Whenever I'm driving and then I stop, I can hear my a/c compressor running. When I confirm this, I turn on the fan and the a/c automatically comes on. Why is it doing that? When I turn it off, I turn off the a/c first and then switch the fan off. Is that correct? I hope someone can shed some light on this. Thanks in advance

 

When I stop, I can't hear my AC compressor running. The AC compressor is virtually noiseless. The only way I can tell from inside the car when the AC compressor comes on is to observe a barely noticable slight drop in the RPMs, instantly followed by an increase almost back to where it was before the drop.

When I stop, if the engine is warm, and especially if the stop lasts more than a few seconds or the outside temp is hot, I hear the big cooling fan between the radiator and the front of the engine come on and run. It makes quite a loud noise, easily detectable inside the car. This fan is not related to the AC system.

Nissan (like other manufacturers) intends that the AC be on most of the time. Cooling the inside of the car is only one of the functions performed by the AC. Probably its most important chore is to dehumidify the interior of the car.

You are in Vegas, where humidity is rarely a problem. In most parts of the country, humidity inside the car during cool weather results in the inside of the windows fogging over, making driving both difficult and dangerous. That is why the AC is as important in cold weather as it is in hot weather, and why the AC should normally stay on in all but very arid areas.

 

Thank you for shedding some light. You are right, it's the cooling fan that I hear, not the compressor. And you also answered my question abt the ac

 

Can the AC develop smells if we turn the compressor off while blowing plain air? I've heard that you should turn off the AC for a minute or so while still letting the air blow to "clear" the system, but I never knew why this was important. I've noticed that when I do this, it starts to develop a smell, but once I turn the AC back on, is smells fresh and new again.

So I've all but given up 100% on this procedure...and lately, I keep it on recirculate and AC going until the car turns off. I assume Nissan intends for me to do it like this.

 

This is sort of what I call the 'refrigerator syndrome'. If a kitchen refrigerator has been on and in use for an extended period, then turned off and emptied, and we come back in a few days and open the door, it smells awful. Simply leaving the door open for days does not completely eliminate the odor.

I think the proceedure you mentioned may be sort of a carryover from the days when AC systems were an option only used when needed to cool the car during hot weather and defog the car during humid, cool weather, because the compressors of those days measurably impacted the MPG.

Also, back in those days, we were advised to make sure to run the AC for several minutes every few weeks during the cool half of the year in order to keep all the seals lubricated and the system in working order.

You are correct that most manufacturers now intend the HVAC system on most cars be on virtually all the time. Where I live south of Atlanta, there may be less than a dozen days a year when I have the system totally off.

I remember the cars of the 1940s through around the 1980s, when there were vents and scoops and other means of bringing plain outside air into car cabins. I was not happy to see all those disappear, but gradually adapted to ever-changing times.

The days of bringing plain, untreated outside air into the passenger cabins of cars is almost gone. That can be a real problem if, for whatever reason, our AC system fails in hot weather. At that point, we have no option but to drive with the windows down.

The microfilter we have in the Maxima helps us to have cleaner air in the car than we would have if bringing in untreated outside air.