Mercedes Sprinter on-board air system mount

Mercedes Sprinter on-board air system mount

Van Compass Mercedes Sprinter Air system mount


Version 1.0

General Notes

  • This blog post covers the routing and plumbing of a Viar onboard air system on the Van Compass 2015 4x4 Mercedes Sprinter Van.
  • For detailed instructions of the air system mount bracket installation, refer to 4026 Instructions.
  • We tried to utilize complete Viar Kits for installation on our test van for simplicity and ease of documentation. This air system could be wired and plumbed in a number of different ways using various different styles of connectors, this blog post is to be used as a guide and to share how we mount an air system installed in house at Van Compass. 


Parts List Utilized for Complete Air System Install


  • (1) 4026 Van Compass Air System Mount
  • (1) 91022 Viar 2.0 Gallon Air Tank
  • (1) 45042 Viar 450H Air Compressor
  • (1) 90005 Viar Tank Port Fitting Kit
  • (1) 20053 Viar Onboard Air Hookup Kit (85PSI on / 105 PSI off)
  • (1) 90007 Viar Air Source Relocation Kit
  • (1) 92814 Viar ¼” NPT Quick Connect Coupler (Female)
  • (1) ¼” NPT Male – Male Nipple
  • (2) ¼” NPT Bulkhead fitting


Tools Needed for Air System Plumbing / Wiring:


  • Heat Gun
  • Drill with quality metal cutting drill bits.
  • Simple hand tools:
    • Basic wrench and socket set:
      • SAE sizes: 7/16” – ½”
      • Metric Sizes: 10mm, 12mm, 13mm
      • T-25 Torx
    • Wiring tools:
      • Crimp connectors; Male and Female Spade, 12-14 gauge
      • Heat shrink tubing (Optional)

Approximate Installation Time

  • 4-6 hours



With the Van Compass 4026 Air System Mount installed in the engine compartment, we can fit a 2.0 gallon Viar air tank and choose from a plethora of Viar or ARB compressors to pair along with it for a capable, reliable onboard air system.  Mounting the on-board air system under the hood is beneficial for two reasons;

  1. The onboard air system is isolated from the interior cabin compartment which equates to less noise and vibration in the cabin compartment for a more luxurious adventure van experience.
  2. The onboard air system is protected from the elements which increases longevity and reliability of the air system.

Step one after fitting the 4026 Air System Mount to the vehicle is to choose and mount an air compressor.  We won’t go into much detail as to what size air compressor is necessary for your application, but a general rule of thumb with on-board air systems is that bigger is usually better.  No one has ever disappointed by having too much CFM in an air system, at least not in our experiences.  We choose an air compressor that could easily keep up with inflating our 35” General AT2 tires which are equipped on our test van.  With this in mind, we decided to run a Viar 450H compressor. 

The 450H has a 100% duty cycle at 100psi.  Meaning it can safely run all day long at 100PSI without damaging itself.  It has a max working pressure of 150 psi and is capable of outputting 1.8 CFM of air pressure.  Paired with the 2.0 gallon reserve tank, this should easily be able to keep up with inflating all 4 tires on our big 4x4 van after a fun day in the dirt. 

The Viar 450H compressor kit. 

            We start installation by fitting the 450H to the 4026 Air System mount.  Take note of the holes to utilize by referencing the dimension drawing at the end of the 4026 Installation instructions.  This is the drawing to use to aide in which holes to use depending on the compressor chosen.

Van Compass Mercedes Sprinter air system mount

            Most Viar compressors and air tanks install using M6 bolts that necessitate a 10mm socket / wrench for installation.  Refer to instructions included with your Viar components for hardware utilization. 

            After the compressor is installed, prepare the Viar 2.0 gallon air tank for installation by first installing the rubber feet / isolators into the mounting brackets of the air tank.  Install the brass sleeve through the isolators once they are installed in the air tank.  Lubrication is your friend when it comes to installing these rubber isolators.  We prefer using liberal amounts of Windex on the rubber isolators.  Next, plug the rear ports on the tank and install the lower petcock.  We used Viar part number 90005 Tank Port Fitting Kit which includes the following components:  

– (2) 1/4″ NPT Plugs

– 1/4″ NPT Drain Cock

– 1/4″ NPT Compression Fitting

– 250 PSI Safety Valve (P/N 90004)

– 175 PSI Safety Valve (P/N 90005)

            We installed the two ¼” NPT plugs in the rear of the tank and fitted the ¼” NPT Drain Cock on the port on the underside of the tank.  Be sure to use thread sealant or Teflon tape to seal all NPT fittings during installation. 

With the rear ports plugged and the drain cock installed on the underside of the tank, fit the tank to the vehicle.  Install the tank so the open ports are towards the front of the vehicle as shown below.  Utilize the M6 hardware included with the 2.0 gallon air tank kit and bolt the air tank to the 4026 Van Compass Air System Mount in the vehicle.

Van Compass Mercedes sprinter on board air compressor mount

            To plumb the air compressor to the air tank, we utilized the 20053 Viar Onboard Air Hookup Kit which includes a number of components to utilize in completing a clean, reliable installation.  The great thing about the Onboard air hookup kit from Viar is that it takes a lot of the guesswork out in both wiring and plumbing.  This kit includes a pressure switch with built in relay that features clearly labeled wiring and instructions on how to hook everything up so that the air compressor shuts off once the air system builds up to 105 PSI of pressure.  The compressor will automatically kick back on once the pressure depletes to 85 PSI.  This makes for an air system that is super convenient to use and efficient. 

At this point, we should mention that pretty much all Viar port fittings are ¼” NPT.  The one component missing from the Viar kits which we needed to source was a ¼” NPT Male / Male nipple.  We used this to thread into the top port of the air tank. 

With this threaded into the top of the tank, we then threaded ¼” NPT female T-fitting included with the Onboard Air Hookup kit.  With the T-threaded into place, we fit the included ¼” Quick Connect Coupler to one side of the T-fitting and the pressure switch into the opposing side of the T-fitting.  Note, the pressure switch features an 1/8” NPT male thread on is, so utilize the ¼” NPT to 1/8” NPT reducer from the Viar kit for proper installation. See image below for reference.

Sprinter onboard air

            Something to consider at this time is to make sure all the plumbing is going to clear the windshield wiper linkage.  Make sure the T-fitting is positioned similar to how it is pictured above.  It works best if it is close to parallel with the firewall.  It’s a good idea to turn the wipers on and watch how the linkage moves in this area under the cowl of the van to ensure no interference could occur. 

            Next we can start plumbing air lines.  We utilized the ¼” air line tubing and compression fittings included with the Viar kits.  Step one in this process is to straighten out the nylon air lines.  We used a heat gun and warmed the tubing while pulling it tight to get the air line to lay flatter so it was much easier to work with. 

We installed the ¼” NPT Compression fittings included in the Air Hookup Kit in the front ports of the air tank.  We used the T-fitting on the outer fitting but needed to clearance a small piece of plastic ribbing on the back side of the grill to not kink the air line.  A better solution in this location would be a 90 deg ¼” NPT compression fitting and place the Viar T-fitting at the inner port. 

When installing the air line onto the compression fittings, use a heat gun to soften up the air line material where it is to be fitted over the barb on the fitting.  Make sure the compression nut is installed on the airline prior to fitment.

Air line routing and quick connect coupler locations are really up to the installer but we prefer two locations; one at the front of the van near the front step and the other inside the van near the back door. 

A minimum of 20 ft of air line is needed to get to the rear of the van if you choose to mount the quick coupler as pictured above.  Use the 20ft of line from the Air Hookup Kit for the rear air line, and the 15ft of line from the Air Source Relocation Kit to run the front air line and in-cab gauge line.

We plumbed our tank as pictured below;

We chose to utilize the air pressure gauge and on / off switch from the Onboard Air Hookup Kit by mounting it on the dash of the vehicle just under the headlight switch.  To access the lower left panel of the dash, locate and remove the T-25 torx head bolt just above the OBD port cover. 

With the lower screw removed, you can pull the outer panel straight back, away from the dash and free it from the plastic clips securing the top of the panel to the dash.  With the panel removed, you can fit the gauge in this panel and run air line to it easily.  For running wiring and air line into the cabin, we poked through a small rubber plug located between the brake booster and the air tank.

Mercedes sprinter air compressor

At this point, wiring is really going to vary per vehicle.  Our van has an auxiliary fuse panel which we tied the air compressor wiring into.  However, with the wiring included in the Viar kits, you can easily just tie in to the battery directly using their included 30 Amp inline fuse wiring kit.  There are sufficient compression fittings included in the listed Viar kits to complete the front / rear air coupler installations.  The one remaining fitting not included in the Viar kits which we find useful are a pair of  ¼” NPT bulkhead fitting to properly secure the quick couplers to their respective mounting locations.

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