A/C refrigerant amount

I have a 1998 379 peterbilt w/an ultra sleeper. It has a condisor that is 28"×28" (pretty large), and bunk a/c is ran off same compressor system as cab. Compressor came with full oil charge, but no one and nothing as the amount of 134a freon. Looked at fire wall, compressor, accumulator, and under bunk will replacing, cleaning, and flushing entire system with acetone. Nothing.
Called verious rush peterbilt dealers and have nothing on this unit.
Does anyone here have a truck with a sleeper and has a 28"×28" sleeper,close to 1998 that has a sticker with amount? Or someone with paperwork stating the amount of 134a?
Thanx. I'd like to do it right

 

Last 6 of vin # is 455445 if it helps

 

She's been on vacuum for 5 hrs. Down to about 29-29.25. Got gauges but past experience 134a really picky about being to low or high. Even a little.

 

No sight glass on system

 

Any chance your condenser also 28"×28"?
And I've checked the cowl too. Had another Truck that was there, but not many know about it. Thank you.