air heating the car up in about 10 seconds. Ive checked the pressure and it shows that it is in perfect pressure range. need help quick due to having to take my baby with me in about 110 degree heat.


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## smj999smj (Jan 1, 2006)

Have you check both high and low side pressures...or just the low side?


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## rogoman (Dec 16, 2004)

With the compressor cycling on/off every 30 sec or less might be due to a low refrigerant level. Just like SMJ said, you need a manifold gauge set that measures both the high and low sides.


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## tmoneymike (Jun 20, 2012)

i measured both sides both at normal pressure. it may be irrelevent but i left the car doors open with the ac running and it stayed on for a good 10 mins plus. started reving motor in a few second intervals and watched the pressure on the ac line drop past teh recharge line and the ac would kick off. let it idle again and kicks back on and stays on. So next questions is could it be a switch possibly and if it is whats the best way to test it.


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## smj999smj (Jan 1, 2006)

Try and locate a FSM for your Altima; in the heating and air conditioning section there is an "AC performance test" that will give you specific conditions and engine RPM to test the system and a range of high and low pressure readings that factor in ambient temperature and relative humidity. There will also be a section that shows what can be wrong based on what your gauges are reading. It's the best and really only the correct way to test your system properly. I've yet to see a professional gauge set that has a "recharge line," so I don't know what pressure that is supposed to represent. If the low side gauge is too low or going into negative pressure, it could be low freon or a couple of other things. Given that we don't know the conditions the system was tested under and what the readings actually are, it's difficult to guess what pressure is considered "normal" as there is such a variable of high side pressure ranges based on a variety of conditions. A "normal" high side pressure can run from 175 psi to over 300 psi depending on the conditions.


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