If I listen for them I can hear mine in the cab with no radio on. Barely. Mine are the OE.

 

I have an LED that comes on when the PCM commands the efans on....(doesn't necessarily mean that they're running, as they wouldn't if they were un-plugged or something) but it illuminates when the PCM grounds pin 42

 

im getting ready to wire up a new set of efans with the nelson harness, can you post a how to of said LED and wiring??

 

I would think something as simple as a keyed hot wire to one wire of an led. The other wire goes and taps in with pcm pin 42. Not sure how pcm safe that is? I would take the time to hit the power wire after the relays, so you know there running. The other way just means there commanded...

 

[QUOTE=1998chevy1500;4179524]Just wondering if anyone knows why there are differences between these two 05+ efans.

The 5/7 blade fans are from the 05 and 06 trucks, the 7/7 blade fans are from the 07 and 08 NNBS truck. I am not sure of any installation differences but the 05 type comes with GM part no 15244099 while 07 type comes with part no's 3115209/210/211/212/213 depending on the body style and whether it has pf program

 

It's real easy, 12v goes to the + side of the LED (you can get the 12v pretty much anywhere that's convenient, I went with a key on 12v source, just can't remember which one), then the ground side taps into the wire going to pin 42 of the PCM. When the PCM grounds pin 42, it also provides the ground to turn on the LED. It is PCM safe, as it's only a ground circuit and not a sensitive millivolt circuit. I bought the LED at Radio Shack, just a run of the mill red 12v LED.

 

Knowing GM I would be willing to bet that the housing and motors and exactly the same and the fan/blades are the only difference. One would assume that the newer design is “better”.
I’m using the two pin setup and have two leds wired in so I can also tell if they are on high or low. If you go with two leds its best to use two different colors for night time clarity.

 

Yea, I'll bet that the only difference is the number of fan blades...

 

What did you install yours on? I am trying to see if the 7/7 version will bolt up to any of the NBS trucks like the 5/7s already do.

what is "pf program" ?

 

Got another curious question for those of you with the 05+ efans.

A common complaint I hear about these fans is the voltage dip that is present on their startup due to the large amount of current they draw when they first start spinning. My question, is this voltage dip only noted when the fans go from stopped to low speed? Or is it also noted when the fans go from low to high speed? Is there any situations where the fans go directly from stopped to high speed? (I would think that this would be a PCM thing, like maybe during certain conditions of engine temp and A/C usage)

The reason for my question. I was thinking to myself that if someone were to replace the far right relay (see schematic below) with a power mosfet and were to modulate that mosfet with PWM (pulse width modulation) from 0% to 100% over the course of say 3-5seconds in theory you should be able to greatly reduce the massive startup surge due to the current inrush. Of course replacing that relay would only give you "soft start" for the low speed, it would do nothing for high speed. But, if the current surge from low to high is small enough, or the usage of high speed is infrequent enough, you wouldn't really need to care about applying PWM to the high speed setting.

I have some very preliminary thoughts in my head of how to do this, but not having efans or any of the parts to test it means that it will probably remain just thoughts in my head until then.:nunchuk1:

Anyway fill me in on what you see in terms of voltage dips when the fans turn on and we can go from there. Also please include info like alternator size, electrical mods, etc.

Thanks