compressor I chose was a York compressor, which I got out
of an AMC Eagle or Concord (or something like that) at a
junkyard. York compressors are better for on-board air since
they have their own oil reservoir, and don't let any of
the oil get into the air you're trying to compress. They
also put out more volume than other automobile compressors.
The picture to the left shows the compressor, with the mounts
still on it, as I pulled it from the car (and after I scraped
away a small portion of the grime from the mount). As you
can see, it was pretty dirty...
you pull a compressor out of a donor car, it's important
to try & get the brackets it mounted on, as well as
the hoses (or at least the fittings with a foot or so of
hose) for input and output. It's easy to get a barbed fitting
to attach to whatever hose comes off the compressor -- it's
much harder to find (after the fact) the proper fittings
that will work with the compressor. You may also need an
idler wheel for the belt, since the York compressor (at
least on the bracket set I got) doesn't adjust by itself.
will need to check two things with the compressor before
you buy it:
magnetic clutch must work. This can be tested by grounding
the compressor casing on your vehicle, and touching the
wire coming off the compressor to the (+) terminal on
your battery. The clutch should click, and the outer pulley
should now turn the inner part, and the compressor shaft
as well. When you remove power from this lead, the outer
pulley should freewheel, without turning the compressor.
compressor must turn over, and pump air. You can check
this by turning the inner portion of the pulley (or the
outer portion if you have the pulley engaged as above),
and seeing that the output hose blows air and the input
hose sucks air.
picked up my compressor at a place called "Pick-Your-Part",
in Hayward, CA for $22. I paid a dollar to get in, and had
to look around for about an hour before I found a donor
AMC car with a York compressor
I got the system up and running, a "flaw" in my
compressor became apparent: it would run for a few seconds,
and then lock up hard. It wasn't seizing, since I could
turn it backwards, but it wouldn't turn forwards. So, I
went to a different junkyard (one much closer to home) and
pulled a much newer looking York off a Volvo. Since I still
had the brackets off the original compressor, it didn't
much matter what car I got the compressor from. Total cost
(with warrantee): $40.
you can probably get away with not using an air tank, your
system will be much more functional if you have one. Plus,
it doesn't add much to the cost.
thought about a lot of options for tanks, including PVC
pipe, copper pipe, scuba tanks, soft-drink CO2 tanks, air
brake tanks from a truck, and fire extinguishers. What I
ended up getting was the one that I found first, which was
an air-brake tank off a Mac truck.
got the tank from Specialty Truck Parts in San Jose for
$15.00. They have a very wide selection of sizes to choose
from, and most of them go for between $15 and $25. They
are a truck wrecking yard (in case you hadn't figured that
tank I got is cylindrical, 6" in diameter, and about
18" long. It has a small fitting on each end, a drain
hole plug and a purge valve.
had to assemble a complicated fitting, since the fitting
on the tank was designed to use a compression fitting. If
you can get the original fitting with the tank you buy,
you'll be ahead of the game. Like the compressor, it's easy
to buy a fitting that will adapt copper tubing to a standard
Where the tank is mounted is an interesting question. There
are a number of good places on a Jeep to mount a small air
tank. One obvious place would be under the hood, on top
of the passenger-side fender, or below the battery, or wherever
else you have room under the hood in your particular Jeep.
Another good place is up inside the frame-rail, just beside
the rear driveshaft.
place I like best though (thanks, Joe) is up above the rear
differential. There's a space up there that can easily take
a tank of the above dimensions, and the differential will
never articulate that high. I have my tank mounted up there,
and although it was a pain to get it up there (working by
myself), it's in a nice spot, and I don't have to worry
about it. You can see the tank in that position above.
is where most of the money in an on-board air system usually
ends up going, and it's also where the hardest-to-find parts
are. There are a number of basic things (besides the compressor
& tank) that you need:
switch, fuse, wiring
of fittings & plumbing
go over each one of these in detail...
The Pressure Switch
pressure switch is simply an automatic on/off switch for
your compressor that determines whether the compressor should
be on or off based on the air pressure in the system. If
you use a electric compressor, it controls the motor that
runs the compressor. In the case of a York compressor (or
most other automobile A/C compressors), it controls power
to the magnetic clutch. When the switch is on, the pulley
(which is always turning when the engine is running) turns
the compressor. When the switch is off, the pulley free-wheels.
bought my pressure switch from an electrical supply store
called Consolidated Parts in San Jose. It is preset to turn
on at 95 psi, and turn off at 125 psi. It cost about $21.00.
Compressed air is one of those things that is relatively
benign up to a certain point, but can be dangerous when
it gets too compressed. The York compressor is quite capable
of pumping air to 300-400 psi. Many of the components used
in a budget on-board air system can only withstand 150 or
200 psi. If your pressure switch fails for whatever reason,
and doesn't switch off the compressor, you want a backup
fail-safe in place. That is the purpose of the safety valve.
It bleeds air out of the system when the pressure gets past
a certain point. In my case, the safety valve I got is rated
at 145 psi, which is fine for me, since my plumbing hose
and pressure gauge are both rated for 200 psi. I got it
at OSH for $12.99.
The Pressure Gauge
You could probably get away with not using a pressure gauge,
however, for the seven to ten bucks it costs you, it's a
worthwhile investment to have. I picked up a 0-200 psi gauge
with a 1/4" fitting for $10 while I was in Canada over
Christmas (which is about $7.50 in US dollars). You can
mount the gauge under the hood, or plumb an air hose through
and put it in your dash, next to the switch & light
mentioned below. Mine will be under the hood, and I may
add another one in the dash some time later.
In order for the compressor to work, you need to supply
+12 volts to the wire that controls the magnetic clutch.
This +12 should either come from a fused source in the fuse
box (preferably one that is keyed to the ignition switch
being on), or direct from the battery (with an inline fuse).
The problem with running from the battery is that if you
forget to shut the main switch off sometime, and you have
any kind of leak in the air system, your magnetic clutch
will be on while your Jeep is sitting in your driveway,
and will eventually drain the battery.
need a switch somewhere (I mounted mine right on the pressure
switch housing) that provides power to the pressure switch.
This is basically a manual override to keep the compressor
from coming on when you don't need it. Since it takes about
15 seconds to fill my tank (1.8 gallons) to 100 psi from
empty, keeping the system empty of air (at least while driving
on the street) seems like a reasonable thing to do.
Fittings & Plumbing
This is the most complicated part of the entire system,
both from the complexity of the system itself, and the cost
and difficulty of finding the parts and pieces for a reasonable
plumbing, I bought a 25 foot long 3/8" rubber air hose
at OSH (Orchard Supply Hardware) for $8.99. It has a standard
1/4" male fitting at each end, and is rated to 200
psi. This hose was cut to length to provide the connection
between the manifold and the tank. I used the fitting end
to attach to the manifold, and put a barbed connection on
the tank. I've been told that the nylon brake hoses that
big trucks use make a better tank supply hose, and they
are easy to adapt from a compression fitting to 1/4"
pipe fittings. They are more expensive than the hose I chose,
but will last much longer.
also bought a 25 foot long air hose coil, which is my main
air supply hose from the system to whatever tool I am using
(e.g., an air chuck or impact wrench or drill or die grinder
or...). This was also from OSH, and cost $6.99.
manifold is the piece (or pieces) that split the output
from the compressor to the various pieces mentions above
(pressure switch, safety valve, gauge, tank, and output).
You basically need an input (from the compressor's output)
and five outputs, to go to each of the above.
and Home Depot both sell a cool-looking cast aluminum 1
-> 3 manifold. At OSH, the price was over $8.00, and
at Home Depot, the price was $4.22. Guess where I bought
bought two of them, for a total of eight holes. Two of the
eight holes were used to join the two manifolds together.
That left six holes, which coincidentally is exactly what
I needed! You can get these manifolds in two sizes, 3/8"
and 1/4". Since all of my plumbing (except the hoses)
are 1/4", I got that size. Even on the 3/8" hose,
the end connectors are 1/4".
in addition to the manifolds, I bought:
3/8" barbed->1/4" threaded fittings (OSH,
small hose clamps for above barbed fittings (OSH - $0.99
brass 3" straight extender (since the pressure switch
I bought is so big, you want to mount it above all the
other stuff sticking out of the manifolds - OSH, $1.35)
brass 2" straight extender (to provide a male fitting
for the quick-disconnect - OSH, $0.99)
brass 1" straight extender (to connect the two manifolds
together - OSH, $0.99)
quick-disconnect plug & socket pairs (OSH - $2.72
male/male joiner (a joiner that joins two male fittings
-- OSH - $0.99)
on what the hardware on your tank looks like, you may
need a couple other fittings to connect the supply hose
to the tank, and possibly plug one or more other fittings
on the tank.
air chuck (OSH - $2.25)
roll Teflon tape to make air-tight connections (OSH, $0.99)
in all, the hardware cost about $95.00, bringing the total
to about $150.
I collected all the parts, I began the task of putting
it all together. This is considerably harder than it sounds,
and involved numerous trips to the hardware store/junkyard,
to collect odd parts and tools.
first step was to get the compressor mounted, and functioning
with the other accessories (water pump/fan and alternator
on my engine). The brackets I got with my original compressor
made the job somewhat simpler. With this setup, the compressor
is put where the alternator used to be, and the alternator
is put below the compressor. The drive belt now runs the
compressor, and the second pully on the compressor drives
the alternator, on a seperate short belt.
first problem that I ran into was how to tension the belt
that runs the compressor. The alternator was mounted on
a swing bracket, and this could adjust the belt in the
old system. The compressor was solid mounted, so a secondary
mechanism was needed.
thought about slotting the compressor mount holes, to
allow the compressor to slide, but there was a problem
with that approach. On my engine, the thermostat housing
was directly in line between the top of the compressor
pulley and the top of the fan/water pump pulley. Thus,
I determined that I would need an idler pulley to both
tension the belt, and get it out of the way of the thermostat
decided to use a pulley that would press the belt in,
since if I put the idler pulley on the inside, there wouldn't
be enough of the fan pulley grabbing the belt to work.
This required a flat idler pulley, which of course I didn't
have (the idler pulley I got with the compressor was a
v-belt pulley, so I assume the six-cylinder system must
be a little different that my four-banger).
I went off to the junkyard, and for $5 grabbed the first
flat idler pulley I found, which happended to be the timing
belt idler inside the engine of a VW Rabbit. The bolt
hole was eccentric from the pulley, so you could rotate
the center of the pulley to change the tension. Perfect.
I got a piece of 2" x 3/16" flat iron bar, 12"
long (OSH, about $1.50), and drilled a few holes in it.
It mounts to two bolts in the alternator mount assembler,
and tensions the belt nicely.
that was set up, I started up the engine, to make sure
nothing would explode or take off, and engaged the magnetic
clutch on the compressor to make sure everything worked
okay (it did).
then took a small piece (1" long) of aluminum angle-iron
(left-over from my battery tray project), drilled a 1/2"
hole in one side, and a 1/4" hole in the other. This
would be the mount for my manifolds, which held all the
good stuff. I countersunk the 1/4" hole, so I could
use a flat-head screw to attach it to my inner (under-the-hood)
took the two manifolds, used a 1" brass extension,
and a couple of spacer washers, and the angle-iron mount,
and screwed it together, using teflon tape on the threads.
I then attached the accessories, one by one, to the various
holes in the manifolds. On one side, I put the pressure
switch (on a 2" extension), the input from the compressor
(using a barbed fitting & hose clamp), and the output
to the tank (I used the fitting on the end of the hose).
On the other side, I put the safety valve, the pressure
gauge, and a female quick-disconnect (using a 2"
extension, since the manifold and the quick-disconnect
were both female attachments). All the threaded fittings
were wrapped with teflon tape before attachment.
hooked up the tank (just laying on the garage floor for
now), and put a jumper cable from the battery to the pressure
switch and from the switch to the compressor. Voila, instant
the coiled hose (yellow, in the picture below) I used
a male-male joiner to connect the male plug of the quick-disconnect
fitting to the hose, and the second female quick-disconnect
plug fit on the other side directly. The air chuck threaded
directly onto the second male quick-disconnect plug.
came the wiring. I ran a wire from the fuse panel through
the firewall, back to the pressure switch. This supplied
power to the system. I drilled a hole in the pressure
switch housing, and attached a small lighted rocker switch
I bought at Radio Shack. Power went to this switch, and
then to the "line" side of the pressure switch,
and then out to the compressor from the "motor"
side of the pressure switch. All the attachments were
done using crimped stak-ons.
Finally, I mounted the tank up over the differential,
using a couple big U-bolts that came with the tank, and
drilling up through the floor into the "bed"
in the back of the Jeep. I ran the hose back from the
manifold, along the inside of the frame-rail, and attached
it to the tank using a barbed fitting with a hose-clamp.
And, that was that.