nitis

I have only noticed this since it has gotten colder but seems to not be right after I start my truck and turn on the heater all the way and fan all the way It never stops but cycles up and down and tonight was the first time I have driven it when I needed headlights and heat and noticed that as the fan cycled up and down the headlights went slightly dim and then bright antone else have this experience?

Also another annoyance I have is when I am going down the hwy and run the fan at full throttle ac or heat I get alot of wind noise from the dooor somewhere turn down the fan it goes away anyone else is there a fix or am I going to have to live with it havent had that since my door sagging 85.

DrDiesel

The surge/cycle is from the heater grid. NORMAL.
The whistle noise is due to an air leak from a seal or weather strip.

nitis

I figured that was where it came from but is it worth mentioning to the dealer or am I going to get a blank look oh wait it does not matter what I ask them I get that look any way is there a fix for it or am I going to have to live with it.

Heater grid must draw some serious juice sure it is ok never had my lights dim before just want to get all I can my 36k is almost half gone

DrDiesel

Positive. It`s a (edit)100Amp circuit and will draw the volate gage down to 8 volts @ idle.

gRahAM Diesel

i had the same whistle on my 05 with the sliding rear window. If it was not seated just right it would whistle with the AC on high. If you have the slider just try opening and reclosing; its worth a try! I opted to not get the slider on the MC, hell I cant reach it anyway.

nitis

its not the slider its the driver door but I wish I did not have the slider wish I head the defroster instead

nitis

so it sounds like I have a logical answer but has anyone else experienced this surging?

gRahAM Diesel

yes. and as Dr. Diesel explained above it is a result of the grid heaters. Common to every 3rd gen when engine is below set trigger temp.

torquefan

Actually there are two elements that draw around 100 amps EACH. On the preheat cycle (before you start the engine) they will both come on together. On the post heat cycle (when the engine is running) they will come on one-at-a-time. The surging is normal, as this huge draw will drop the system voltage quite a bit. As the voltage drops, the blower will slow down and the lights will dim.

FMB

Yup, what torque said. The grid heaters should quit cycling once the engine is warmer or after you hit about 18MPH.

jpfishmaster

Yup, heater grid. I got worried before I knew about is as well.

schv

I'm glad I read about the grid heater cycling function here back before I took delivery of my new truck - I would have flipped out the first time it happened!

BRKN_Viewfinder

Thanks for the post guys. This is my first winter in my truck and the surging and voltage drop was freakin' me out. It actually tripped my engine light one morning when I left the beast idling to warm up in below freezing temps. Seems fine now, light went out.

Yellowlab

Trust what they're telling you! It is just the grid heaters and is COMPLETELY normal. It'll quit doing it as soon as you get it warmed up a little. You might consider having the manual high idle enabled. It helps warm your truck much quicker during the cold weather, and is much better for the engine if it'll be left idling for very long.

DiEseLjunKy

Mine does the same thing. Turn the ac fan on high and there's an annoying whistling noise next to your head on the driver's door. Turn it down just one notch below full blast and it goes away. Really odd. Its almost as if turning the fan on high makes the window start leaking air from outside. I know it sounds stupid but thats what it seems like.