York OBA for a Small Block Chevy

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 space.

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 switches: click here.

Compressor Fittings

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 rig.

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, and unloader)

www.onboardair.com: Flange fittings for York 1/2" NPT www.onboardair.com

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 www.grainger.com



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