Article and photo's courtesy of Jeff Holsted
One of the first things some people do before they hit the
trails is air down the tires. It's really easy to do, but what about
airing back up? There are several options for on-board air on the trails.
Here are a few options:
Bring a portable air tank with you. Should be good for a
few fills, but won't help if you're gone for a while with no way to air
the tank back up.
Carry a small compressor powered by the lighter jack.
It's good for emergencies, but takes a long time to fill a large tire.
Some companies sell portable compressors that are made to fill up tires
fast, but most won't run air tools, and they are generally over $200.00.
But, they are relatively simple to install, and very little if any
fabricating will be required.
Bring a C02 tank. These are much better than
the smaller portable air tanks, and will fill lots of tires, and run air
tools, but you have to get it filled when it gets empty. And some can cost
more than the portable compressors.
Run a compressor off of the engine.
This supplies large amounts of air, is fast enough to run air tools, and
will always work as long as the engine is running. The compressor is also
fairly inexpensive. But, most likely, a bracket will have to be made to
mount the compressor to the engine because there are so many different
accessory and belt configurations available for GM vehicles.
Out of all
these options, I chose to do an engine driven compressor. The cost, as
well as the constant supply of air, were the main benefits. The most
common compressor for this type of setup is the York-style compressor. It
can be found on Ford, Volvo, AMC, IH, and Oldsmobile vehicles from the
late 70's to the early 80's.
Why a York? The compressors found on most
vehicles with A/C are lubricated internally, by the freon in the system.
For pumping air, you would have to have an external oiler to keep the
compressor lubricated, and a filter to remove the oil from the output of
the compressor. With a York, this is not necessary. It has it's own
internal reservoir for oil, making it a much better choice for pumping
air. However, there are many variables when considering which style of
York to use. There are three different displacements or strokes available,
as well as many different types of hose connections.
Which one do I get?
Of the three different stroke models, the long stroke York is the most
desirable. The longer the stroke, the bigger volume of air pumped per
minute. The easiest way to determine the output or stroke of the
compressor is to look at the crankshaft. To get to the crankshaft, you
must remove the pulley. This can be done by removing the bolt and washer
holding the pulley on, and running a 5/8" coarse thread bolt in to
force the pulley off. All models have a flat end on the crankshaft; the
edges of the crankshaft are what's important. A beveled edge on the end is
the short stroke. If it has a sharp corner, but is grooved for a retaining
clip, it's a medium stroke. And if it is a sharp corner without any
grooves, it's a long stroke. If the compressor still has the original
Motorcraft metal tag bolted to it, you can use that for reference also. It
will have a series of five numbers/letters. The last three are the
displacement, and direction. Of those last three digits, the last letter
is the output direction and the other two are the stroke. The three stroke
numbers are: 10 = long stroke, 09 = medium stroke, 07 = short stroke. The
Discharge Direction letters are: L = left, R = right. So if it's a **09R,
then it's a medium stroke with a right side discharge.
But, the tag is not
the best way to identify which model is on the vehicle, because it's
common to replace the tag when the compressor is serviced. The tag on my
compressor was not the original, and the numbers didn't match any factory
output numbers. The single best way to identify the model is to remove the
Of the vehicles that used York
compressors, the long stroke model is most common in late 70's to early
80's Volvos. There is not much information about which models were common
on AMC's or Fords, but most people I asked seemed to agree that most
Volvos were usually long stroke. I didn't want to spend all day at the
junkyard looking for compressors, and just concentrating on finding a
Volvo made the search much easier. The hose connectors can also be a
factor when looking for the right compressor. Volvo and AMC-style hose
connectors, run horizontally across the top of the compressor. Ford-style
connectors stick straight up out of the top of the compressor and then
connect to the A/C system. This can make the overall height of the unit a
little taller. The different connector styles are interchangeable, but
finding fittings for the factory A/C connectors is difficult, because the
threads don't match common pipe fittings. Fortunately, onboardair.com
makes custom flange fittings that use a common 1/2"npt, and they are
a direct replacement for the factory fittings. There are also several
different types of heads found on the York compressor, but the two most
common are the Flange style or the tube "0" or rotolock style.
The compressor I found was out of an 81 Volvo, and had flange style
fittings. There are also several different variations of pulley/clutch
assemblies found on York compressors. Depending on your particular
application, it may be beneficial to get a few different compressors to
mix and match the pulleys. New or Used? After deciding on which model to
get, I was curious to see how much a new compressor would be. After making
a few phone calls, the $200+ I was being quoted was more than the $150 I
had budgeted for the whole project, so I decided to get a used one. I made
a few calls and the prices ranged from $30 to $75 depending on who pulled
it. I picked up my compressor for $35 with a 1-month warranty from the
local junkyard. I would highly recommend pulling it yourself. It may be a
pain to get out depending on the vehicle, but that will give you an
opportunity to grab some of the brackets and the hoses, which you will
need later. Before you spend your hard-earned money, you need to test the
compressor to see if it works.
There are two things to test for: 1. If the
clutch works, and 2. If the compressor pumps air. To test the clutch, look
for a single wire coming out of the compressor. This is the wire that is
normally connected to the A/C switch on the vehicle, and controls the
clutch/pulley assembly. When the wire receives power, it "locks"
the clutch, and turns the crankshaft on the compressor. The outer part of
the pulley assembly is always turning when the engine is running, and it
should spin freely. The inner part of the pulley is what actually makes
the compressor turn. To test the clutch, ground the compressor, and touch
the single wire to a positive battery terminal. You should hear a
"click" when you apply power to the wire. This "click"
is the outer part of the pulley, locking to the inner part on the
crankshaft. You should be able to turn the pulley with it locked and be
able to hear air being pumped. It should also be harder to turn because of
this. Also, when you remove the wire, you should hear a "click"
again, and the outer part of the pulley should disengage and spin freely
again. It is also a good idea to plug one of the hoses with your thumb and
turn the crankshaft (inner part of the pulley) with or without the clutch
being engaged. Depending on which direction it's turned, it should either
suck or blow air against your thumb. It's a good idea to turn it both ways
just to be sure it works. If the compressor fails either of these two
tests, it has internal damage, or a bad clutch. New clutches aren't cheap,
so be sure to get one that works.
How do I mount it? This is probably the
hardest part of the whole on-board air project. As of now, there are no
brackets mass-produced to mount a York on a Chevy V8. You will have to
make one, or find someone to make it. I used part of the original Volvo
bracket, and made my own adjustable mounts out of 1/4" steel plate. I
wanted to keep the factory A/C for now, so I mounted it right next to my
factory compressor. I also had a spare slot on the pulley from the water
pump that would allow me to mount the compressor without needing to use an
idler pulley to maintain tension on the belt. The compressor MUST be
mounted in the vertical position or as close to vertical as possible. If
not, the oil will spill out of the reservoir and get in the air lines. If
your engine uses serpentine belts, onboardair.com also has a
serpentine/v-belt combination pulley for alternators that will allow you
to run a v-belt to the compressor. It might work with a Chevy alternator,
but I'm not sure.
York compressor installed
compressor lubricated. The quickest way to burn up a York is to let it run
out of oil. Since it's not pumping freon anymore, you have to keep it
oiled. The compressor has an oil fill/check hole on the side about half
way up. It has a capacity of about 12 ounces. To measure the oil, I had to
come up with a dipstick. You can make your own out of a coat hanger, or
buy one from onboardair.com. I made one following Ben Hollingsworths
directions on his website: click
I made sure all of the old oil was drained from the compressor before I
hooked it up. This required removing the head, and letting it sit upside
down for a few hours.
After cleaning it out, I filled the compressor with
10W-30 motor oil and started hooking up the switch and air lines. Air tank
The next step was to find and install an air tank somewhere on the blazer.
Having an air tank for storage is essential if you plan on running air
tools, and it makes for faster fills on tires. There are a few companies
that sell small air tanks that are rated for high pressure (up to 150 psi.)
for around $60 or $70. Small air tanks are also common on large trucks
that have air brakes. Once again, I tried to save some cash, and decided
to look at the salvage yards. I found a 2.5 gallon tank w/brackets at a
semi salvage yard for $15 that was rated for 150 psi. and had several
3/8" NPT ports. I put a 140 psi. pop-off valve in the tank and
plugged the holes not used. The tank was bolted to the floor of the blazer
under the rear seat.
|Air tank installed
and air fittings. After installing the air tank, the final steps were to
build the pressure switch assembly, and mount it to the fender. A pressure
switch is necessary to control the compressor. It turns on the compressor
when the pressure drops below 90-95psi and turns it off when it reaches
125 psi. This keeps it from running constantly and setting off the safety
valve on the tank. I also installed a master switch inside the ash tray to
control power to the pressure switch. If the system were to leak down
overnight, the pressure switch would turn on, creating an open circuit, if
it was wired directly to the battery. It would be possible to just wire
the pressure switch to a remote wire, that was on only when the vehicle
was on, but I like the extra convenience of being able to turn it on when
I want. The pressure switch is a SquareD model #FHG12J52X. It comes with
or without an unloader. My local hardware store just happened to have one
with an unloader, so that's what I got. The unloader relieves the pressure
on the pump when it stops, allowing it to start back up a little easier.
The flange fittings for the intake and output
ports on theYork came from onboardair.com. Their fittings make setting up
the air hoses much easier because the threads are a standard size, and
most of the fittings I needed could be found at a local hardware store.
For the intake filter, I used an exhaust muffler from Grainger (part
#1A328). It's compact and mounts directly to the flange fitting. For the
output side I used a braided line from Grainger (part #4HM96) to connect
the compressor to the switch assembly. It may be overkill, but the output
temperature on a York can get well over 300 degrees if the compressor is
run for long periods of time. Temperatures that high will melt most rubber
line and the braided line is rated for 500 degrees. The line from the
compressor runs into a one way valve, to stop air from coming back into
the compressor, when it shuts off.
Then I installed the pressure switch,
and hooked the unloader port of the pressure switch to the check valve.
After the switch is a pressure gauge rated at 150 psi and then a 1/4"
NPT "T" fitting with a quick-disconnect for the air line up
front. I then ran a line from the "T" to the tank under the rear
seat of my Blazer. I also ran a line to the back of the blazer with
another quick-disconnect. Here is a diagram for the whole system.
How it works. Great!! This was one of the cheapest, and biggest
bang-for-the-buck modifications I have done to my blazer in a long time. I
have around $150 invested in it, and I don't have to spend another dime on
it, ever. I decided to run some tests to see how fast it would fill tires
and if it could really run air tools. My first test was to air down a
35" BFG MT to 12 psi, then fill it back up to 33psi. The total time
on the fill was about 45 seconds. Tank fill time is just under 40 seconds,
considerably faster than most portable compressors. The compressor pumps
air faster or slower depending on the speed of the engine, and the pulley
sizes used. Most of the time, when I'm using it, the Blazer is at idle
(700-800 RPM, it's not recommended to run the compressor over 1200-1300
RPM's for a long period of time). I then grabbed my impact and proceeded
to remove all eight lugnuts on my front wheel without a hitch, never
having to stop to let the compressor fill up. It also can supply enough
air to run grinders and ratchets, maybe not as well as a 60 gallon 2 stage
compressor, but good enough to make emergency trail repairs.
change anything? If I ever ditch the factory A/C, I will probably make a
new bracket, just to get the compressor mounted directly to the motor. I
haven't had any problems so far, but I hate to waste the space if I don't
plan on running the factory A/C. I also plan on installing a hand throttle
to get the engine RPM a little higher when the compressor's running. I
have also thought about adding at least one more tank to the system, for
just a little more storage. I would highly recommend a York to anyone
wanting to add on-board air to their vehicle. It's relatively inexpensive,
and definitely trouble free.
Part's used and part numbers:
pressure switch #: FHG12J52X (125 psi max w/30 psi differential, and
unloader) onboardair.com: Flange fittings for York 1/2" NPT
Grainger parts: Filter/muffler 1/2" NPT #: 1A328
Teflon Braided Line 5/16" x 18" (9/16" ends) #: 4HM96
Adapters for teflon line 9/16" x 18 to 3/8" #: 4HM27