Viair 420C Compressor Install: Part 1

Although the trails we drive are not up to Rubicon-esque standards, we frequently encounter loose surfaces, embedded boulders and other obstancles which necessitate airing-down our tires to provide as large a contact patch as possible. This greatly improves traction and makes for a much more comfortable ride. I recently purchased a Viair 420C compressor and am hard-mounting it into the 2nd battery compartment of my Land Rover LR3.

The Viair 420C is a 33% duty cycle compressor (runs for 15 minutes, then cools for 30 minutes), pushes 2.54 CFM and draws 30 amps. It's a sealed unit designed for exterior use on 4WD vehicles and the kit includes almost everything you need to mount it.

I had the Land Rover dealer run a 10-gauge accessory line from the existing battery to the second battery compartment with a 40 amp inline fuse. They did a very clean job and followed the existing harness routing, so there is no unnecessarily exposed wiring. In order to position the compressor, I set it in the battery compartment and made sure there was plenty of clearance all the way around. With the compressor positioned, I dipped the flat side of a bamboo skewer in white paint, then slid it through the mounting holes and marked the bottom of the battery box. This ensured the mounting holes were perfectly positioned and eliminated the possibility of measurement errors.

I removed the compressor and drilled a 5/16" hole through each of the marked positions. This was just big enough to fit the brass threaded inserts to anchor the compressor. I chose these inserts because the compartment for the second battery is shared with the ABS system and I was concerned that without a firm anchor, the compressor could break loose and damage the system. Using a steel dowel and 5-lb sledgehammer, I drove each of the inserts into the plastic bottom of the battery box. The inserts now sit totally flush with the bottom of the compartment and as a side benefit, they give the installation a completely 'stock' look. The compartment already has a number of threaded brass inserts molded into it for the battery-mounting hardware, so if I ever remove the compressor, the compartment won't look like there are a bunch of random holes drilled into it.

With the brass inserts installed (and my heart rate back to normal - it's not easy to drill holes in a brand-new truck!) I inserted the screws and washers through the mounting holes on the compressor and positioned it in the box. Here's a tip - with the screws and washers on the compressor, the lower washers will fall off when you turn it over to mount it since there is nothing to hold them in place. I wrapped a very small piece of teflon tape around the threads of each screw to keep the washers from sliding off.

The threads cut through the tape as they are secured into the anchors and the tape won't interfere with the mountings. One last note: The body of the LR3 sits very close to the bottom of the battery compartment, so I had to remove about 1/8" from the passenger-side front screw. This allowed me to tighten the screw firmly without any risk of hitting the body below the tray. With the compressor secured, it is practically impossible for it to break loose and there is absolutely no movement of the unit inside the compartment.

I routed the ground wire from the unit to a chassis ground lug located inside the battery box.



The top of the box has plenty of room to seal, I can replace the air filters without removing anything and none of the hoses or wires are routed near any hot components. All that's left is to wire it up and mount the air source quick-connector!