Of course I lost the low side service cap. Went to O'Reilly, the normal stocking item does not fit. We looked up the accumulator and the cap that came with that was correct, but we couldn't deduce a part number.
went to the zone and tried everything he had in as well. They ordered six other caps so that we can try them tomorrow.
Seems that standard caps have an 8mm thread, and mine is just a bit larger, but not 10mm as the high side caps are (that we tried).
I searched the forum and didn't find any complaints about this, does anyone know what I have going on here?
​​​​​​ Vehicle is a 99 F250 2wd 5.4 single cab

 

Go to the junk yard and get one.

 

Is the accumulator OEM or aftermarket? If the latter, it's going to be pot luck as to what that manufacturer installed.

 

I'm not sure of my accumulators origin.

But AutoZone found one that fit, the part info is as follows.

Santech MT0061
Comes in a baggy of 5 for less than 3 dollars.
The spec page on their PC says it is 9mmX1 thread.

So now I have four of them left. I'd be willing to share if we can find a shipping solution lol