On-Board Air Compressor
Page 2
Selection of an air compressor
There are basically two different types of compressors used for on-board air. One is the York and the other Sanden (Sankyo). Both compressors are of a piston design. The York has a piston with a connecting rod much like an engine, the Sanden usually has 5 to 7 double ended pistons that are actuated with a swashplate or wobble plate on the center of the drive shaft.
There are some pros and cons to both types but they both will work.
The York compressors tend to be physically bigger than the Sanden and therefore a little harder to mount in an already crowded engine compartment and they tend to be really heavy. The York compressors are internally oiled which helps keep them running. However, it is hard to find a York in the wrecking yard with a stock serpentine pulley arrangement and due to their size the York can be hard to fit into a TJ without some modifications to your inner fender wells, etc. The York compressors do tend to put out more air than the Sanden compressors though.
Sanden compressors are much smaller and more compact. They come in several different mounting configurations one of which is the type used in most of the early TJs that use 4 bolts passed through bolt tunnels on each corner of the compressor and attach to a plate that the compressor sits on. The other type had 8 "ears" 4 at rear and 4 at the front and the bolts insert parallel to the compressor to attach it to mounting bosses on the side of the engine. Both types will fit but we tend to prefer the latter with the "ears" as they tend to be a little bigger, air up much faster and are easier to fabricate mounts for.
Stock compressors from most Jeep Cherokees work really well and usually have the correct serpentine pulley on them. Sanden compressors have an oil fill plug on the top which is used to add oil directly to the compressor. Several sites on the net refer to making a dipstick to check the oil level in the Sanden type of compressors but believe me, don't waste your time, it isn't necessary. This is because there never is a measurable "level" of oil in these compressors. They were meant to be lubricated by the oil in the closed system since it is always circulating. It is advisable to periodically inject a little oil directly into the fill plug but if you forget it really isn't much of an issue since most of our compressors have been running for over 5 years now without having done this.
Tips for finding the right compressor:
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Take a 12 volt battery and some test clips with you to test the clutch (a motorcycle battery works well). If the compressor has two wires then place one on the positive and one on the negative terminals of the battery. Turn the pulley and see that it turns the compressor. If the compressor you choose has only one wire, then place it on the positive side of the battery, connect the negative post of the battery with a test clip to the side of the case of the compressor.
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Hold your finger over the high pressure side of the compressor (should be the smaller of the two hoses) and turn the compressor, it should get hard to turn after just a few rotations as the pressure builds, remove your finger and listen to make sure you get a good puff of air. I have found that some compressors will not make much air by just turning them by hand, so you can have an assistant take a serpentine belt and use it to turn the compressor faster by using a sawing motion with the belt around the pulley. Make sure you have a 12v battery connected to the clutch to engage it or the compressor will not turn.
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Pay close attention to the pulley! Even on the same model year of car I have seen them use 4, 5 and 6 groove pulleys. For installation in the Jeep you need a 6 groove pulley.
On-Board Air System Installation
Following is a diagram of how the different components in the OBA system should be connected. Actual Mounting locations will vary depending on the vehicle. Click for larger view.
Removing the stock air box
In preparation for installing a second air conditioning compressor to be used as an air compressor on the earlier TJs it is necessary to remove the stock air box. This is actually a really simple operation. With a hacksaw cut the air tube just behind the existing air conditioning compressor over the engine. The stock air box can then be removed.
You can then install a K & N air filter number RU-0960 available from many outlets online. Slip the new filter over the end of the air tube and tighten in place with the supplied hose clamp.
Intake noise is increased a bit with initial engine start up, but it does subside when the engine warms up. As you can see from the pictures, removing the air box frees up a lot of room for a second compressor to be mounted next to the air conditioning compressor.
The air compressor master switch was installed just forward of the 4x4 lever in the center console. We like to use a stock ARB compressor switch, which has a small light that is wired to your dash lights and a larger light that illuminates when the switch is turned on. Other switches are also available online with a compressor symbol on them.
Compressor Install
Installation of your compressor may vary due to the type of compressor you choose and the model year of your Jeep. Later TJs can be a bit tougher as the different engine accessories are located in different places around the engine than the earlier TJs. Each vehicle and engine design presents a different challenge in mounting a compressor. The main thing to keep in mind is that the belt must come in contact with at least 1/4 of the circumference of the pulley and the compressor has to be mounted so that the belt runs smoothly around the pulley (cannot be out of alignment with the path of the belt in any way) We have had to relocate alternators or other components on the later (2004 on) TJs in order to install a compressor.