REST/Booster Engine Pre-heat with DPDT Switch Modification

Aqua Puttana

Poly - Thread Finder
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.

********************

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. (If the red text isn't visible at the bottom, scroll further down for the complete image.)

10.3.3 BoosterPreHeatRESTrev2e.jpg


This is the original diagram without the notes.

10.3.3 Booster.JPG


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.

*******************************************

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? :idunno:

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 information was copied from the service manual. It should answer your question about the pump operation.

DESCRIPTION
The electric coolant pump is used on all vehicles. The pump is located in the left side of the engine compartment near the battery.

OPERATION
The pump is controlled by the ATC control module and is only operational under the following conditions:
This is what I found with my Booster Heater aka Except Program Timer unmodified OEM controls/Circulation Pump testing.


Service Manual said:
(1) Vehicle speed below 27 Km/h (17 mph).
My test light shows that the pump runs 100% of the time.

Service Manual said:
(2) Coolant temperature above 65° C (150° F) but less than 110° C (230 ° F).
Nope. The pump runs 100% of the time.

Service Manual said:
(3) Any blower speed setting.
Nope. The pump runs 100% of the time.

Service Manual said:
(4) Temperature heat setting above the halfway setting (60% heat).
Nope. The pump runs 100% of the time.

Service Manual said:
(5) The pump will turn off at speeds above 48 Km/h (30 mph).
Nope. The pump runs 100% of the time.

Service Manual said:
(6) The pump will turn off if the coolant temperature rises above 110° C (230 ° F).
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.

8W42-09 wNotesRev2a.jpg

8W11-34Rev1a.jpg

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.

8W91-31-S362Diode.jpg

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.10.3.3 BoosterPreHeatRESTrev2e.jpg
 
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Aqua Puttana

Poly - Thread Finder
Hello Vic,
With this modification what do you need to do to reset the time and heat for another 30 minutes after the rest timer kicks it off? Can you do this by turning your switch off/on?

Thank you,
Nolan
When the REST times out the red indicator on the REST switch will extinguish. Pushing the REST button should start another 30 minute REST cycle.

It is possible that you may need to wait a short time for the REST circuit to reset before initiating another REST cycle. That is less likely given the solid state timing circuit.

vic
 

ECU

Well-known member
My 2006 has no diode. The diode is in the relay section under the seat and is round. I just don't have that in my setup. I have a basic sprinter, hand crank windows and no locking doors.
I finally have replaced my pump and espar and have the system operating. I notice much better heating just from having the pump work. Last winter, almost froze the windshield over while driving.
I assume that the REST button turns on the pump with key off. So the only thing holding back the Espar firing up would be the connection from the Rollover Switch Assembly. Since that Rollover switch is in the line, I think I would have to feed the supply after that switch. It would be VERY COOL if I could get the setup to be choosing both REST and the aux heat together to fire up the heat as we both want. No new switches.
What happens if Fuse #7 were powered while the key is off?
I also assume that the main power for the Espar comes from the Red #1 since that is a 20 amp fuse. I could feed that from the Aux battery all the time.
 

Aqua Puttana

Poly - Thread Finder
First let me say that my ideas on what is really going on with my Espar Heater OEM MB modified, not original Espar Booster unit controls change as I find new information. The way they squeeze multiple control schemes into the documentation tends to make the MB schematics confusing at best.

One needs to pay very close attention to the notes and references to Program Timer, Except Program Timer, Cabin Heater Module CHM, REST System, Heater Booster Module HBM, and probably some others which I'm missing.

My 2006 has no diode. The diode is in the relay section under the seat and is round. I just don't have that in my setup. I have a basic sprinter, hand crank windows and no locking doors.
I have the same basic Sprinter. There is no diode under my seat either.

There is also no Fan Stage #1 Relay or Circulation Pump Relay under the seat for the Booster Heater option. That is consistent with the MB documentation.

It makes sense that the Splice #362 with 2 each BK wires and BK/BL/DG would be located under the seat with the 2 relays mentioned above a;ready being there for the Program Timer unit.

A very close inspection of the electrics under my seat show no diode. I can't find Splice #362 either. I did trace the Circulation Pump DG/RD wire through the firewall into the dash area. I didn't find that wire heading to, or under the seat.

A specific reference to a diode for the Booster Heater is indicated in some schematics. With no Stage #1 Fan or Circulation Pump Relay under the seat, it would be logical for the Booster System diode to be located in the dash area rather than under seat. I have not dis-assembled my dash to search for a diode. Tests which I have done on my Circulation Pump circuit lead me to believe that there is a diode (if it is wired to Splice #362 as the schematics show *in general*).

https://sprinter-source.com/forums/showthread.php?p=331039#post331039

I finally have replaced my pump and espar and have the system operating. I notice much better heating just from having the pump work. Last winter, almost froze the windshield over while driving.
The pump runs 100% of the time on mine.

I assume that the REST button turns on the pump with key off.
That is correct.

So the only thing holding back the Espar firing up would be the connection from the Rollover Switch Assembly. Since that Rollover switch is in the line, I think I would have to feed the supply after that switch.
It is correct that going by some of the schematics that the Rollover Switch is in line. I have no specific information for the Rollover Switch. I treat it as a black box with inputs and outputs which are complete unless the vehicle is rolled over. There is no indication I have seen which gives reason to think that it changes state otherwise.

The circuit wiring suggestion with 2 conductor cable which I show above feeds power directly to the Espar terminal. That is after the Rollover Switch.

It would be VERY COOL if I could get the setup to be choosing both REST and the aux heat together to fire up the heat as we both want. No new switches.
:idunno:

What happens if Fuse #7 were powered while the key is off?
Nothing. I have already tested that. Also no response even with REST enabled.


I also assume that the main power for the Espar comes from the Red #1 since that is a 20 amp fuse. I could feed that from the Aux battery all the time.
It is the Red #1 pin. The Booster Heater fuse is typically 25 amp.

To add more confusion to the game. I also have a 10 amp Fuse Position #7 listed on my fuse map as "Heater Booster Ter. 15". The wire coming off that fuse is BK/DG. I have not found that wire color called out in any of the MB Booster Heater documentation which I have uncovered.

To get operation similar to the Aux Heater out of the Booster Heater you also need to get fan control. The Booster Heater has no fan relay. The fan is controlled by the ATC.

Even though I admit to being in the dark about some details, the REST/Booster Pre-heat shown above will do what I say. It is a simple switch circuit. It wasn't simple to design in that it didn't just jump out at me without some investigation.

vic
 
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Than you Vic,
I think this will help many people that would like to run the booster heater with the key off.

Does anyone have a Mercedes part number for a DPDT switch that would snap nicely into the dash?

Best regards,
Nolan
 

ECU

Well-known member
No idea on switch. Looking at your diagram. Doesn't the REST button light up the pin 7 of the Espar since it is turning on the pump. This would leave only pin 6 to be powered?
I did a test when I installed the pump. One of the two became active from the REST button. I think it was #7.
Likely, this is only the case in our low end Sprinters.
I'm thinking that, in figure 2, the far right is the only wiring we have. No relay, no diode. Thus we have no splice block S362.
I can't find it in the diagrams, but logic says that the Espar would want to know that the pump is active to run in the standard engine heat mode. The rollover switches are the dash switches at the heater for controlling AC, REST and Aux heat.

My thinking is that a relay could be powered by the ignition, but use the NC connection to feed a switch to turn on pin 6. This would mean that the switch would only have power when the ignition is not on. Cranking ignition would cut the circuit. Alternately, the relay could be powered by the REST switch. This also dies when the ignition is on. But this likely would need a diode, since power might backfeed when the engine runs the aux water pump. BUT it may not, the REST circuit also runs the heater fan and it doesn't run all the time that the pump does.

Sorry if I'm typing and thinking here. Look at page 8W-42-8. The pin 3 FROM the Espar triggers a relay that triggers the fan stage low speed. This doesn't make sense. The REST works when the Espar is off (removed in my case). And this is the pin in the Espar plug not being wired at all. What else connects at S327? Tapping in to this relay could be the source for my idea. Can't use the output of the relay because then my new switch would be powered whenever the heater fan was on low. But the supply to the relay should be isolated from the aux pump power.

I've also thought about a 4000 series IC logic circuit to accomplish things. These are simple 12v AND, OR circuits. Power here, and NOT there means power out. That kind of stuff.
 

Aqua Puttana

Poly - Thread Finder
No idea on switch. Looking at your diagram. Doesn't the REST button light up the pin 7 of the Espar since it is turning on the pump. This would leave only pin 6 to be powered?
I did a test when I installed the pump. One of the two became active from the REST button. I think it was #7.
Likely, this is only the case in our low end Sprinters.
I'm thinking that, in figure 2, the far right is the only wiring we have. No relay, no diode. Thus we have no splice block S362.
I can't find it in the diagrams, but logic says that the Espar would want to know that the pump is active to run in the standard engine heat mode. The rollover switches are the dash switches at the heater for controlling AC, REST and Aux heat.

My thinking is that a relay could be powered by the ignition, but use the NC connection to feed a switch to turn on pin 6. This would mean that the switch would only have power when the ignition is not on. Cranking ignition would cut the circuit. Alternately, the relay could be powered by the REST switch. This also dies when the ignition is on. But this likely would need a diode, since power might backfeed when the engine runs the aux water pump. BUT it may not, the REST circuit also runs the heater fan and it doesn't run all the time that the pump does.

Sorry if I'm typing and thinking here. Look at page 8W-42-8. The pin 3 FROM the Espar triggers a relay that triggers the fan stage low speed. This doesn't make sense. The REST works when the Espar is off (removed in my case). And this is the pin in the Espar plug not being wired at all. What else connects at S327? Tapping in to this relay could be the source for my idea. Can't use the output of the relay because then my new switch would be powered whenever the heater fan was on low. But the supply to the relay should be isolated from the aux pump power.

I've also thought about a 4000 series IC logic circuit to accomplish things. These are simple 12v AND, OR circuits. Power here, and NOT there means power out. That kind of stuff.
:idunno:

Let me know when you figure it out. You really need to pay attention to the Program Timer, Except Program Timer, CHM, HBM, REST, etc. notes. The Booster Heater scheme in my 2004 doesn't have a fan relay or circulation pump relay. Your's doesn't have those either.

The Heater Booster Module schematic clearly shows a diode in the circuit.

10.3.3 Booster.JPG

That said, a bit of testing this morning indicates that my 2004 is not wired to the 10 amp Fuse #7 as shown. Actually I haven't found any documentation which would explain my system control tests.

The BK/DG wire on my Fuse #7 eventually powers Pin #6 on the Espar without powering up the Circulation Pump. My Espar will fire up engine/key off with the Fuse #7 BK/DG wire jumped to 12v when my REST Pre-heat switch powers Espar Pin #7. The Circulation Pump didn't run. The heater would have operated until the Espar High Temperature Safety Limit tripped it off.

My basic conclusions at this time.

First let me say that my ideas on what is really going on with my Espar Heater OEM MB modified, not original Espar Booster unit controls change as I find new information. The way they squeeze multiple control schemes into the documentation tends to make the MB schematics confusing at best.
* There probably is no diode.
* The power to Pin #6 just verifies key position and doesn't know if the Circulation Pump is running. (Both the Booster and Aux heater will operate with the engine running even with a bad pump.)

Added: It could be argued that my DPDT Pre-heat Circuit does a better job of Circulation Pump verification. I pull the Pre-heat enable power from the actual REST Circulation Pump power wire. No power to pump, Pre-heat circee no workee.

* The ATC module is likely very involved in the Booster Heater control scheme which is not insignificant.
* Some of the information is missing or even incorrect in the documentation.

You really will need to get out and do some testing because you just can't rely on the documentation. Trust me on that. It has been running me around for a while.

:cheers: vic

Thank you Vic,
I think this will help many people that would like to run the booster heater with the key off.

Does anyone have a Mercedes part number for a DPDT switch that would snap nicely into the dash?

Best regards,
Nolan
Given all the logic control and relays used by Mercedes I believe a DPDT OEM style switch will be like finding hen's teeth.

I just used a regular old bat handle toggle switch. My switch is a SPST (the old circuit with fuse and diode.) so it is likely smaller dimension than a DPDT switch will be.

RESTmodSw.jpg

vic

Added:

I was requested by PM for wire colors to the switch.

This what I came up with.

...

vic
EsparRunDPDTswitch.jpg
 
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ECU

Well-known member
:idunno:

The BK/DG wire on my Fuse #7 eventually powers Pin #6 on the Espar without powering up the Circulation Pump. My Espar will fire up engine/key off with the Fuse #7 BK/DG wire jumped to 12v when my REST Pre-heat switch powers Pin #7. The Circulation Pump didn't run. The heater would have operated until the Espar High Limit tripped it off.

vic
Odd. The REST should fire the pump and fan. That is what it is all about.
 

Aqua Puttana

Poly - Thread Finder
Odd. The REST should fire the pump and fan. That is what it is all about.
I didn't enable REST for that test.

:idunno:

The BK/DG wire on my Fuse #7 eventually powers Pin #6 on the Espar without powering up the Circulation Pump. My Espar will fire up engine/key off with the Fuse #7 BK/DG wire jumped to 12v when my REST Pre-heat switch powers Pin #7. The Circulation Pump didn't run. The heater would have operated until the Espar High Limit tripped it off.

vic
I jumpered 12v to the load side of the Fuse #7 BK/DG wire. (Fuse was removed.)

I switched on my added early design diode/REST Pre-heat dash switch to power Pin #7 BL wire from the battery.

I didn't touch the REST switch.

The heater fired up.

The Circulation Pump did not run. (Per the schematics, powering the load side of Fuse #7 should power the pump. It doesn't on mine.)

No circulation so I powered off the heater to avoid damage.

********************

Espar Pin #6 and #7 are the enable inputs on the Mercedes bastardized modified Espar units.

Per my test, my Fuse #7 Booster Heater Ter 15 (BK/DG) is not wired as is shown in any of the schematics. If it was wired like they indicate then the Circulation Pump would have run when I jumpered 12v to the load side of the fuse holder with the fuse removed.

vic
 
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davisdave

2005 140 tall passenger
REST/Booster Engine Pre-heat with DPDT Switch Modification
My test light shows that the pump runs 100% of the time.
vic
This is interesting...explains why everybody has replaced this pump at least once. I was wondering how my pump could wear out since i never use the REST! Makes a separate switch for the pump a little more attractive:thinking:
switch panel.JPG
 

Aqua Puttana

Poly - Thread Finder
... Makes a separate switch for the pump a little more attractive:thinking:
View attachment 64529
Except that for the OM647 engine the pump circulates through an oil cooler and the EGR as part of the path. It may be best to keep it OEM. :idunno:

vic
 
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ECU

Well-known member
I did some testing, too rainy to stand out there much. But the Fuse #7 (which is fuse #13 on mine) does send power to pin 6. Don't know if it is direct or through other electronics. I didn't have my ohm meter.
I jumped it to +12v and ran the REST. Both pins showed to be hot. But the heater did not fire up. Could have been the truck or atmosphere too hot to run. Couldn't tell today.
 

Aqua Puttana

Poly - Thread Finder
... But the Fuse #7 (which is fuse #13 on mine) does send power to pin 6.
The fuse positions do vary from Sprinter to Sprinter. It happens that my Fuse #7 position agrees with some schematics, but I think that is dumb luck. I have yet to find any logic as to what/where Fuse Block #3 is. For some reason FB #3 does seem to often come up in the CHM and HBM documentation.

Don't know if it is direct or through other electronics. I didn't have my ohm meter.
I don't know either. The documentation I have hasn't been specific or very helpful.

I jumped it to +12v and ran the REST. Both pins showed to be hot. But the heater did not fire up. Could have been the truck or atmosphere too hot to run. Couldn't tell today.
The ambient temperature lockout is on Sprinters from 2010 up. Our T1N's do not have that wonderfully important save the planet mandated feature.

My latest thinking would be that it doesn't run because the logic of the ATC module isn't satisfied. My recent explorations are based upon the ATC module being the brains behind the Booster Heater operation. The Espar control module just controls the diesel firing. (It is capable of much more control with an original Espar control scheme.) I'm quite certain that with a Heater Booster Module HBM option the ATC module exclusively controls the Circulation Pump, the REST Fan Stage #1 speed operation, and other needed auxiliaries. A missing power input to the ATC module logic could possibly be keeping you locked out.

If it continues to keep my interest I'm pretty certain that I can track down the actual circuit operations. The variations in the documentation make it frustrating enough that I may just walk away. I know enough to get the heater to operate as I want. I'm not interested in using it for an RV heater. If I'm stuck for some reason I can just keep hitting the REST button for another 30 minutes of heat... until my starting battery dies. :rolleyes:

vic
 
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Hello Vic,
If you had a second battery with an isolator could you run the heater and pump from that so it wouldn't drain the main battery?

Best regards,
Nolan
 

Aqua Puttana

Poly - Thread Finder
Hello Vic,
If you had a second battery with an isolator could you run the heater and pump from that so it wouldn't drain the main battery?

Best regards,
Nolan
It can be done. The question is whether it is worth the effort and cost. It would be a bit complex to change over an MB OEM Espar Heater Booster Module HBM to use other than the starting battery power, and more importantly, integrating the needed the ATC module controls into the scheme.

Not that you asked.

Many things can be done to modify different equipment DIY at fairly low cost. The DIY project has the advantages of interesting exploration, testing different methods, trying another method if one doesn't work, and time invested not being so much of a constraint among other things.

In my opinion, even paying someone to install the circuit as outlined above for Booster Pre-heat probably makes sense. The convenience and benefits of engine pre-heating does have real value in cold climates. To pay to have someone do more modification not so much.

If your needs are really to have a reliable cabin heater module to run off a house battery then the only real answer in my mind is to install a D2 Airtronic or other stand alone heater. It will cost a few dollars, but there will be no dependence upon the more complex MB controls for that stand alone heater. Heating the air directly and dumping the heat where you need it is better than always heating extra mass. To make it worse, the OEM system heated air that you do get is dumped into the front area that you don't normally occupy. That extra mass is the engine and related parts sitting in cold ambient temperature by the way.

:2cents: vic
 
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ECU

Well-known member
From reading on the site here and the schematics. I think that the Espar could be fed aux battery at the fuse block where it feeds Pin 1. The hard part is the fan. That stuff, plus the radio and other aux equipment can be fed at Fuse #8 in the fuse box under the steering
An alternate and easier trick is to use the main battery and hold the aux in reserve. Using the aux battery relay/isolater to connect them together for jumping. That, I already have installed.
 

vanski

'05 Snow Camper, '17 170 4x4, Adventure Vissionary
Vic, ECU:

Once again, great stuff here and very much related to a ton of effort I'm putting in and about to put additional time into; rebuilding my Espar over the weekend.

Question: Doesn't the below post from 'General Espar Heater Wiring Information' which referenced a post from 'Wiring Heater Booster to run from Switch' satisfy running the Espar while engine is off and providing power to the coolant pump?:

Originally Posted by jimwhs View Post
After reading and searching around the forum last year, I found that back in 2011, a guy (user name prsiii) posted what I thought was a elegant solution. And it works great. The wiring was rather simple, and as he said, is done entirely inside the cab, no adding wires between the cab and the engine compartment. I don't understand why no one else ever really picked up on it. Here is what he described, with a few little additions provided by me to clarify some details. Note however that I added just 1 simple switch to turn on the Espar along with the pump. It took me a few hours to do this to my 2005 2500, and then I added a small additional heat exchanger and fans near the back of the van to heat the "living space"

Posted by prsiii, on 6/17/2011
Bent on installing a 7-day and a home made 'controller', today was an 'interesting' afternoon...in the fortune cookie sense. My first discovery was not only are the fuse locations in the service manual 'wishful thinking' but the MB schematics are not at all accurate as they relate to an MB chassis for a Winnebago Class C. I do have this to say after getting everything working like a champ: The
'controller' circuits published previously are gross overkill to accomplish the job: I did my mod with only one relay, a couple of 3amp diodes, and NO wires going through the firewall to the heater.

Current measurements for the record books from my rig:
Timer idle and heater bias (timer backlight is off) = 55mA
Water pump, system hot = 650mA
Fan on low = 4.6A (had to test this by pulling the 30A fan fuse, I won't be using that dash fan for sure! My new exchanger draws 1.2A on high)
Have not taken current readings on the heater, assuming 60W/5A on high per the manual.

Noteworthy: The most annoying and difficult aspect of the published control shows a pair of wires going to the Espar. The odd thing is what this wire does: In the manual, it is called 'Terminal 15' and in another place it is called 'D+', what it really is connected to is the D+ (engine is running) bus. That's right, it tells the heater when the keys are in the ignition and the engine is running. This is what prevents the heater from running by itself. [If "inhibit" is intended then the blue statement is incorrect. There is simply no power for the Espar Pin #7 (enable or run) from the D+ until the key is on.] In the service manual, this signal is run through Fuse Block 3 #7 (10amp.) ky sprinter has no Fuse Block 3, but on the chart behind the panel there is a 'Boost Heater Terminal 15' fuse in Block 2 #6 (10amp.)

This is what you do:
1) Go to the auto parts store and get one of those ATC fuse holders with pigtail wires, and two splice in terminal blocks.
2) Remove the drivers seat (4 allen key bolts) and locate the 'Boost Heater Main Fuse' (25amp.)
3) Remove both boost heater fuses.
4) Behind the fuse block, locate the small-ish wires coming from both fuses, usually they are going into the lower terminal (closest to the road.)
5) Splice the new fuse holder to the wires coming from both fuses
6) Install the 10amp fuse into the new fuse holder
7) Re-install the 25amp fuse
...now the heater will think it's okay to run when commanded, as 12v is on both the power and 'Terminal 15.' Note there is no messing
under the hood, running wires, etc. Simple, eh?

To make the heater and water pump run, now all you need is to inject 12V into the appropriate wires in the ATC (this time ATC stands for the dash climate control unit) harness: Green/Red wire (fires up the pump) and Blue wire (fires up the heater.) The pump should run from a relay because it draws about an amp at startup, but drops to 600-700ma during normal operation. The blue wire is a logic signal, it will operate with only 15mA of current. I drove the blue wire from a diode from the same signal that drives the relay. That way the signals are independent when all is off. The dash blower will only be run by the REST function (30min max) to ensure I never drain the battery. My secondary heat exchanger will run off the coach batteries.

For me, I wired the 7day timer so that both +12 and ACC go to the battery (disables the 2hr runtime limit) and that kicks the blue wire and the relay to run the water pump. Next project is the plumbing to the coach heat exchanger, and I hate plumbing;)

And point of clarification of exactly what I did in the dash, I took power from the cigarette lighter to my new switch, connecting the switched 12v to 2 2A diodes that connected directly to the Green/Red and to the Blue wires on the ATC. I didn't see the need to add a relay for a signal that has a peak current draw of 1 amp.

This is the route I've been planning on taking but it seems like others have taken much less straight forward approaches for some reason.

As usual, greatly appreciated! :bow:

Chris
 

ECU

Well-known member
For me, I think that would work. I'm leaning that direction. But digging under the dash could take more effort than wiring at the heater. We've found that our wiring things are different than the other guys too. Plus I'm slow at things. I've been working on my van for five years now. Still not finished.
 

Aqua Puttana

Poly - Thread Finder
Vic, ECU:

Once again, great stuff here and very much related to a ton of effort I'm putting in and about to put additional time into; rebuilding my Espar over the weekend.

Question: Doesn't the below post from 'General Espar Heater Wiring Information' which referenced a post from 'Wiring Heater Booster to run from Switch' satisfy running the Espar while engine is off and providing power to the coolant pump?:

Originally Posted by jimwhs View Post
After reading and searching around the forum last year, I found that back in 2011, a guy (user name prsiii) posted what I thought was a elegant solution. And it works great. The wiring was rather simple, and as he said, is done entirely inside the cab, no adding wires between the cab and the engine compartment. I don't understand why no one else ever really picked up on it. Here is what he described, with a few little additions provided by me to clarify some details. Note however that I added just 1 simple switch to turn on the Espar along with the pump. It took me a few hours to do this to my 2005 2500, and then I added a small additional heat exchanger and fans near the back of the van to heat the "living space"

Posted by prsiii, on 6/17/2011
Bent on installing a 7-day and a home made 'controller', today was an 'interesting' afternoon...in the fortune cookie sense. My first discovery was not only are the fuse locations in the service manual 'wishful thinking' but the MB schematics are not at all accurate as they relate to an MB chassis for a Winnebago Class C. I do have this to say after getting everything working like a champ: The
'controller' circuits published previously are gross overkill to accomplish the job: I did my mod with only one relay, a couple of 3amp diodes, and NO wires going through the firewall to the heater.

Current measurements for the record books from my rig:
Timer idle and heater bias (timer backlight is off) = 55mA
Water pump, system hot = 650mA
Fan on low = 4.6A (had to test this by pulling the 30A fan fuse, I won't be using that dash fan for sure! My new exchanger draws 1.2A on high)
Have not taken current readings on the heater, assuming 60W/5A on high per the manual.

Noteworthy: The most annoying and difficult aspect of the published control shows a pair of wires going to the Espar. The odd thing is what this wire does: In the manual, it is called 'Terminal 15' and in another place it is called 'D+', what it really is connected to is the D+ (engine is running) bus. That's right, it tells the heater when the keys are in the ignition and the engine is running. This is what prevents the heater from running by itself. [If "inhibit" is intended then the blue statement is incorrect. There is simply no power for the Espar Pin #7 (enable or run) from the D+ until the key is on.] In the service manual, this signal is run through Fuse Block 3 #7 (10amp.) ky sprinter has no Fuse Block 3, but on the chart behind the panel there is a 'Boost Heater Terminal 15' fuse in Block 2 #6 (10amp.)

This is what you do:
1) Go to the auto parts store and get one of those ATC fuse holders with pigtail wires, and two splice in terminal blocks.
2) Remove the drivers seat (4 allen key bolts) and locate the 'Boost Heater Main Fuse' (25amp.)
3) Remove both boost heater fuses.
4) Behind the fuse block, locate the small-ish wires coming from both fuses, usually they are going into the lower terminal (closest to the road.)
5) Splice the new fuse holder to the wires coming from both fuses
6) Install the 10amp fuse into the new fuse holder
7) Re-install the 25amp fuse
...now the heater will think it's okay to run when commanded, as 12v is on both the power and 'Terminal 15.' Note there is no messing
under the hood, running wires, etc. Simple, eh?

To make the heater and water pump run, now all you need is to inject 12V into the appropriate wires in the ATC (this time ATC stands for the dash climate control unit) harness: Green/Red wire (fires up the pump) and Blue wire (fires up the heater.) The pump should run from a relay because it draws about an amp at startup, but drops to 600-700ma during normal operation. The blue wire is a logic signal, it will operate with only 15mA of current. I drove the blue wire from a diode from the same signal that drives the relay. That way the signals are independent when all is off. The dash blower will only be run by the REST function (30min max) to ensure I never drain the battery. My secondary heat exchanger will run off the coach batteries.

For me, I wired the 7day timer so that both +12 and ACC go to the battery (disables the 2hr runtime limit) and that kicks the blue wire and the relay to run the water pump. Next project is the plumbing to the coach heat exchanger, and I hate plumbing;)

And point of clarification of exactly what I did in the dash, I took power from the cigarette lighter to my new switch, connecting the switched 12v to 2 2A diodes that connected directly to the Green/Red and to the Blue wires on the ATC. I didn't see the need to add a relay for a signal that has a peak current draw of 1 amp.

This is the route I've been planning on taking but it seems like others have taken much less straight forward approaches for some reason.

As usual, greatly appreciated! :bow:

Chris
I have my problems figuring the MB heater controls even with documentation. I do agree with the comment that the MB schematics aren't always accurate.

Without at least some basic documentation showing his modifications I really can't comment on everything which was presented above. Discussion of circuits using just wire colors can be misleading. I have found that the MB wire colors change depending upon specific heater types ordered from the factory.

It worked for him so it should be worth copying.

vic

P.S. - Getting a 2 conductor cable from under the dash out to the Espar heater is not a big deal. I used a spare chunk of trailer harness wiring. Getting wires from under the driver seat to the dash seems a bit more complex to me.
 
Last edited:

ECU

Well-known member
Overthinking. With the way the guy set it up, the REST would control the pump, so he only needs to feed power to the blue wire. But this needs to be controlled by the REST so it will shut off on it's own. So you could pull power FROM the Green/Red to feed the blue.
 

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