I have a nissan altima 2000. Having problems with a/c unit. The a/c seems to work least during the hot humid summer months. At times, I can hear it click on and it works fine. Most of the time it does not. The a/c was checked out for leaks. None were found. Have taken car to 3 car shops to fix. They find nothing wrong with ac unit. Any advice?
Sounds like an electrical problem. This car has two pressure sensors that will cut off the compressor to prevent damage. The lo-pressure sensor will cut the compressor if the sensor reads lo-side pressure too low, as if it has a leak. The hi-pressure sensor will cut the compressor if the hi-side pressure goes too high, as if there is a blockage in the system. But, if either sensor is broken or damaged, that could keep the compressor from turning on. A simple check with a multimeter will confirm if this is the case.
Does this one have one of those fancy systems that controls the A/C temperature for you?
Thank you for the advice. I’m having it check as you said.
When it works, does it keep on working until you turn it off? If so, you may want to check the A/C switch in the thermostat and the compressor relay. With age and use, the contacts degrade and cause intermittent problems.
yes, once it is working it will work until the car is turned off. When it works, it’s great but when it doesn’t it’s miserable.
Check to make sure you have full voltage at the compressor relay coil. Then check to make sure you have full voltage at the compressor. The relay might not pull in with too little voltage (and wear out faster due to slower switching) and the compressor would have a harder time starting up at reduced voltage.
Since it seems to work perfectly when it does, it’s not likely a refrigerant system problem.
When it doesn’t work, does the condenser fan spin? Can you get it to work sometimes by tapping the compressor relay with a screwdriver handle with the power on?
I always like knowing what the high/low side pressures are, but since that is not known I’m going to make a guess at a faulty thermistor (probably) or a low pressure switch (possible) cutting out.
Thermistors have been a problem at times on Nissans.