Figured i'd document this and do as good a job as i can stomach in terms of a detailed write up. There are many ways to skin a cat, this is but one. I went this route because i thought it was quite cool, i like the idea of repurposing things, wanted to keep my electrical system cleaner and its been known to have the 7 piston SD models putting out up to 8-9cfm by my research. It runs quieter and can serve up a massive amount of air. By comparison, a very expensive 12 volt system can't match the CFM rating. The install is also cleaner for the most part, hugging the engine and leaving lots of peripheral space for other fun doo-dads. Seeing as how i know i will be stuck with the 4 squirrels for at least a little while yet, i figured it was worth it.
I got a hook up on two Sanden OBA compressors from a mid-late 90s Cherokee - best part was they were free and fairly clean looking from the outside. They aren't the IDEAL Sanden model to use (These are model #4691 - AFT SD-709T).
YJ Sanden A/C Compressors makes this a bit of an easier job in terms of hooking it all up. The main difference would be the cylinder head of the units. YJ's SD 709s have rear ports on the unit and they are threaded externally. My models utilize vertical ports at the top of the head with a manifold.
I ran over it back and forth which way to go about using this - you can repurpose/use the manifold in a number of ways, i chose to cut threads in the ports at 1/4 NPT - 18 and directly hook up the input and output lines directly with teflon tape. A good back up plan that i ran over with many /f12 members back and forth would be to utilize weld bugs and braze them into the ports off the valve cover directly - bypassing the manifold entirely.
First thing you're going to want to do to get the ball rolling is remove the 6 bolts at the backside of the unit holding the head onto the unit with a 13mm Socket. The head may be a little stuck on. There are two 'divots' along the edge between the cylinder head cover, it's gasket and the unit itself. You can pry it off with careful work with flathead. *BE CAREFUL. Try your best not to damage the head gasket*. Once you have cracked that, stand the unit on its pulley and pull the valve cover off. Doing this, gravity should keep any oil still within the unit in place and not making a mess (I did this in my condo lol).
Get some brake cleaner, rags and start cleaning everything up. You can separate the gaskets from the valve plate after removing the 10mm bolt and nut which keeps the valve plate assembly together. There is a gasket on either side of the plate - you can replace these if there looks like there was any corrosion on any of the internal components and the plate itself. Everything looked a little dirty, but in real good shape after a quick clean up. I was also lucky to not have any struggles removing the gaskets from the valve plate. I simply cleaned it up with layers of brake cleaner, and a light scuffing on a low speed with a wire brush at an angle in my drill. Worked out well for me.
Because your hands are kind of full for the pulley removal, it was difficult to take pictures of disassembling the front end of the unit. Your gonna need snap ring pliers, refer to photo below from the SD series manual.
I should note that the only special tools i had during the removal and re-install were snap ring pliers. I got by with ingenuity for most of the special tools displayed up there in those images. But, if you want, see below:
Once you the pulley and field coil assembly out of the way, loosen the 8 bolts holding the facia onto the front of the unit with a 10mm socket. The facia will begin pushing up as you backout the bolts on its own. It's normal, don't worry. There isn't much pressure so no worries about your safety here. Just undo those bolts and then pull straight up and Voila!
From here you grab the internal workings and try to pull straight up as a unit, you can help yourself out immensely by also pushing/guiding the piston assembly up from the bottom by the piston heads. Once that is out, give everything a nice cleaning with brake and parts cleaner and wipe it all down well. Analyze the walls and all the components closely for any gouges, scrapes, chips, warpage, damage of any kind. My unit was kick *** spotless, i cleaned up the oil residue and was good to go!
Next step is to grease everything up nicely if you're going the route i did. If not, and you will be running an inline oiler, clean up and lightly oil everything and re-assemble. I used high-heat bearing grease and slathered it everywhere as i wanted to keep it as easily maintained as possible going forward and didnt like the idea of a cheap chinese oiler or something from home cheap-o i would have to keep an eye on. A few squirts of grease out of a gun every couple months (based on usage of course) sounded like an easier and better option. The oil fill plug of my Sandn unit would be on the engine side of the compressor which is not ideal to get to so i went with a 90 degree elbow grease zerk fitting. This was used to replace the unit's oil fill plug. I retained the rubber O-ring and lock-tighted sealed the fitting in place. I got it to point as close to vertical as possible to make for easy greasing down the line.
You're now ready to make sure you clean the mating surfaces really really well, especially in the groove.Make sure you line up the large o-Ring/gasket in its place where my finger is pointing below:
Now guide the piston assembly making sure the race and thin bearing which sits on it are properly placed and greased. It will take a little finagling, again utilizing the open cylinders from the bottom side to manipulate the pistons as required to get it all to slide in helps a lot! Once you have it all lined up, press it down and in place fully until it is seated on the ball. Below reveals how much clearance there should be when fully pushed down. It will take its angle as you tighten down the bolts on the facia/cover.
Tighten those 8 bolts down to ~25-28 Nm with lock tight.
Before we get the valve plate re-installed, i drilled out the weep hole circled in the first pic below and tape 1/4" x 1/4-20 and lock tighted in a grub screw (low profile). This will minimize any grease getting through and out of the compressor.
Now we're ready to put the gasket components and butterfly valves back onto the valve plate, bolt it together and stick it back onto the @$$ of that compressor and torque everything back down.
Refer to the manual instructions posted earlier up there ^, reverse everything and reinstall the field coil, snap ring, pulley wheel clutch assembly, snap ring, the shims that came on it, the facia and 14mm bolt. lock tight and torque down. Make sure the wheel spins freely with no grinding sounds and you have your compressor back together! We can now move onto the real fun stuff.
Here we have the shims pictured:
I got a hook up on two Sanden OBA compressors from a mid-late 90s Cherokee - best part was they were free and fairly clean looking from the outside. They aren't the IDEAL Sanden model to use (These are model #4691 - AFT SD-709T).

YJ Sanden A/C Compressors makes this a bit of an easier job in terms of hooking it all up. The main difference would be the cylinder head of the units. YJ's SD 709s have rear ports on the unit and they are threaded externally. My models utilize vertical ports at the top of the head with a manifold.


I ran over it back and forth which way to go about using this - you can repurpose/use the manifold in a number of ways, i chose to cut threads in the ports at 1/4 NPT - 18 and directly hook up the input and output lines directly with teflon tape. A good back up plan that i ran over with many /f12 members back and forth would be to utilize weld bugs and braze them into the ports off the valve cover directly - bypassing the manifold entirely.
First thing you're going to want to do to get the ball rolling is remove the 6 bolts at the backside of the unit holding the head onto the unit with a 13mm Socket. The head may be a little stuck on. There are two 'divots' along the edge between the cylinder head cover, it's gasket and the unit itself. You can pry it off with careful work with flathead. *BE CAREFUL. Try your best not to damage the head gasket*. Once you have cracked that, stand the unit on its pulley and pull the valve cover off. Doing this, gravity should keep any oil still within the unit in place and not making a mess (I did this in my condo lol).


Get some brake cleaner, rags and start cleaning everything up. You can separate the gaskets from the valve plate after removing the 10mm bolt and nut which keeps the valve plate assembly together. There is a gasket on either side of the plate - you can replace these if there looks like there was any corrosion on any of the internal components and the plate itself. Everything looked a little dirty, but in real good shape after a quick clean up. I was also lucky to not have any struggles removing the gaskets from the valve plate. I simply cleaned it up with layers of brake cleaner, and a light scuffing on a low speed with a wire brush at an angle in my drill. Worked out well for me.


Because your hands are kind of full for the pulley removal, it was difficult to take pictures of disassembling the front end of the unit. Your gonna need snap ring pliers, refer to photo below from the SD series manual.






I should note that the only special tools i had during the removal and re-install were snap ring pliers. I got by with ingenuity for most of the special tools displayed up there in those images. But, if you want, see below:

Once you the pulley and field coil assembly out of the way, loosen the 8 bolts holding the facia onto the front of the unit with a 10mm socket. The facia will begin pushing up as you backout the bolts on its own. It's normal, don't worry. There isn't much pressure so no worries about your safety here. Just undo those bolts and then pull straight up and Voila!


From here you grab the internal workings and try to pull straight up as a unit, you can help yourself out immensely by also pushing/guiding the piston assembly up from the bottom by the piston heads. Once that is out, give everything a nice cleaning with brake and parts cleaner and wipe it all down well. Analyze the walls and all the components closely for any gouges, scrapes, chips, warpage, damage of any kind. My unit was kick *** spotless, i cleaned up the oil residue and was good to go!


Next step is to grease everything up nicely if you're going the route i did. If not, and you will be running an inline oiler, clean up and lightly oil everything and re-assemble. I used high-heat bearing grease and slathered it everywhere as i wanted to keep it as easily maintained as possible going forward and didnt like the idea of a cheap chinese oiler or something from home cheap-o i would have to keep an eye on. A few squirts of grease out of a gun every couple months (based on usage of course) sounded like an easier and better option. The oil fill plug of my Sandn unit would be on the engine side of the compressor which is not ideal to get to so i went with a 90 degree elbow grease zerk fitting. This was used to replace the unit's oil fill plug. I retained the rubber O-ring and lock-tighted sealed the fitting in place. I got it to point as close to vertical as possible to make for easy greasing down the line.




You're now ready to make sure you clean the mating surfaces really really well, especially in the groove.Make sure you line up the large o-Ring/gasket in its place where my finger is pointing below:

Now guide the piston assembly making sure the race and thin bearing which sits on it are properly placed and greased. It will take a little finagling, again utilizing the open cylinders from the bottom side to manipulate the pistons as required to get it all to slide in helps a lot! Once you have it all lined up, press it down and in place fully until it is seated on the ball. Below reveals how much clearance there should be when fully pushed down. It will take its angle as you tighten down the bolts on the facia/cover.

Tighten those 8 bolts down to ~25-28 Nm with lock tight.

Before we get the valve plate re-installed, i drilled out the weep hole circled in the first pic below and tape 1/4" x 1/4-20 and lock tighted in a grub screw (low profile). This will minimize any grease getting through and out of the compressor.


Now we're ready to put the gasket components and butterfly valves back onto the valve plate, bolt it together and stick it back onto the @$$ of that compressor and torque everything back down.

Refer to the manual instructions posted earlier up there ^, reverse everything and reinstall the field coil, snap ring, pulley wheel clutch assembly, snap ring, the shims that came on it, the facia and 14mm bolt. lock tight and torque down. Make sure the wheel spins freely with no grinding sounds and you have your compressor back together! We can now move onto the real fun stuff.
Here we have the shims pictured:

