You have a bad solder connection at the rear blower motor relay that is mounted on the circuit board of the A/C controller.
This relay is the last thing in line from the fuse through the rear blower motor, through the switches through the relay to ground. The job of this relay is to turn off the rear blower if you punch the front A/C master control to "OFF" (which I can never recall doing).
Replacing the A/C controller will work, but it is expensive. Paul Miller reports that the cost at his Nissan dealer was $400 to "repair" it (no guarantee) or $750 to replace the part (90-day guarantee). We found out about 9 months after the fact that Paul had independently discovered this whole issue about when I did!
I just bypassed the relay. I used a short piece of 8 gauge wire (to be sure I could handle the current) with male crimp-on lugs on each end and plugged them into the connector that normally plugs into the back of the A/C controller. The relay has its own two conductor plug separate from the other stuff plugging into the A/C controller.
The bypass is really easy to do. When you got to the circuit board to remove it, there were wiring connectors that you had to unplug in order to take it out. One on the connectors just had two big wires... To bypass the relay, all you need to do is to connect one side of that two wire connector to the other side. It will then stay disconnected from the circuit board, hanging loose behind the A/C controller. You won't plug it back in.
To make a bypass wire that plugs into the connector from one side to the other, all you need is a small piece of 8 gauge stranded wire (about 2 inches...) and a couple of crimp on male lugs. Here's a link that shows a picture of these lugs.
The "male" ones plug into the "female" ones. You'll put "males" on both ends of the little bypass wire, and plug one into each side of the 2 wire connector, to electrically connect both of the wires together. You local auto parts guy should be able to help you find the wire and these lugs, and he'll probably put them all together to make the bypass connector for you.
Here is the wiring diagram for the rear A/C. And here is the wiring diagram image of the relay in the controller.
Here are the instructions for removing the A/C controller from the dash. It is not hard to do. Here's a couple of pictures to show you what the job looks like.
Also, David Massey sent me a wonderful set of step by step pictures. I am just posting to links to the jpgs here to save a bit of bandwidth, but be sure to check them out
Here's the wiring from behind the unit. See the 8 gauge red and black wires with the white connector (circled in the bottom left)? These are the wires to the relay
Once you get the unit out it will look like this:
You can now see the connector. I just connected one side to the other on the "car" side of this connector to bypass the relay. The effect of bypassing the relay is that if I punch the master OFF button for the A/C, I'll have to turn the rear blower off separately using either the rear blower motor switch or the front slide switch override. Big Whoop <tm>.
After I did this bypass, someone else I conversed with about this was going to do the bypass trick, but pulled his controller apart to see if he could tell if the relay had failed. The relay (which is located on a circuit board even though it pulls all the amps that the rear blower does) had come loose from the big solder land it sits on on the circuit board. He re-soldered it by hand and it works great. Since then, many others have also said that they have successfully resoldered their relays. So try this.
Here's a picture of the circuit board. You can see the blackness around the right-hand solder connection where it has failed (top right, circled).
Hmmmm, doesn't it seem that the resoldering of the relay may be just a temporary fix? Why wouldn't the current flow that causes the original failure not just create a second failure? (Of course, now we know how to repair it!) Turns out that not only is this probably correct, but there is a second type of repair that might be a permanent one. Michael Licitra provided the insight:
A little more info on this topic from a circuit board design point of view. Based upon the great photos, it is apparent that the cause of the failure of the circuit is the inadequate size of the circuit board trace from the landing pads of the 8 GA wires to the relay terminals. The + terminal is broken and happens to be the smaller of the two traces. The large current draw is overheating the copper trace and it loosens from the circuit board substrate - well you know the rest.A better remedy to this situation is to increase the effective conductor size to the relay by placing a short jumper between the landing pads of the 8 GA. wire and the relay terminal on the underside of the board. This will give the current an alternate parallel path and reduce heating because of an overall larger equivalent conductor size. Simply resoldering the board will remedy the problem only if a lot of solder is used and bridges the conductive path to the relay and landing pads. A better solution would be to install these jumpers to increase conductor size.
I mentioned this in the Villager mailing list and Marco couldn't help himself... :-)
Could not resist to try the jumper wire approach. Easy to perform, but you do need a soldering gun that has enough oompf. Mine is a 100 Watt and that was barely enough.
Here's a closup picture of Marco's repair:
So there ya go!
THAT should be a permanent fix!
Dsc09090-.jpg, Dsc09091-.jpg, Dsc09092-.jpg, Dsc09093-.jpg, Dsc09097-.jpg,
Dsc09099-.jpg, Dsc09100-.jpg, Dsc09101-.jpg, Dsc09102-.jpg, Dsc09103-.jpg,
Dsc09107-.jpg, Dsc09111-.jpg, Dsc09115-.jpg, Dsc09116-.jpg, Dsc09117-.jpg,
Dsc09119-.jpg, Dsc09122-.jpg, Dsc09123-.jpg
Here's the before picture: badsolderjoint.jpg
Here's David's beautiful repair: solderedjumpers.jpg
