Andrew

But then, I traced the circuit and found the control signal passed through a small component also mounted to the heat sink, which I couldn't identify. So on a whim, I shorted across this component... and my fan started running!

My best guess is that this component is a thermal cut off switch. Built to burn out if the heat sink gets too hot. (Now, they could have put in something with a reset button, but then they couldn't sell an expensive replacement part.)

I decided to replace the unknown part with a 10 K ohm resistor. It works with the new Mosfet just like new. I don't know if the original Mosfet was even bad... probably just the 'strange' part burned out. But since it is working, I didn't bother swapping back the old part to test it.

I'm going to look to see if I can find a replacement thermal cut-off component, but until then... it works!

Here are the steps:
1. Follow the excellent pictures from Solara's post to remove the fan amp.
2. Remove the white plastic cover from the fan amp.
3. Unsolder the 3 connections on one end of the circuit board and the two connections on the other end. (Melt the solder while gently lifting the circuit board and work your way around making a millimeter progress or so at each connection until all are free.)
4. Remove the screw holding down both components to the heat sink.
5. Remove the 'strange' component (the one with two leads).
6. If needed, replace the Mosfet... you may not need to. If you do replace it, use thermal grease. The whole heat sink gets REALLY hot... you want good conductivity. You can probably get thermal grease from Radio Shack.
7. Tighten the screw back down. If you replaced the Mosfet, you may need to add a washer, as the replacement part is physically smaller than the original.
8. Solder a wire or a resistor (0 - 10K ohm) onto the circuit board at the two-connector end (where the 'strange' component was removed). The resistor need not be physically mounted to the heat sink as was the 'strange' part.
9. (Optional) solder short insulated jumper wires to each lead of the Mosfet, so if you need to disassemble this part again you won't have to repeat the pain of going through step 3.
10. Solder the 3 Mosfet leads (or the jumper wires) back onto the circuit board.
11. Reassemble and mount back in car.
12. Better change out the filter (again, see the pictures above), since the clogged filter probably caused too little air flow, which caused the fan amp to overheat, causing the thermal fuse to blow in the first place. (I think I'll try using some material from a home furnace filter, under $2, stuffed into the original plastic frame rather than pay $20+ for the replacement part.)
13. Test it out... hope it works for you!
14. Legal disclaimer... how stupid that lawyers have forced us into this... the 'strange' part may be crucial to the safe operation of this system. By removing it, you may be placing property and perhaps lives at stake. I do not know the original purpose of this part. Its removal may burn out the whole electronics section of your car. It may allow the fan amp part to overheat and melt the surrounding parts or even start a fire. It may void your vehicle's warranty. (If you believe in chaos theory, it may cause world war 3.) Concern over these effects could raise your blood pressure and perhaps cause a heart attack and possible death. On the other hand, it may just work.

I've never heard what you've been told. In fact, when mine went out in my truck (an '01 QX4) about 3 months ago, I took it to the dealer (it's under an Infiniti extended warranty) and they just replaced the fan amp.

My opinion is that unless your truck is under warranty, which it doesn't sound like it is or you wouldn't be here, you should just replace the fan control amp. yourself and save a few crisp hundred dollar bills.

Andrew

Thanks again!!!

Billy

http://www.nissanhelp.com/Owne...7.htm

-or-

http://x.nissanhelp.com/forums...age=4

I replaced the failed component within the metal case (making sure to properly re-heat sink the replacement component since all fan motor current is driven through this small part). You will have to solder the part into place, but there are only three pins on the part, so it's a fairly easy repair. The repaired amp module has worked perfectly fine. We haven't had a problem in over a year now. The replacement component costs about $3.

That takes the repair of this problem from a $700 dealer repair, all the way down to a $3 component replacement if you are willing to get out your soldering iron. Use the directions from another author in this thread to remove the AMP module metal can (The pictorial instructions provided in this thread are excellent). Then open the can and find the only part that looks like the one pictured in the link below.

A link to the replacement part follows:
http://parts.digikey.com/1/par....html

This fix took the $700 dealer repair beyond the savings of going with the $120 module replacement - all the way down to a $3 component replacement.

By the way, there is also a thermal fuse in the module. Mine checked out ok with the ohm meter, but I replaced it also anyways since I had the module opened to replace the MOSFET. The part number I used for that component follows:
http://parts.digikey.com/1/par....html

I hope others can have the same success in savings I had with this repair.

Andrew

Good luck,

Andrew

Andrew

I have a 2003 Pathfinder and bought the parts at Courtesy. Delivery slower than I would have liked, 4 business days, total cost for fan control amp and filters was $156, delivered. The 2003 Pathfinder is also one of those where you have to cut out the hole for the filters. If I had done my homework and realized this ahead of time I would not have installed them. Trying to cut a clean hole in the plastic so that the filters fit nicely was a PITA. I have done without them all this time could have continued without them. Unless you have severe alergies or other reasons to want them I suggest doing without.

Also, when I ordered the Fan Control Amp I also purchased the cabin filters. There are no provisions in the housing to accomodate these filters. I read in a previous post that it may be necessary to cut slots in the housing in order to use these filters. Is this indeed the case?

Thanks for all the great help so far.

Do you have the digital (automatic) heating/air system or do you have the three dial (manual) heating/air system? If it's the latter then the above paragraph applies to your vehicle. If it's the former, then everything I have said here does not apply.

The blower resistor is actually very simple to replace and only takes about five minutes and no dis-assembly is required! If you look under the glove box area you can see the blower motor. The blower resistor is located on the other side of the blower motor (on the firewall side) and it's held in with two screws. You just have to remove those two screws and pull out the blower resistor. Here's a diagram to help you locate it better:

If you have a multimeter you can test the terminal resistances to see if this is actually your problem.

Thanks so much. I just had the same problem with my 2002 Pathfinder a couple days ago. Thanks to your information here I fixed it today for just under $200 and about 20 minutes.

Another strange problem I have is that my car loses oil. It doesn't leak and there is no smoke in the exhaust. I found other sites saying it was a defective right valve cover. Have you heard of that?

Actually, there is another hard problem to diagnose. My dash lights are half out but not all the time. Most of the time my MPH is lit but my Tach is not. Then whenever it feels like it, the whole thing is illuminated. I have no clue where to look for that one.

I appreciate any insight you may have.

Thanks.

Anthony

Thanks for all of the help first.

I have a 2001 Pathfinder LE V6 and have had the same problems of my blower not working. Ther was no voltage to the blower motor. So as everyone had done I took out the fan amp and found in my case that the thermal cut off fuse was blown.

For everyone's reference the N-Channel MOSFET was an NEC K2500 9Z

The thermal cut off fuse is a Panasonic N-Series EYP2BN134. I had a lot of trouble finding them so I ordered:

Cantherm SDJ1 DF141S

Digikey Product Number 317-1134-ND

I just ordered this new thermal fuse and have NOT tried it out yet. Since the specs appear to be very similar it should work. I'll report back once I test it out.

By the way when removing the circuit board use a flat screw driver and pry up on the side where you can see the little screw holding the MOSFET down on the heatsink. The side there there is a single brass connector (labeled R1/R2). Then use a small screwdriver and remove that screw. The lift vertically up to disengage the thermal paste which is very thick in consistency.

Hope this help everyone. I'll report back soon.

My wife has an 05 pathfinder and the blower is working intermittently. It doesn't run when you first start or drive, but then about 15 minutes into your ride it usually starts working and works fine on all speeds until the vehicle is turned off. It has the digital controls and nav system, but I believe it is a "manual" blower fan system as from what I've read and the diagrams I've seen, I can definately see the resistor module with a 4 wire white clip going to it under the glove box on the passenger side next to the blower motor. However when I test the blower motor, I am getting 12 volts and power to it through the blue wire. Power goes away when I turn the fan off through the controls. So if I am getting power to the blower, then the resistor module should be working, right? Just not sure if I should change the blower motor or module and wanted to get some feedback.
Thanks!

I have to same issue ! I have to turn the air/heat on and off a few times before the sound stops. And sometimes it still doesn't stop. Def want to get this fixed before the winter.

I'll order the motor thanks to your post!!