I'm working on a R134 retrofit.

That compressor has more steel and bolts holding it onto the engine than what they used to mount the engine into the truck. After much cussing and sweating I finally got it off so I could drain it.

I ended up having to remove my oil filter and slide the compressor back so i could take the lines off and then drop the compressor out of the bottom. Of course this was after I removed about 8 really tight, over kill sized bolts. I'm not looking forward to putting it back this way because getting the lines back on is really going to be a PITA.

So how should I have taken it off?

 

According to fsm...
remove belt
discharge system
remove lines
cap lines
remove 2 capscrews that connect to water inlet bracket, in front
remove 2 capscrews from bracket in back
spin compressor and remove
all done from below

sounds like you removed the brackets from the block...Mark

 

Well, there's really two brackets. I took the one that the back of the compressor mounts to off. Other than that, I pretty much did what they said.

Its a better man than me that can unbolt those AC lines from the bottom side, and doing it from the top is pretty hard unless you pull the oil filter.
Surely Chrysler wouldn't have understated the proceedure

 

I added the from below part and wasn't thinking about the lines at the time...My bad ...Mark

 

I remember 4 really long 1/4 or 5/16 bolts that broke when I took mine out. I had to drill a hole in the compressor thru the bolt so I could get it off. I was replacing it anyhow. Really tucked in the frame rail and the bolts had to go in before you put it up there as I recall.

 

The non i/c compressor is definitely mounted oddly! Much like the way you removed yours, I remember fighting with mine for a little while. Luckily I was doing all this while replacing a head gasket so my oil filter and other parts weren't in the way. I don't understand why that design when a year later, in the i/c models, they changed to a 4-bolt, square pattern. Compared to mine, the i/c compressor would be a breeze to remove!

 

I swapped my 89 motor over to the IC style, Sanden A/C compressor. Simple and cheap. I couldn't find a C171 Diesel compressor anywhere, and if I had it would have cost me about $5-600!! I got the engine bracket, new Sanden A/C compressor all for under $200. You will need to run new A/C lines though if you go this route.

Here's what I did....

https://www.dieseltruckresource.com/...c-t289065.html

 

I believe that the Cummins is all metric which would mean those are metric bolts.
I have found that 5/16 will screw on to that particular size with the results you mention. (8mm i think)
The threads will be off just enough to make them tight.