Have you checked your tire pressure lately?
85 percent of all tire air pressure losses are the result of slow leaks that occur over a period of hours, days, or months.NHTSA
I’m also guilty of not checking tire pressure as often as I should. As I started thinking transitioning to an RV-based lifestyle I had nasty visions of attempting to finagle the truck and trailer combination into gas stations to check the tire pressure. I’d rather not do that.
I had already put an on-board air compressor on the Jeep I used to own. I knew that decent-quality 12v pumps were now available for under $100. I set out to outfit our tow vehicle with a similar setup.
In this post I’ll show what it took to install a 12V onboard air compressor on our 2002 Chevy Silverado 2500 with the 8.1L gas engine.
Hardmount or Portable?
You could just carry the 12V compressor in a bag and get it all out when you needed it.
I wanted a more permanent installation that would make it easier and quicker to use.
- The pump mounted away under the hood
- A dash-mounted switch to turn it on
- An exterior-mounted air connection to hook an air hose to
Do you lose portability this way? I don’t think so - I can either just string a long hose or move the truck close to where the pump is needed.
Overall the process requires the following steps:
- Sourcing the Air Compressor
- Adapting the Air Compressor
- Mounting the Air Compressor
- Wiring up the Air Compressor
- Plumbing an air outlet in the truck bumper
- Creating an inflation tool
Sourcing the Air Compressor
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These pumps have been around for a couple of years and are well-liked by the off-road community where tire pressure changes are frequent.
The unit is reasonably priced at $60 - $80 and is easily adapted for different situations.
They have some faults but the fixes are well-documented in these discussion forum threads.
Adapting the Compressor
Our Chevy truck had a nice large open spot under the hood so I adapted the unit for permanent mount by:
- Removing the handle.
- Removing the gauge and plugging the hole left behind.
- Removing the rubber feet to enable those spots to be used for screws.
- Modifying the wiring to bypass the included switch (I siliconed it over hoping to keep the wiring out of the elements).
- Inspecting the connections to the compressor’s relay and fixing one cold solder connection.
- Changed the wiring so the positive side would be switched instead of the negative (so the load would light up an illuminated dash switch).
The last step was figuring out what to do for an air outlet.
The threads on the compressors main outlet are non-standard, so I couldn’t easily remove the male fitting and hard-connect an airline.
I settled for this arrangement - a quick connect coupled to a tee, with a adjustable pressure-relief valve on one output and the other outlet used to connect the air line:
Let it Bleed
This is a tankless air compressor designed to always pump air.
This is not how normal residential or industrial air compressors work. Normal compressors only move air when an airtool is running or you are inflating a tire.
When that isn’t happening, the air pressure “backs up” to fill a tank. Once the tank is full there is both a switch mechanism to turn off the pump and a safety release valve that pops before the tank explodes.
By changing this compressor to use standard air hoses and fittings it needed a way to bleed off excess pressure. That’s what the adjustable pressure-relief valve does. Of all my tires my road bike tires needed the highest PSI at 90 - so I set the valve to begin to bleed at just over 90 PSI.
Mounting the Compressor
The compressor fit into the target spot almost like it was designed to fit there. It nestles under the fender support, and one of the mounting holes actually lined up with a hole already in the fender:
The pump is narrow enough to allow room for the hood spring when the hood is closed:
I was only able to get 3 feet mounted, as the front inner one ended up directly under the hood/fender support. I used both double lockwashers and Loc-tite on the 3 feet I did mount, so I’m hoping that works well enough.
Wiring the Air Compressor
Wiring up the air compressor is really two jobs - the dash side and the underhood side.
Truck Dash Wiring
The truck’s original stereo had both a CD/FM headunit with a remote cassette deck mounted further down in the console. The headunit has been replaced with an aftermarket version which left the cassette deck inoperable.
I removed the cassette deck, and used its mount to create a switch panel big enough for two switches with paired-up fuses (the 2nd set for auxiliary back up lights):
The switch panel slides into place like the original cassette deck did - making wiring an easy chore:
Once in place it ended up looking good:
From there I sourced power under the truck’s hood (the ‘02 Chevy has a remote jumper cable connection point that worked well) and ran the loom across the firewall:
In my box of spare 12v parts I found a distribution block big enough to handle the 12v power, the trigger power from the dash switches (that connect to relays), and the ground connections for both the air compressor and auxiliary lights:
Plumbing an Air Outlet in the Truck Bumper
Once the pump was mounted I ran flexible rubber air line down the truck’s frame to the rear bumper. I drilled a hole through next to the license place for the air outlet - figuring this spot would be usually half-way between truck and trailer tires. It’ll also be handy for airing up bike tires.
I had to use some washers to space out the connection for a good seal. I bought stainless washers so they won’t rust.
The Inflation Tool
This is a leftover from my Jeeping days - an inflation tool consisting of a plumbing valve, to a three-way manifold, to a pressure gauge and then to a “whip-hose” (which has an flexible end), to a clip-on chuck:
The benefit of this tool is that you can clip the chuck onto the tire and then stand up. The hose allows for some flexibility, and to check the tire pressure you just clip the valve handle.
The gauge then reads what the tire has, so there is no need to disconnect the compressor to check pressure. The gauge is large and much easier to read than the pencil type gauges.
The basic process is:
- Get the hose out and get everything connected
- Switch on the compressor
- Begin inflating
- Flip the valve lever to check pressure
- When it’s correct leave it flipped
- Disconnect the chuck and move to the next tire
The compressor can be left running, as once it reaches roughly 95 PSI the adjustable relief valve will start bleeding pressure off. This protects the compressor from reaching its limit and shutting down or overloading.
Field Use Review
This unit has served us well for 6 plus years on the road.
It’s aired up countless bike tires, topped off truck and trailer tires, and gotten comments from Discount Tire guys all across the country.
Once in a while on a long fill it will overheat and shut down. Opening the hood helps ventilate the unit but sometimes the extra noise isn’t a good thing for the neighbors.
Also once in a while it hasn’t started pumping when turned on - I had to bang on the pump to get it going. I assume it got dirty from living under the hood. I sprayed it down with silicone and now make sure to turn it on for a second or two every now and then.
It’s been well worth the time invested to know I can monitor my tire pressures easily.
How do you manage your tire pressure while traveling?