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Blower is 100%. AFTER A NEW RESISTOR

4052 Views 19 Replies 7 Participants Last post by  Yah Reigns
2009 Frontier Pro-4X CC SB.

- Fans started blowing full after 45 minutes of driving (This sucks)
- Disconnected the Resistor and the fans stopped
- Ordered a 4-fin replacement (Part here: More Information for BECK/ARNLEY 2040097)
- After received, tested it hanging in the passenger foot well, and the dash controller worked like a charm again
- Bolted it into place, retested, and it's all good
- The next morning, I drove the car for 2 minutes, turned on the blower, and it went full blast again, and had to disconnect the new unit.
- Got another resistor from a junk yard, and it immediately put the fans to 100% as well.

I feel like something upstream of the resistor is out of wack.

Any advice on this annoying issue would be greatly appreciated!
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Forgot to mention the unit I got from the junkyard. The second I plugged it in, it went from room temperature to scalding hot in 2-3 seconds.
Really amazing how how it got.

Looking @ other forums, I think it could be a bad ground, or the blower motor itself having trouble turning.

Truck has ~155,000mi on it as of now.
I feel like both of your issues were the fan NOT working.

My issue is the exact opposite. It is FULL BLAST no matter what.
I will still investigate the fan & relay tho.
No - my fan would work on 1 and 5 only - they were both buggered after going through some deep water.
Even so, if the fan knob on my dash is in the "OFF" position, shouldn't the fans be off?
Currently the fans are on "high" no matter where the dial on the dash is set to.
If I recall correctly some had the back of the control panel melted or other similar type damage.

Yeah, i've read that a few times here and there. Do you happen to have a link to any of those threads?
OK, new approach was to perform the Front Air Control Self-Diagnosis.

Only light that stays on is the "Intake" which points to a "Mode Door Actuator" failure.
I got under the dash and the door seems to function perfectly. Very smooth and fluid. I remember replacing something in that area about 6 months ago.

That wouldn't explain the blower fan being on all the time tho.
OK, I removed and inspected/tested the resistor, relay, fan, and control unit.

- Visual: No bulges on any of the 3 units. No burn marks or other wear on any of the 3 units
- Voltmeter readings(ohms):

- Brand New Unit:​
- Pins 1-2: 0​
- Pins 1-3: Open​
- Pins 1-4: 40.6k​
- Pins 2-3: Open​
- Pins 2-4: 40.6k​
- Pins 3-4: Open​

- Junkyard Unit:​
- Pins 1-2: 0​
- Pins 1-3: 0​
- Pins 1-4: 0​
- Pins 2-3: 0​
- Pins 2-4: 0​
- Pins 3-4: 0​

- "Failed Unit":​
- Pins 1-2: 0​
- Pins 1-3: Open​
- Pins 1-4: 38.8k​
- Pins 2-3: Open​
- Pins 2-4: 38.8k​
- Pins 3-4: Open​

- Visual: Looks brand new, no corrosion, contactor close fluidly.
- Continuity: Paths are open when contactors are open. Paths are closed when contactors are closed.

- Visual: very minor rust @ end of shaft. Spins freely, no binding or resistance anywhere

Control Unit:
- Visual: No wear at all. No shorts observed.


Control Board Front:

Control Board Back:

The three resistors:

The Pin out for Voltmeter readings:

I haven't a clue what' causing this. Would a fuse be blown?

I really need to get my hands on the wiring schematics for this part of the car, but can't find them from searching around...
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Yup. Been working through the HAC section for a few days.

Pretty sure I have a short to ground at this point.

I got a new unit from Beck/Arnley from Rockauto and tested it with a multimeter vs the blown and OEM units.

There are 2 connections that showed differences in resistance from the new to the old.

I plugged the new one into the truck, and turned the accessory on, VBC works like a champ for a few minutes. I turned the ignition on, and again the VBC keeps working perfectly. Then i turned the ignition off, and turned it back on, and the VBC was blown.

So something happened when turning off the ignition that caused the VBC to fail.

Any ideas?
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I would suspect one of several things.. The blower fan motor is drawing too much amperage and when you turned off and back on, the draw caused the VBC to blow. I remember years ago (I think it was in the early '90's), Nissan had a bad run of blower motors that were drawing excessive amperage and burning out the blower resistors in the Sentras. Less likely, I would consider a poor ground circuit for the VBC or a faulty HVAC controller. If I was going to replace the VBC again, I would definitely install a new blower motor, as well.
As soon as you said that it made perfect sense. Wiring harness checked out. Relays. Fuses. Etc.

I got a new VBC from Rockauto, and in the box, there is a small note that basically says "The most common reason for this part to burn out is that the fan has gone bad and now draws more than 10 Amps. You must ensure that the fan draws under 10 Amps before installing."

I placed the new fan and the OEM fan in the engine bay with some gator clips and a multimeter. I hooked them up and watched the flow.
OEM: Spikes to 10.6A, tapers to 8A
New: Spikes to 9.3A, Tapers to 6A

New VBC + New fan solved the issue.

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