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Old 01-04-2014, 03:56 PM   #1
Aqua Puttana
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Default T1N Booster Heater Wireless Control

T1N Espar Booster Heater Wireless Remote Start/Run

The following circuits should allow the T1N Sprinter Booster Heater to run in "Engine Off" Mode using a local manual select switch or a remote control wireless unit. I have not tested or verified the remote circuit operation (the "Local" circuit is tested and works), nor do I intend to. I'm just trying to help out based upon posts requesting wireless remote control for engine pre-heating

My basic design concepts include isolation of all added 12V control so that it would not backfeed into the ATC or any other Sprinter OEM controls. The control wires that are needed to tap/intercept *should* all be available in the dash on the ATC with the exception of the diode feed under the hood. (I find the ATC/Cabin Heater Control detail less than ideal, so FWIW.) To help to avoid battery drain the circuit only powers the aftermarket base remote unit while the system awaits Fob activation in "Remote Select". It also does not impress any voltage on the Espar unit until the system is enabled with the wireless remote contact.

I believe that the system can be added for under 50 bucks in parts. Costs go up depending upon the parts selection/acquisition, especially the aftermarket remote unit selected.

Note: These circuits do not include any of the OEM Sprinter time outs, fuel level, or other controls. It is intended only to run the Espar Heater without the engine running for pre-warming the engine/cabin.

While in "Local Select" mode the Booster Heater run time is subject to the REST System approx 30 minutes via the diode. When enabled in "Remote Select" mode there is no time out. Once enabled the Espar Booster Heater will essentially run forever. (It is *possible* that MB had Espar include a timeout in the Espar combustion control module. I have no details on what MB required for the custom control module.) You have now been informed/warned.

Basic Circuit Operation While in "Local Select" Mode

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Basic Circuit Description

The SPDT switch opens the blue wire from the ATC Automatic Temperature Control to stop any feedback of 12V to the ATC or other circuits. The constant 12V(+) (eg. - from the Power Outlet) feeds through the SPDT switch via the OEM blue wire to power Pin #7 "Heater On" or enable on the Espar heater. Note: The Espar will not actually start until it gets the "Pump Power Verify" signal to Pin #6 from the REST operation. With the added "Remote" cicuit the polarity blocking diode near the "Wireless Base" in the diagram prevents the 87aF and 87aP relays from energizing while in "Local" mode.

When the REST button is pushed the Aux Electric Coolant Pump is energized for a time of approx 30 minutes. The wire tapped off the DG/RD wire at the pump connector feeds 12V "Pump Power Verify" or 2nd Enable via the diode to Pin #6 of the Espar Heater. When the REST fan times out the "Pump Power Verify" 12V goes away and the Espar heater initiates a shutdown. When Pin #6 of the Espar is energized during any normal OEM Sprinter operation then the diode blocks any voltage from backfeeding to the Coolant Pump. (A diode in this configuration acts like a check valve in a water system.)

This circuit will not adversly affect any other OEM Sprinter circuit operations. The REST System will not turn on the Espar heater until the SPDT switch is "On" to enable Pin #7.

Using the SPDT switch assures no backfeed of power to the ATC or any other circuits. I wasn't able to determine for certain whether backfeeding of voltage to the ATC would have any adverse affects or not. The safe route is to use the SPDT switch.

It *may* be OK to just use a SPST switch and feed the Blue Pin #7 wire 12 volts directly without worrying about feedback. I don't recommend doing that though.

Basic Circuit Operation While in "Remote Select"

The "Local/Remote" SPDT switch is placed to "Remote". The "Engine Off Heater Mode" SPDT switch is then placed to "Enable" or "On".

At this stage that only energizes the aftermarket wireless remote base unit. The circuit is then ready/waiting for the wireless remote Fob activation.

When the wireless remote contact is latched closed 12V power is applied to the Espar Pin #7 enable via the SPDT switch and OEM Blue wire.

At the same time both the 87aF and 87aP relays are energized. That provides 12V power to the OEM Sprinter Low Speed Fan Stage 1 Relay (Cabin Fan) and to the OEM Sprinter Circulation Pump Relay (Aux Electric Coolant Pump). Once the Espar Pin #6 Pump Running Power Verify is established via the diode circuit then the Espar heater will fire up.

The Espar heater will run controlled by the coolant temperature only until either of the SPDT switches is operated, or the aftermarket wireless remote contact is opened.


Basic Parts List

2 ea - SPDT switch
1 ea - Aftermarket Wireless Remote

Possible Remote Unit = RM01 1 Channel Wireless Control On/Off


2 ea - 87a Relay with scocket


2 ea - 3 Amp Polarity Blocking Diode

Possible Diode - 3-Amp Barrel Diodes
Model: 1N5404 Catalog #: 276-1144

Fuse holder(s) for diode and 12V supply (optional as circuit is protected by OEM fuses, but a bit higher amp than needed.)

Fuse(s). (5 amp = common ATC style rating for diode circuit. Maybe higher for Local/Remote SPDT switch feed - optional)

Quick taps (2 ea. under hood + ??)

Misc. Crimp connectors.

Misc. shrink tubing or vinyl electrical tape

18 or 20 ga wire for controls (recycle from trailer wiring?)


Comments are encouraged as to the design. Especially if any flaws are uncovered. vic



8W42-10 wNotesRev1.jpg

8W42-11 wNotesRev1.jpg

Some other 2004 Espar Booster Heater threads which I've posted are here:

Some 2004 Espar Heater Notes

Remove Espar Heater from T1N

General Espar Heater Wiring Information

Cabin Fan Resistor Circuits

T1N Booster Heater Wireless Control
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Last edited by Aqua Puttana; 01-08-2014 at 05:32 PM.
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