Hey guys - anyone ever had a problem like this? I tried doing a search, with no luck.

I turned on my A/C the other day, the fan went full blast and wouldn't slow down or shut off, no matter what I did (slow it down, turn it off, etc). I tore my dash apart, disconnected the plugs to my automatic climate control, and it still goes full blast. ???????

 

Although it might only be a short term solution, unplug the battery negative, wait 2 mins, and reconnect.

If the problem still persists, I would recommend replacing the relay. I think that the relay may be stuck in the closed position.

 

Thanks, I tried disconnecting the battery - no luck. Any idea where the relay/module is located? I haven't found it, and no repair manual lists its location.

 

I don't see how a failure of the relay could cause the fan to run on high speed. If the relay failed open the fan would not come on at all. If the relay welded itself closed the fan would run with the ignition off. But if the relay were stuck closed, the a/c controller would still be able to modulate the fan speed when the ignition was on. The relay is switched by the ignition switch, not by the a/c controller, so the fact that the fan runs even with the controller disconnected does not really prove anything. If the fan shuts off when you turn off the ignition, then it's probably not the relay.

Most likely what has failed is the "fan amplifier." This is a transistor switch that takes a signal from the a/c head unit and controls the fan speed. It is located in the a/c supply plenum more or less above the passenger footwell, just downstream of the fan. It is possible for this to fail either open (fan won't run) or closed (fan runs full speed.) Sounds like your winning ticket was the latter.

Also could possibly be a failure of the control unit. If you look around on this forum a few people have posted the procedure and how to interpret the results for the self-test of the control unit but depending on exactly what part has failed, this may or may not be useful.

I'm not sure but I believe that if you disconnect the input wire of the amplifier it should shut off the fan. If that is right, then the fact that the fan kept running when you unplugged the control head does indeed suggest the fan amplifier is the problem.

Also possible but not likely would be a short to ground on the negative side of the fan, or a short to a +12 supply on the control input to the fan amplifier. (which would either be caused by a blown control head, or would result in a blown control head.)

 

try procedure shown here:

http://forums.maxima.org/showthread....ds#post4248498

and go to... menu '4'

41 will be 4-5V for the blower, 42 will be 9-11V, 43, 44, and 45 will be 7-9V, and 46 will be 10-12V

the amp controls fan speed by varying the gnd signal to the blower motor, based on what the control head inputs to it. i can email you a wiring diagram if you like

 

Thanks for the help guys. It seems to be the Fan Amplifier - I've ordered one and I'll post results.

 

Yep - the fan amp was the problem. Nissan parts called it a "Power Module" - P/N 27761-2Y000. Thanks again

 

cool, good to hear its fixed...

 

Ahh, the drama continues....
The fan quit working after a day - I started digging further and found the brearings in my fan were toast(even though it wasn't making any noise). The fan would pull too much current, which probably made the fan amp blow up. As an FYI to anyone else out there with this problem - you might want to check your fan if the fan amp goes out - could save you a few $$ for your time.
For you electronics wizards out there - the chip in the fan amplifier is a NEC 2550 56, the thermal fuse is rated for 2A @ 140 degree C. Everything else looks like it could be found off the shelf at Radio Shack.

 

Is this fan amp used in lieu of a blower motor resistor on our cars or do we have those also?

 

You're correct if you have a manual fan switch. If you don't have automatic climate control, you don't have a fan amp.

 

it didnt toast the new fan amp, did it?

 

Well, I kinda lucked out - the thermal fuse blew in the new fan amp, the IC chip went in the first one. So, I combined the working parts out of the two into one, and it's running fine now. Hope it stays that way....

 

lol...


thats good, i guess


how much were the parts?

 

The Fan Amp ran about $90 from the stealership - I wasn't successfull finding the individual components. It's a shame 'cause there couldn't have been more than $12 of worth of parts in the thing.
I managed to find a heater blower for $25 from a local junkyard. The dealership wanted $250 (yikes!)
If it happens again, I'll probably just go to the junkyard for all the parts...

 

For anyone doing a search looking for good replacement / service info on heater blowers or fan amps, check out this other thread:

http://forums.maxima.org/showthread....15#post4971815

 

hey i have a 96 maxima the problem i have is that on my climate control first three fan speed switch doesn't work but the fourth one does i dont know if i should replace the whole climate control unit or what? please help me out if you can i would really appreciate it i have a manaual climate control you can email me the answer too at junnah9009@yahoo.com thanks alot