Switching a fan to full on?

I been searching around and have been unable to find a definate answer. I would like to be able to switch the engine fan on at my desired time if i so choose to. How is the duty cycle controlled is it ground swithced so i can just put a switchable ground to that wire. Will it back feed and piss the pcm off?

Anybody done this?

Thanks Travis

I like to know as well

Me too!



Sent from my iPhone using Tapatalk with fat fingers so excuse the typos!

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I dont know on the newer SD's but the 99-04 is a mechanical setup with a thermostatic clutch. It is a temp based setup, I dont think there would be anyway to change the on/off cycle. They do make electic lockup clutches that would allow you to have an over ride switch to force the fan to come on when desired. Many times they come in the MDT trucks, you might check with a fleet company for more info.

6.0 have a electronic variable lockup clutch

Grounding the dark blue wire will lock up the fan clutch.

with no ill affects to the pcm?

Thanks Travis

Couldnt tell ya what long term effects it will have, I just do this momentarily to test the fan clutch operation.

Hmm so i guess i might get to be the guinnea pig

I can tell you this, If you lock up the fan hub up solid on a 6.0 above about 2500 rpms the belt will start howling because the fan is so big. i had do do this one time when the wiring got pulled out of the fan hub

I been curious about this also, what if you used a diode so the ground would never back feed to the pcm. Then a person could flip a switch to lock up the clutch at anytime. I dont like waiting till over 200 for it to lock up.