Enabling full Fan (ATC) Power with Engine Off

vanski

If it’s winter, I’m probably skiing..
Enabling full Fan (ATC) Airflow with Engine Off

Seeing folks talk about their Espars and getting them to work with the engine off has prompted me to upgrade the one final item I'm not super happy about with my heater booster engine off configuration: Having full air flow through the ATC (fan) compared to about 33% per the REST functionality.

I did a variation of Wiring Heater Booster to run from Switch but my 12v source is a house battery (most folks following this write-up run from the starter) and I routed everything SPDT relays without feeding 12v into any existing lines to light the line up (the write-up calls for splicing into existing wires). In the write-up there's a step where you feed 12v into an unused plug above the shifter. It's step 6 found at https://sprinter-source.com/forums/attachment.php?attachmentid=772&d=1169427461

Has this approached worked for me.. Absolutely, and on my ski trips I wake up to a toasty van with warm ski boots. BUT, the problem with this approach is that it essentially taps into the REST ATC functionality which only gives me three settings of air flow; low, medium, high. Most importantly the high is about 1/3 as high of air flow as you get when the vehicle ignition is on and you turn the ATC dial to high (4). I want 3/3. I want 100%. Am I being unreasonable? :idunno:

I think I understand why Mercedes engineered it that way from the beginning; they wanted to limit the amperage draw folks were running so they didn't drain their starter battery.. Fine, I get it. But when I'm running my Espar for warmth I'm running from two 6v batteries (I might be going to 4 here shortly) in series which are completely disconnected from the starter battery and quite honestly it's not going to be the end of the world if I drain them. I haven't drained them yet....

So, I'd like to find the 100% power ATC line, route it through an SPDT relay, and have 100% ventilation capability. :rad:

Can anyone tell me where the ATC power line is that allows you to turn the fan on while the engine is running? Is there more than one wire for some reason? Has anyone worked through this or come across a write-up on this? I can't seem to find one.

As usual, thanks to all of those who contribute so much great information on this forum!

-Vanski
 
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vanski

If it’s winter, I’m probably skiing..
I might be getting closer, but these wiring diagrams are pretty Greek to me. In the technical document 2006-VA-SM.pdf, I think the wire I need to access is somewhere on page 8w-42-6 or 8w-42-7. I'm thinking it's the wire that goes into the Blower Motor Resistor Block, C224. I don't know what C224 means.. But the diagram is different from page 6 to page 7???
 

cahaak

New member
Your approach is correct. You need to ID the wire and supply 12V to it. If you have the wiring diagrams, you can maybe work backwards from the other wires and understand what you need to supply power to. The power draw from the fan on high is significant if I recall correctly from another post.

Chris
 

vanski

If it’s winter, I’m probably skiing..
Thanks Chris. The more I review the wiring diagrams and think about this, I think there's already 12v to all the wires, but the ATC module will not turn on (unless I activate REST or my Engine off heater booster config which only gives me 33% of airflow) until the ignition is in position 2/3. So there's some kind of ignition signal wire which is allowing the ATC to connect the RD/BL wires in the attached diagrams. I can't seem to identify that signal wire which allows the switch (ATC) to be activated.

Or, is that the RD/BL wire which does not have 12v unless the ignition switch is in position 2/3 and I just need to route 12v in via a relay right there? That should be easy enough to test..
 

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NetDoc

Member
I looks like your blower motor (on this diagram) is S209??? It's not really showing the fan, now is it? If 209 goes to the hot side of the fan, then you need to jump in at either #2 on C2 or #4 on the Blower Resistor Block.
 

vanski

If it’s winter, I’m probably skiing..
Thanks Netdoc.. s209 is making some sense when I look at page 8w-42-5, but when I look at page 8w-42-6 it seems like it just goes to the #4 (the DG (dark green wire)) pin on the fan blower motor resistor block. I've attached page 8w-42-5. But perhaps that puts 12v to all the 4 roller dial settings? And then I need to put 12v to s201 on the BK/BL/DG (Black/Blue/Dark Green) wire to 'trick' the ATC module into thinking the Ignition Switch Output is on??
 

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NetDoc

Member
You might be overthinking it. It appears that there is more than one way to power the fan. With the battery disconnected, I would ohm out the wire from the the #4 wire and the fan. It just might be your Huckleberry.
 

vanski

If it’s winter, I’m probably skiing..
You might be overthinking it. It appears that there is more than one way to power the fan. With the battery disconnected, I would ohm out the wire from the the #4 wire and the fan. It just might be your Huckleberry.
Thanks NetDoc. Most likely I'm completely over thinking this. Oh boy.. I did my heater booster project and figured out some stuff, but I'm still a novice hack. When you say "ohm out" do you mean check the resistance on that wire. I guess I'm still too green in my wiring experience to quite understand how that would determine if that's going to help.

The fan is going to be pulling around 30A on high.
I'll fuse it properly and have plenty of amp hours for this need when it arises.
 

NetDoc

Member
Ohm out means to check it for continuity. In other words you want to make sure it's the right wire. I would actually disconnect it from both sides in order to test the wire. There's a lot of logic there and it would be easy to test something you don't realise. Best to take it slow and be sure. Use the continuity setting on your DVOM if you have one.
 

vanski

If it’s winter, I’m probably skiing..
Ohm out means to check it for continuity. In other words you want to make sure it's the right wire. I would actually disconnect it from both sides in order to test the wire. There's a lot of logic there and it would be easy to test something you don't realise. Best to take it slow and be sure. Use the continuity setting on your DVOM if you have one.
I tested for continuity across the pins, think I got it. Decided to cut the Dark Green #4 pin wire for the Blower Motor Reisistor Block as seen on diagram 8W-42-6, wired it to 12v fused to 30amps... DID NOT WORK.

Observations:

+ Ignition turned to the #2 position - None of the 4 dial settings worked with the engine on
+ Ignition turned to the #2 position - For whatever reason the defrost which is essentially the highest level, did work
+ Ignition off - REST, None of the 4 dial settings worked
+ Ignition off - For whatever reason the defrost which is essentially the highest level, did work (weird)

Luckily when I crimped the #4 Dark Green wire back together everything worked as designed, pew.

In diagram 8w-42-6 it shows fused 30amp 12v coming from the RD/BL wire. But, the switch (not the rolling 4 switch, but the single) can not be closed until the solenoid is tripped via 12v from s201 via the BK/BL/DG wire. I'm thinking that's essentially a SPST relay there coming from the s201 circuit. Perhaps I need to put 12v on that BK/BL/DG wire (if I can find it) and then 30amp fused power to the RD/BL wire. Better yet, if I could just take out that SPST relay and replace it with a SPDT relay, it should work. But, I'm thinking it's not a standard relay and is probably embedded somewhere really hard to get to.

The BK/BL/DG wire from s201 should fake the signal from the Ignition Switch Output which will light up the solenoid which will allow the switch to be activated. Right team? :drink:
 
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NetDoc

Member
I haven't had the time to suss out the logic completely. There are two ways to control anything: by controlling the hot or the ground. Switches often control hots. Safety circuits and CPUs would rather control grounds. Just putting power to the fan does not mean the fan will turn on if the ground has been interrupted for whatever reason.

The real problem does not lie in playing with the switch side as 12V is 12V. The problem comes in trying to second guess and possibly harm the CPU on the other side. Work with caution. Mercedes tends to over engineer and that means over complicate. I can't believe that the lock/unlock mechanism works the way it does. Some of their decisions leave me shaking my head. I would hate for you to ruin something by accident. Keep posting what you've done and what has/has not worked. Good info.
 

vanski

If it’s winter, I’m probably skiing..
Thanks NetDoc. By the way, checked out your site.. Pretty cool stuff. It's been a while since I've gone scuba diving. I did recently go abalone diving up near Mendocino here in California. Lots of work!!

Perhaps check out my 8w_42_6_notes attachment.

My novice eyes read this to tell me:

+ 12v fused to 30amps need to come through RD/BL wire @ C2
+ The SPST relay (switch) is activated when the solenoid receives 12v from the BK/BL/DG wire @ C1

An easy way to test this should be to just find that wire located on the ATC module, cut it, fuse it to like 1amp since most solenoids only require like 200ma to activate, put 12v on it

I DON'T WANT TO FRY MY CPU! THAT SCARES THE :censored: OUT OF ME, SO PERHAPS I SHOULD JUST GET OVER THIS PROJECT
 

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vanski

If it’s winter, I’m probably skiing..
Well, the unfortunate thing right now is that it's only noon here in PDT and that's too early to have a celebratory cocktail for figuring this out. As usual, it was much more simple than I was making it out to be. :cheers:

I had one scary moment where I cut the fused ignition switch BK/BL/DG wire (@ C1 which is supposed to energize the solenoid and close the 30am 12v switch), put 3amps fused 12v to the ATC, and 'something' else kicked on and LUCKILY blew the 3amp fuse. I didn't try that one again to see what it turned on.

See my new notes diagram. On the back of the ATC there's a black wire leading from the SPST switch to the back of the variable 4 speed air motor switch. Unplug that. Take some 10awg or larger wire, fuse it to 30amps, put a female spade terminal on it, plug it into where the black wire was plugged into. Voila! You can now have full throttle air flow through the ATC with the engine off by bypassing the ignition solenoid and SPST switch. :rad:

NOTE: I think it's pretty important to put a SPDT relay in there so the ATC can only be turned on with a switch when the engine is off. The kids think The Beast is a space ship and sometimes go in there and roll the ATC dial. Even though this is hooked up to my house battery and I wouldn't be stranded if it was drained, I still would like to mitigate risk of it being unintentionally drained.

I've also attached a picture of the black wire (the terminal) and my red 10 awg wire with female spade terminal for reference.
 

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ECU

2006 T1n 118 Sprinter
You could feed that wire from your Aux battery to avoid draining the start battery.
 

vanski

If it’s winter, I’m probably skiing..
Vic:

Perhaps I'm not reading/understanding the diagrams properly. I clipped the DG wire and feed 12v to it, but would only get #4 (high air flow) to work. I did feed it directly into the resistor, which makes sense as to why that would be the only setting that would work. From my experience/efforts, what I learned was the 12v fused to 30amps needs to either come from C225 and then the SPST switch needs to be connected via the solenoid, or, you bypass the switch and put the 30amp fused 12v directly into the ATC module at the black wire I identified. I couldn't figure out how to activate that solenoid via the BK/BL/DG wire coming into C1, thus I went the route of bypassing the switch and installing my own SPDT relay hooked up to my 7 day timer relay coil bus to act as the switch. Going straight to the 'source' worked for me, but I would like to hear a success story of activating the solenoid and putting the 30amp fused 12v source through the RD/BL wire at C2.
 

vanski

If it’s winter, I’m probably skiing..
For anyone doing this upgrade, one problem I did run into after doing this upgrade is there's a small metal clip behind the ATC circuit which rubbed against the non insulated OEM black wire female connection and shorted. I ended up ripping the entire ATC unit out again to properly insulate that connection to the relay. If you're the type of person who does everything right the first time, this post doesn't apply. When I finally got this to work I skipped properly insulating that wire and paid the price down the road!!!
 

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