Can Anyone Explain How This Could Possibly Happen??


2005 T1N Conversion
Yesterday, but not today, my Sprinter did something that baffles me. It goes beyond all possible logic in my head.

I have the blower fan for the heater/ac on #4. Full blast. I keep it there because that's the setting that still works.

So, I turn off the Sprinter at a gas station the other day and go to get out to pump some diesel and gasoline. But... as I go to get out, I hear something different. There is still a sound when normally the sprinter goes silent.

It turns out the blower fan is still on with the key turned off and removed!!!! It isn't blowing at #4 full power, even though that is where the dial is still set. It is blowing at like #1 or #2 speed.

So, i turn the key back to "on", the dash lights light up and the blower speeds back up to #4 speed. Turn off and/or remove the key and the fan goes to #2 speed instead of turning off!

All day this happened! Today, back to normal.

Can anyone explain how this is even possible??


There is a setting on the Heat system that will run the blower at a slow speed until the water in the engine cools to a certain level. it is called the Residual Engine Heat Utilization(REST) page 124 in the users manual. But, it has to be activated manually. Sounds like the Climate Control module is bad. Sounds like it has a mind of its own. I have a friend that has replaced his twice.


New member
That makes sense. I was thinking a stuck relay, but your explanation jives with reality.


2005 T1N Conversion
I was thinking REST system as well. I do have that option installed. Never used it.

However, the rest button was not engaged and the REST light wasn't on. Also, the air coming out was cold/ambient temperature. Prior, the air conditioner was in use. I'm in FL now.

Weird stuff!

Maybe the REST blower mode decided to engage all on its own? This would have killed a regular starting battery.


New member
possibly some chewed up wiring is making contact, bad ground, etc?


New member
Placing my money on goblins hiding in the dashboard ................

Either a defective control module or a relay failing to release


New member
The REST cycle should shut off around 30 minutes. Try cycling the REST pushbutton a few times to see if this makes any difference.



2005 T1N Conversion
The REST cycle should shut off around 30 minutes. Try cycling the REST pushbutton a few times to see if this makes any difference.

After cycling the ignition key to prove i hadn't gone crazy, that was the first thing i did. The REST button had no effect on the fan.

And... i can't try it anymore, since it only happened yesterday and never again. German Easter Egg? :)

The ”fan.death.772.exe" virus, set to make your fan stay on in early November? :)
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Erratic Member
I have had (in 8 years of ownership) a similar "one off" occurrence, about 2 years ago.
I parked, removed the key, and left the Sprinter (locking the doors remotely, as usual).
The dash display did not go off. It's possible the fuel pump was still running, too.
Not in its usual 20 seconds, not 60 seconds later ... it stayed on.
Entering/exiting didn't cure it. Starting/stopping the Sprinter did.
(i didn't try the blower fan)

In your case: do you have the optional 7-day timer? That will run the fan at speed 1, too.


Eric Experience

Well-known member
The answer is in your second line. The heater control monitors the voltage on the resistor string in your blower to determine if you are able to activate the A/C. If that resistor string is broken or the connector to it has fried the system gets confused. to fix it remove the resistor string and test it. Eric.


2005 T1N Conversion
Excellent, Eric!

What really baffled me was that it continued after removing the key from the ignition.

I thought that would cut the power to all computers, but apparently not...

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