REST/Booster Engine Pre-heat with DPDT Switch Modification
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Edit:
In case there is anyone who reads further down and begins to question whether this circuit will work...
The DPDT Switch circuit I designed and provide in this post will work as advertised. Any discussion further on in the thread is related to overall circuit details and trying to understand all the MB OEM control logic. The DPDT switch circuit combined with REST is a simple solution that works as intended.
Added:
A basic outline for the physical installation has been added. Post #47.
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My original circuit using a switch and a diode for REST engine pre-heat works, but it has some flaws in that it can backfeed 12 vdc into some other circuits connected to Splice #362. For a basic optioned Sprinter like mine that is not a problem. For Sprinters which have things tagged on to the Optional Equipment Relay it can have some negative effect. (Not necessarily serious, just a nuisance.)
Realizing that, I looked for another option. After a couple different solutions I developed a circuit that uses a common Double Pole Double Throw DPDT switch. This new circuit prevents any 12 vdc backfeeds and should also address the ABS module pre-start check glitch.
Edit: If it doesn't cure the ABS pre-start check fault/glitch the response is fairly simple. Just turn off the DPDT Switch and REST before starting. Should you forget and get the dash warning lights, then shutting off the engine for re-start will clear the faults. Just leave the key off for 15 seconds for the ECM relay to power down. If you don't wait long enough for the ECM relay power down the ECM will remember the faults and display them again upon re-starting.
Most of the connections are found in the dash area on the ATC Module. I know that running a 2 conductor cable from the DPDT dash switch to the BK/BL/DG wire Espar Pin #6 at the Booster will work. That BK/BL/DG wire
may be available in the area of the dash to cut and connect. Using the documentation that I have available to me I was not able to determine if that is a practical method or not.
With the DPDT switch in "Normal" position (as shown) the REST and Booster Heater function per OEM design. With the DPDT switch in "Pre-heat" position REST powers up the DG/RD wire Circulation Pump which also enables the Espar heater. This allows approximately 30 minutes of pre-heat operation until REST times out.
Here is the basic circuit shown on the Booster Heater Diagram.
View attachment 128327
This is the original diagram without the notes.
View attachment 64539
Presently my switch and diode arrangement does what I need for my engine pre-heating. I don't plan to change over to the new design. That said, the newer DPDT switch circuit modification is the better choice.
vic
P.S. - Some PM's with Mortarsprayer got me back to thinking about this modification.
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Some Information Related to the Circulation Pump
Recently I have unraveled more information regarding the Coolant Circulation Electric Pump.
After looking at the documentation related to the MB Sprinter Aux. Electric Coolant Pump it appeared to me that either the description in the Service Manual or the schematics are wrong. So far the schematics are the most accurate, but maybe not 100%.
The schematics show the Coolant Pump to be basically fed by 12 volt sources which are subject only to the key position There aren't any fancy logic controls shown in the schematics. Maybe those fancier controls are on other MB models?
Based upon the thoughts mentioned above, I installed an indicator light to monitor the 12v power to my Electric Circulation Pump. It was fairly easy because my DIY Booster run with diode modification gave me an easy tap point in the fuse holder. My conclusion is that my pump has 12v power subject to the key. In the case of my 2004 with OEM Booster Heater, the circulation pump runs as long as the key is turned on or the engine is started/running.
I've tried many different operating conditions. So far the circulation pump runs 100% the time.
This is what I found with my Booster Heater aka Except Program Timer unmodified OEM controls/Circulation Pump testing.
My test light shows that the pump runs 100% of the time.
Nope. The pump runs 100% of the time.
Nope. The pump runs 100% of the time.
Nope. The pump runs 100% of the time.
Nope. The pump runs 100% of the time.
Unable to test above 230F, but the pump runs 100% of the time..
From my testing so far it appears that the pump running all the time as shown by the Service Manual schematics is the most accurate.
View attachment 64543
View attachment 64418
As an additional check I removed my DIY Diode Run fuse to test if the Espar Booster would run while the engine was off. I powered the Pin #7 with the DIY SPDT dash switch. The Espar did not respond at all. I set the ATC REST control to enable (DG/RD powered from ATC Pin C1-2 - Circ Pump Running) with the DIY SPDT dash switch still on. The Espar didn't respond at all.
I replaced the DIY Diode Run fuse. The Espar heater fired up.
Basic Conclusions:
The Coolant Circulation Pump runs subject to the key position as shown in the 8W-42- 09 schematic. There is not a circulation pump complex logic control with my Booster Heater option.
The Circulation Pump is not automatically powered up with the Espar Pin #7 enabled. (Espar wouldn't fire with only Pin #7 energized/enabled)
The Circulation Pump is powered by the ATC C1-2 pin DG/RD wire to run during the REST operation. (Splice #362 isn't in the path.)
The wire DG/RD being powered does not backfeed 12v to Espar Pin #6. There must be a blocking diode for the Booster Heater as shown in schematic 8W-42-09. The correct control wiring/logic is likely what I show in blue.
For the Espar Booster Heater aka Except Program Timer to operate 12v power must be supplied to Espar Pin #6 (enable). For the Espar Booster Heater that 12v is supplied to Espar Pin #6 via Splice #362. Splice #362 also supplies the Circulation Pump. If power to Espar Pin #6 is interrupted the Booster Heater will power off. That is regardless of whether the engine is running or not. That is another fact which supports that the Circulation Pump must be energized 100% of the time for the Booster Heater to operate.
As an aside, Splice #S362 is listed as "Near Circulation Pump Diode" Fig. 18. Under Driver Seat.
View attachment 64419
I haven't located the diode on my 2004 yet.
Please note that the circulation pump information above is derived from testing performed on one OM647 Booster Heater equipped Sprinter and doesn't necessarily apply to the Dash Inset Control aka Program Timer units or possibly even other model/optioned Sprinters.
vic
Added:
What turned in to a rather long and meandering thread with additional Espar information for my 2004 is here. (Anyone can feel free to condense and re-post any important stuff there to another thread.)
Some 2004 Espar Heater Notes
https://sprinter-source.com/forums/showthread.php?t=30384
There are other Espar threads in the T1N Database section.