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I feel like there are quite a few good Espar D2 installations documented out there, but that those going the hydronic D5 route are still underserved. This post aims to start correcting that by following up on a more overarching one that I previously posted. I hope my previous post illustrates what this system even is and if you’re interested in exploring it enough to care about these details.

Here I will just try to touch on a few of the vague points I felt were not clear or not as prominent as I expected in the documentation.

First things first… we’re aiming for a result like that shown in the middle picture below. For reference, this is (of course under the van) behind the fuel tank fill, on the outside wall, behind the driver seat. When you jump under your van, it should look pretty familiar. The left picture, looking forward, should be particularly orienting. You don’t have to put it there, but many do for various reasons… fuel lines, exhaust, and other items like grey water tanks, etc.

Espar D5 pics from left to right… bracket, full install, rivnuts (courtesy of Sandor Lengyel)

My extensive photos are in an album here.

Some things that weren’t immediately clear to me became clear after some communication with the community. I’d like to offer a special thanks to Aaron Silidker among others on the Sprinter Build Out International Facebook group for helping to clarify some of these details.

Some links for the user manuals:

This is perhaps the most useful picture from the Espar Hydronic II D5S manual…

Exploded Diagram from the Hydronic II D5S User Manual

Where the legend for the numbers and letters are as…

Label Legend

And this cheat sheet of bullets should speed some comprehension up…

  • The two water pump (15) wires go into the main 10-pin harness shown middle right in the above diagram. Chambers 8 and 9 to be exact.
  • The fuel pump and water pump both have crazy long wires that you can almost certainly shorten up (probably so long for the 18-wheeler folks out there or something).
  • The blower relay (B, C, 22, 23) is set aside by many folks, even some of those using their D5 for both air and water heat. You can probably use your thermostat to start your blowers and to tell the D5 to check to see if the coolant temp has dropped too low. In summer you’ll want a way to just do the latter in order to facilitate the creation of hot water only (no hot air / blower activation).
  • E and F can be disregarded for most folks.
  • The kit comes with and uses unique connectors, which need a unique crimper… not just your normal AWG crimpers. These can be found on Amazon using this link.
  • It’s typical practice to put the electrical bits like the diagnosis port, fuses, etc. in the van cabin.
  • I’m finding the vertical fit a bit tight (coolant lines get near the ribs and exhaust line starts to show), so I’m getting a fancy 90 degree elbow to decrease how much the exhaust hangs down…
SS elbow to decrease overall height… because I’m OCD

This fitting solves 2 problems at once… a.) it provides a mean for any condensation in the exhaust to drain out and b.) it makes the install a little more low profile in the vertical direction. This image shows how, if you fail to push the unit all the way up to the van floor, that you kinda sorta run out of vertical room… or your exhaust ends up decreasing your ground clearance…

  • A high altitude kit is basically just wired in series between the group of wires labelled “A” above and your controller. Yellow (ground) and red (+12v signal) are used to tell the brain of the D5 to wake up. The D5 “waking up” means it will start pumping coolant. If the coolant is below the internal set point (see the manuals for details) it will fire up. It will looks something like…
High Altitude Kit just goes between heater and controller, at least on 4 wires
  • Lastly, Aaron mentioned that you get 3 chances to start up the unit before it throws an error code, if the fuel is not properly going through. For this reason, I put together a little low brow siphon… it cost like $15 to put together from O’Reilly (the hand siphon) and Ace Hardware parts (2 hose barbs + union). It is shown below. I’ll use it to pull fuel past the fuel pump before I go to fire it up. If this approach fails you and the heater locks you out due to failing to start, power cycling it by pulling the fuse should reset the issue.
Hand bulb with a hose barb adaption from Ace… clear line shown in the 2 pictures is the same clear line. You put the hose barb into your fuel line and use the bulb to pull fuel through.

If someone knows of good documentation about tying into the main engine coolant, please let me know, so I can link this to that. I will at least provide this link about the 6-way valve as food for thought on that front.

This post still needs significant cleanup, but I wanted to at least start getting some notes jotted down, to improve upon.