York OBA for a Small
Some of the benefits of a York
compressor-based on board air system include the cost and the constant
supply of air. The most common compressor for this type of setup, the
York-style compressor, 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 its 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 York is best? 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 pulley.
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 Volvos were usually long stroke.
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,
www.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.
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? New compressors are usually in the
$200+ range. Used prices normally range from $30 to $75 depending on who
pulls it. Pulling it yourself may be a bit of a pain but it has its
advantages. It 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. You can use part of the original Volvo
bracket, and make your own adjustable mounts out of 1/4" steel plate.
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,
www.onboardair.com also has a
serpentine/v-belt combination pulley for alternators that will allow you
to run a v-belt to the compressor.
York Compressor Mounted
Keeping the 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, you'll have to come up with a
dipstick. You can make your own out of a coat hanger, or buy one from
www.onboardair.com. Make sure
all of the old oil is drained from the compressor before you hook it up.
This will require removing the head, and letting it sit upside down for
a few hours.
After cleaning it out, fill the compressor with 10W-30
motor oil and start hooking up the switch and air lines.
Air tank: The next step is to find and install an
air tank somewhere on your rig. 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. If
you have a semi/large truck salvage yard nearby you may be able to save
some cash by using an air tank from an old air brake system. Be sure the
tank is rated for 150 psi and has several 3/8" NPT ports. Put a 140 psi.
pop-off valve in the tank and plug the holes not used. The tank can be
bolted to the underside of your rig near the rear driveshaft if there's
Pressure switch and air fittings: To complete the
system, you'll need 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. You can also
install a master on/off switch inside your rig to control power to the
pressure switch. The pressure switch is a SquareD model #FHG12J52X. It
comes with or without an unloader. The unloader relieves the pressure on
the pump when it stops, allowing it to start back up a little easier.
Here's a link to the catalog on the SquareD website for their pressure
The flange fittings for the intake and output ports on
the York came from
www.onboardair.com. Their fittings make setting up the air hoses
much easier because the threads are a standard size, and most of the
fittings you'll need can be found at a local hardware store. For the
intake filter, use an exhaust muffler from Grainger (part #1A328). It's
compact and mounts directly to the flange fitting. For the output side,
use 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.
Install the pressure switch, and hook 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. Run a line from the "T" to
the tank. Then run a line to the back of your rig with another
quick-disconnect. You'll really enjoy having air at both ends of your
Hand throttle: while it's not absolutely
necessary, installing a hand throttle to get the engine RPM a little
higher when the compressor's running helps speed things along.
Parts used and part numbers:
SquareD pressure switch #: FHG12J52X (125 psi max w/30 psi differential,
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