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Old 01-25-2010, 12:31 PM   #62
Aqua Puttana
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Default Re: Stoopid things I shoulds known!!

Auxiliary, Boost Heater and REST Description of Operation

Search: Auxiliary Auxilliary Aux Booster Espar Heater REST function operation

As I was originally confused about the Booster Heater, Auxiliary Heater, and REST functions. I'll outline what I THINK I know for those who may not be up to speed. Edit: What I include here is basically correct. There is a fixed time heater switch option left out along with some other small exclusions in my notes. I'm too lazy to edit/correct this entire first post.


The circulation pump on my 2004 is mounted on the firewall to the left of the battery above the EGR. One hose goes to the EGR valve. The other from the Booster Heater via a steel coolant line. The direction of coolant flow is from the EGR to the Espar heater. I'm certain that varies with year or if you don't have a booster heater (Edit: REALLY???.... should be and when you don't have a booster heater).

With my 2004 the coolant circulation pump runs for 2 seconds or so after the engine is turned off. Mine has a bit of a noticeable hum. It seems normal as there has been no problems other than the brushes wearing out.

Often the pump motor brushes can be replaced DIY to avoid the purchase of a $100.00+ pump assembly. Links:

Apparently there is also a VW -Bosch(?)- branded circulation pump that is identical except for the electrical connector for a bit less cost.

The REST function is a timed operation of the electric circulation pump which scavenges heat from the engine by running the circulation pump and the cabin fan after the engine is shut down. On mine the blower fan runs at low speed with REST on. The rest function and LED cycle off if the engine is running. Per MB you can extract heat for about 30 minutes. The REST function does not operate the Booster Heater (unless modified).

The Booster Heater function is a diesel fired heater located below the battery in the T1N Sprinters. It is most easily accessed by removing the grill and headlight pod. The Booster Heater operates with the engine running to add heat to the heater core for the cabin heater. The OEM Booster Heater will not operate with the engine off unless the controls are modified for constant operation. The engine coolant pump will circulate coolant through the booster heater at low vehicle speed and engine RPM. The electric circulating pump on the firewall is not needed for the Booster Heater to operate when the engine is running under specific operating conditions (coolant temp, vehicle speed, +).

Edit: The Booster Heater can be wired to run with the engine off.

REST/Booster Engine Pre-heat with DPDT Switch Modification

The OEM Auxiliary Heater is mounted in the same location as the Booster Heater in the T1N Sprinters. The Auxiliary Heater has an OEM digital control panel which allow the Auxiliary Heater to be operated when the engine is not running. It includes additional timers and controls not included with the OEM Booster Heater. The Aux Heater can be used to pre-warm the engine before starting. It will also perform the same as a Booster Heater with the engine running.
Added: There is another less common OEM Auxiliary Heater version which has a simple dash switch for control/operation.

Some 2004 Espar Heater Notes


2010/12/06 edit: A more formal description. Thanks goes to bc339 Bruce.
Originally Posted by bc339 View Post
To add to Vic's explanation, trying to prevent further confusion, I copied this description in the service manual for the supplemental heater:

Vehicles equipped with the optional diesel engine are also equipped with a supplemental heater unit. This unit is mounted under the vehicle and operates similar to an oil fired furnace. The heater burns small amounts of fuel to provide additional heat to the coolant. Coolant is routed from the engine, to the supplemental heater, and then to the front heater core. This provides additional heat to the passenger compartment. The system is interfaced to the vehicles on-board computer systems and DRBIIIt diagnostics. The supplemental heater unit has an electronic control module that monitors the heat output of the heater. The heater operates at full load (5 kW), half load or idle mode (no additional heat) depending on coolant temperature.
The supplemental heater is activated via the temperature control on the heater-A/C control. The heater is activated when the temperature control is set to/or above the upper set point. The supplemental heater can operate in a full or partial load range as well as an idle mode, all dependent on the engine coolant temperature. The heater unit will also turn off if the temperature control is set to less than the lower set point. The supplemental heater can take up to three minutes to completely shut down when either the heater temperature is set below the lower set point or the vehicle ignition is turned off. The supplemental heater only operates when the engine is running, the mileage exceeds 8 kilometer (5 mph) and the fuel tank volume exceeds 1/8 of a tank. The heater should start if the coolant temperature is below 40 C
(104 F).

When I was troubleshooting my coolant pump failure last year, this explanation helped me figure out why my Heater Booster would work, but not the Aux Heater.
My Sprinter is configured with the supplemental heater located behind the left headlight - controlled by the Heater Booster Switch (below the A/C switch), REST feature and the Auxiliary Heater, controlled by the 7 day timer.
The Heater Booster and Auxiliary Heater use the same heater unit, but are not controlled or operate the same. The REST feature is totally separate.

2010/05/09 edit:
Both the REST and Booster Heater are controlled by pressing the round knob like segments on the right of the dash in NAFTA Sprinters. With the engine running, the Booster Heater is operated by pressing the Bacon Bowtie switch. An LED will light for the function that is enabled.

2010/02/07 edit:
A recent thread about the booster heater. "Works while idling in 'Park' on my 2006 2500. Booster fires up almost immediately after starting the engine." Matt/Smoky pond
Additional info from Bill Drescher "houndsofheaven" on Sprintervan:
correct - my diagnosis of an inop coolant pump was made because the Esapar worked fine with the engine running [Add - The main belt driven coolant pump was operating. - vic], but shut off quickly when the engine was not running (Auxiliary Heater)

Another comment added by Bill:
and can be used to keep the engine/cab warm when you go into a store. It is one of life's great pleasures !
Some additional comments 2010/08/16. Thanks goes to Douglas.
Originally Posted by Douglas Hicks View Post
Some heaters come with a duct for hot/warm air. I have a dsl fired auxilary heater for my 2005. It is an option I sspecial ordered. It is mounted behind the left headlite. My heater control is in the lower center of the dash panel. I push the button with the red squiggly lines, holding it down until I hear the to dosing pump click. Dosing is a fancy, expensive way to say fuel pump. If the driver's door is open, you can hear the aux heater come on, it sounds like a jet engine. The exhaust pipe exits by the left front wheel. The heater heats the engine coolant, which is circulated by a 12V pump. There is a thermostat someplace. If you have a diesel fired heater, no matter the location, run it for 10 minutes a month. The DAD is thought to diagnose heater problems.

Some heaters are mounted in the cargo/passenger area. In my 2003, we added a heater there. It is diesel fired, thermostatically controlled and forces hot air into the rear compartment. Some vans may have had that heater installed at the factory.

There is also another heater, the REST. It uses [scavenges] residual heat from the engine to keep the cab warm. Push the lower button to operate the REST when leaving the van for a few minutes. It will run w/o the key, for about 20 minutes, at least in my van.

Heaters are another mystery in our vans. No one, except Dr A understands all of the options in the Sprinter. There are rumors MB calls him for help.
20100918 edit - A recent thread which includes pictures of the various control panels for heaters. Rick found someone had replaced his Aux Heater control panel with an incorrect unit that didn't have the wavy lines. Thanks goes to Rock Auto and Ricksan.

Note: This is an unusual situation. A booster heater (basically runs when the engine is running) can be changed to an aux heater (will run as set by the controls), but it is not as easy as just changing the control panel over. A search will provide more information on the steps necessary.

New owner 2005 3500 158

2010/10/24 edit: A recent thread over at Yahoo sprintervan which has some good information from members.

2010/12/28 edit:
That list of options left out the T1N's rear cabin heat exchanger option: H13.

More info about the rear heater thanks to autostaretx (Dick) is in this post.

2010/11/04 edit: A thread about the NCV3 heaters complete with pics of the controls. Thanks goes to all contributors.

NCV3 Heater Systems

REST/Booster Engine Pre-heat with DPDT Switch Modification

A recent discussion regarding the different OEM MB control schemes for the Espar heater.
I think I found a heater booster, but no switch

Please feel free to correct any errors or add information. I hope this does some good. AP/vic

Program Timer

I found this guy's comments helped me to easily operate and program my 2006 Espar timer.

DAD NAS (N. Amer. Spec) 2004 140 2500 >330,000+ mi. Arctic Whitewash Brush-tone Grey
2006 Freightliner 140 2500HC >183,000+ mi. Arctic Whitewash (Spotted Snow Leopard accents)
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Last edited by Aqua Puttana; 02-12-2018 at 01:23 PM.
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