Hello all, I'm new here but info I gained here sold me on my Xterra. Just recieved my 05 OR 4x4 in Night Armour 1week ago and love it. Was a big change going from a Bimmer to an SUV but don't regret my choice at all. Now the big question has anyone else here noticed the AC compressor runs as soon as you turn on the fan. AC switch is off and temp knob is turned to heat. I thought ac compressor only ran with ac on, am I wrong?

I dont know about the 05's, but on my 04, when ever I have the defrost on, the compressor clicks on and off. As I recall It has something to do with the humidity I think. Does the compressor run when you have the knob set to floor?

One of you brave fellows is going to need to break into that dash at some point and figure out how to disable it. On the first gen Xterra it's a pretty simple task and it's nice to have full control.

On newer vehicles the defrost works with the AC on as this is the fastest way to get humidity out.

I understand that the AC helps clear the moisture, and thus the auto on when set to windshield. But, why, just why should it stay on when you move it to another setting unless you reset the system. Sounds like a design flaw to me. I am willing to bet that the 06's AC will turn off if you move it away from windshield.

I've seen some manufacturers setup the defrost so that the compressor comes on unless the temps are below a certain temperature. In my old Grand Am, the compressor would not come on if the temps were below 40 degrees. Much less humidity at lower temps.

I'd put money on that... Nissan has been using this same design for years, now. I don't think it's a design flaw, in their eyes. Not sure why they do it, but there's some reason for it, anyways. Somebody, somewhere in a meeting room, thought it was a good idea, and convinced the others.

Really, though, I wouldn't worry about it. Worse case scenario, is you lose .25 mpg or so, tops. I don't think you'll ever miss that.

Yea, its weird because the A/C light doesn't come on either, but its all by design to reduce humidity as fast as possible so you can see where your going, so you don't have to think about it maybe? What I don't quite like is that the vent air, when NO A/C is running and the temp is turned all the way cold, always seems to be *slightly* warm.

Nissan changed it so the compressor doesn't shut off even after you de-select a (full or partial) defog setting because the windows rapidly fog up heavily as the moisture that had condensed on the evaporator is released into the cabin as the evaporator warms up again.
Same as the change made for the 2003 models.
http://www.nissan-techinfo.com/nissan/TSB/Feb/54301.asp

The 2000-2004 models also had a problem with the air being warmed somewhat in a non-AC vent mode. The fix for the early models that were especially bad about it was to drill out the holes in the cowl, or get the cowl replaced with a less restrictive version:
http://www.nissan-techinfo.com/nissan/TSB/Feb/53899.asp

Mythbusters (the TV show) proved it's MUCH more than .25 mpg, it's more like 25% worse fuel mileage. Episode 22 (Nov. 10, 2004) of Mythbusters proved that running the A/C was HORRIBLE on gas mileage period using identical vehicles with identical amounts of gas. If all you lost was ¼ mpg every vendor would have it on. It's not on in my MINI or my Subaru unless I turn it on or it's on full defrost but when I leave full defrost it's off.

In fact, the manual says Nissan leaves it on at any temp above 36°F (37 in 04) until you turn the blower off (in 04 it stays on until you turn the X off). It's a crappy design IMHO and needs to be revisited. I've considered a simple cut off switch to the A/C fuse but haven't been quite gutsy enough to add it just yet.

The compressor shuts off when the blower is shut off on all vehicles, otherwise the evaporator would ice over.

I watched that show too, but the problem was they weren't running at hwy speeds. If they had increased to speed to 70 MPH, I think you would have seen drastically different results.

Mythbusters (the TV show) proved it's MUCH more than .25 mpg, it's more like 25% worse fuel mileage.

I track my mileage on all my cars by resetting the odometer each time I fuel up and calculating the mileage for each tank. When I run the air conditioning I rarely see a loss of mileage of more than .5 mpg (on vehicles that average at least 20 mpg). No way have I ever seen even a ten percent decrease in mileage.