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Old 02-12-2018, 12:49 PM   #1
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Default Booster Heater


I have a 2004 Westfalia, Im in Sweden so itīs called a James Cook. I have a question about the Booster heater thats located under the hood, below the left headlight:
Am I supposed to be able to pre heat the van with this without turning the engine on?
In the regular sprinters I think this is just a booster that kicks in when neccessary when the engine is running. But I cant seem to find an answer to whether the Booster Heater is connected to the camper control panel in the roof? Does anyone know? Is there a way to program it, or start it with the control panel?
Also, I think the booster heater is faulty, I have never seen any smoke coming from the exhaust under the wheel well.


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Old 02-12-2018, 02:19 PM   #2
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Default Re: Booster Heater

First let me extend to you a hale and hearty welcome to the forum. welcome2.gif

I have no idea as to James Cook modifications.

There are a few different OEM heater modes for the T1N. I attempt to explain some of the OEM T1N heat options here.


If you have the REST option a Booster Heater can be fairly easily modified to give approx 30 minutes of engine pre-heat. I find that time adequate down to about -15F (the lowest ambient I see).

REST/Booster Engine Pre-heat with DPDT Switch Modification

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Old 02-12-2018, 07:35 PM   #3
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Default Re: Booster Heater

Welcome to this subforum and please post follow-up as to whether you have the same or different set-up. Thanks.

1. Differences

NAFTA (North American Free Trade Agreement) Westfalias are built on 2004 Dodge Sprinters (rebadged and modified for US market Mercedes Sprinters) with Westfalia James Cook conversion with NAFTA modifications and Airstream added upgrades.

There will be differences between our Westies and your James Cook.


Besides this wonderful subforum, there is also the Yahoo Sprinter Westfalia Group and the James Cook Friends Forum (German with English and other language translations).

Also, another source for manuals and other info is:


The repair manual is extremely useful, and is at the above website in pdf format.

3. We have the hydronic coolant heater under the left driver side headlight (Sprinter controlled) and the Airtronic Espar heater next to diesel/gas tank (Westfalia controlled).

The hydronic heater is NOT controlled by the Westfalia central computer console at the top of the windshield. Instead, it is controlled by two (2) switches:

A. Rocker Switch with 3 vertical wavy lines near the transmission shifter (where the heated seat switches are, if any, and other rocker switches like central locking).

In the Dodge Sprinter Owner's Manual, chapter on "Understanding Your Instrument Panel," Auxiliary Heater Switch:

Press top of rocker switch, and heater operates for 120 minutes and then turns off by itself. A little light on the rocker switch lights up when on.

Press bottom part of switch to turn off.

This switch works whether engine is on or not. So can use when engine is off or when engine is running.

Also, when engine is off, the ignition can also be off.

The heater operates off the engine battery.

A copy of the Dodge Sprinter Owners Manual is at the SprinterWestfalia.com website posted above.

B. Heater Booster Switch

Only when engine is running. Helps.to heat up engine to operating temperature and to get heat to cab area.

The button is the middle horizontal bar of the far right circular control (top part is air conditioner with snowflake symbol, middle part is heater booster with vertical wavy lines, and bottom half is REST)

C. Other Options

There are other options which can be added.

For example, there is apparently a 7 day timer control available, which replaces the rectangular coin receptacle in the transmission shifter area.

Also, poster PNWSquid added a remote control to his hydronic heater:



Last edited by OldWest; 02-12-2018 at 07:54 PM.
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Old 02-12-2018, 07:43 PM   #4
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Default Re: Booster Heater

The hydronic heater does NOT operate unless you turned on one of the two switches mentioned above. So check to see if it works.

(I don't know what happens if both switches are turned on.)

If it does work but only for a few minutes it may be because coolant is not circulating and the heater turns off automatically.. On the firewall under the brake master cylinder, there is a hand-sized cylinder which is a Bosch Auxillary Pump. The lifespan of the pump is about 70-80 thousand miles. If the pump dies, the hydronic heater won't work.

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Old 02-13-2018, 05:45 PM   #5
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Default Re: Booster Heater

Regarding that pump, I replaced mine recently. It was a relatively easy job. You can find instructions somewhere on the forum. Trying not to drop screws was the hardest part.

Apparently this pump does in fact run at certain times even when the Espar booster heater is not running. So it is a good idea to replace it if it is dead even if you don't use the booster much. This is why the pump seems to wear out regardless of the amount of actual use of the booster.

Question about the two different switches that I've always wondered: When the engine is running, is there any difference between using the special rocker switch vs. the button that is integrated into the climate control area to turn on the booster heater?
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Old 02-13-2018, 07:37 PM   #6
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Default Re: Booster Heater

Yes, timing--how long heater operates.

Believe the following from reading but have not personally verified.

1. Rocker Switch

Basically a timer for 120 minutes, whether engine is running or not.

So it's a fixed timer with a manual off.

So if you run engine for a short errand of 20 minutes, the heater continues to operate while you're shopping, etc., until you turn heater off.

Presumably, heater shuts on/off if heater gets too hot (coolant reaches a certain temp) but fan continues to blow heat.

If drive for five hours, heater turns off after 120 minutes. So if in Siberia, may want to use the horizontal Heater Booster switch (in the circular AC/REST control).

2. Heater Booster Horizontal Switch (AC/REST Circular Control)

No timer so operates as long as engine is running and switch is on.

Not required for temps above 41F.

When switched on (when engine is running), the heater will turn on if coolant is below 167F and off when coolant reaches 185F, and on and off as coolant temp changes.

No time limit so if drive more than 120 minutes and want heater to be on, use this switch (unless, instead, you want to use rocker switch and turn rocker switch off and on every 120 minutes).

If turn engine off WITHOUT turning switch off, the switch has a memory function so heater is turned on when engine is started again

NOTE: When turn engine off, the heater may continue to run for 2 minutes in cooldown.

NOTE: Supposed to operate heater once a month for at least 10 minutes.

NOTE: If fuel is too low (4 gallons remaining), heater will not operate.
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Old 02-13-2018, 07:48 PM   #7
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Default Re: Booster Heater

When my Bosch auxillary pump went out, it made a noise like the engine was continuing to run after turning the ignition off. Very noisy.

I thought the Westy also ran a little hotter on the freeway when pump was apparently dying.

Dr. A replaced. He also showed me a quick test to see if pump was dead. I don't remember the test but I think I posted the info several years ago (could be in the Yahoo Sprinter Westfalia group).

If someone knows, please post.

The replacement cost of the BOSCH pump has also fluctuated quite a bit during the last decade. Anything at or below $100 is probably a good value (Europarts-SD.com).

For handy folks, the pump can probably be rebuilt. Apparently, the motor brushes wear out. Search the other subforums.


Last edited by OldWest; 02-13-2018 at 08:13 PM. Reason: Add link re pump.
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Old 02-13-2018, 08:00 PM   #8
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Default Re: Booster Heater


The Westy may have been rewired to operate like you indicate as we have the rocker switch. I avoid cold areas so primarily use the rocker switch for ease of use.

A couple of times, I've driven in colder areas and tried the horizontal switch (AC/REST) but never compared if engine got warmer faster and never.got out of Westy to see if heater was actually working.

If kept more like other Sprinters, then the bottom 1/3 half circle is the REST and turns on the coolant pump for residual heat. (Good you mentioned tue residual heat turning on coolant pump--This may be part of Dr. A's quick test but I don't remember.)

Then the horizontal 1/3 middle button would turn the heater on/off when engine is running, UNLESS Westfalia completely superseded with the rocker switch.

Quick way to check is to start engine and push the horizontal switch, and then go outside and see if the heater turned on (assuming everything is working properly).
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Old 02-13-2018, 08:21 PM   #9
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Default Re: Booster Heater

Thanks for all the replies!
I dont have the rocker switch on the console, but I do have the horisontal switch, and also theres a timer function on the control panel above the windshield. The symbol is a clock. My instruction manual is in German and my German is bad these days, but I think it says I should be able to program the heater to start. I also have the airtronic d4 which is controlled by the panel and only heats up the interior of the van.

Im unsure whether the booster heater under the hood is working. When I turn the engine on and press the horisontal switch with the wavy lines, the hose at the top of the heater gets somewhat warm, but I cant see any smoke coming from the exhaust. The light on the switch lights up. When I turn the engine off everything gets quiet right away, no sound of a fan or heater winding down. But engine temp rises quite fast and the van stays warm although its cold outside.
Does a functioning booster heater make noise and smoke, is there a sure way to make sure it works?
Again, thanks for the replies and the hearty welcome!
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Old 02-13-2018, 09:18 PM   #10
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Default Re: Booster Heater

1. The clock/timer on the central computer console above the windshield is for the Airtonic D4S (NOT the hydronic heater). (Unless, of course, yours is different than ours.)

Download the Westfalia Motorhome Supplement Manual from the SprinteWestfalia.com website to figure out how to set the clock and up to three (3) starting times for the Airtonic to start and run for 2 hours each time.

To turn on each starting time, you press the clock once and the power button, again the clock with the power button, and then again the clock with power button for third starting time (or whatever of the three starting times you want).

Difficult to explain but manual is fairly detailed.

As your English is perfect, the manuals in English may be easier to figure out than your German manuals. Of course, there are differences between our Westy and the James Cook, but a lot of info should.be the same.

2. Hydronic Heater

The exhaust could be clear and not smoky. You might try feeling for any exhaust air from the hydronic heater--be very careful as could be very HOT. Better idea: use an infrared thermometer pointed at the exhaust pipe.

Insofar as the 2 minute cooldown period when engine is turned off, it may be that heater has already turned off while engine was running (so cooldown period occurred while engine was running).

The Sprinter engine is so noisy it'd probably be hard to hear the hydronic heater with the engine running.

Too bad you don't have the rocker switch. Try posting on the James Cook Friends Forum to find out if your James Cook is unique or not (maybe rocker switch was an option).


Last edited by OldWest; 02-13-2018 at 09:21 PM. Reason: Clarify above the windshield.
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