[A/S] Armstrong A/C Model 21-12

[Robert Gill <bobbyg31605@xxxxxxxxx>]

Hello. I'm having trouble with my A/C unit and would
like to get something done with it before it gets hot
down here in South Georgia. I think the run capacitor
is bad, but I can't find it. The label on the fan
motor states it has a 7.5 MFD capacitor. Even the
wiring diagram shows another capacitor. But I have yet
to find it, after looking everywhere on it, I'm about
ready to just R2 the whole A/C. The capacitor cost
$2.66, a new A/C cost $500.00 and up, but has a three
year warranty, the Armstrong is obsolete. The only
parts that I can find to replace are capacitor, wire,
fan blade, freon, so if anything else were to go out,
I be left with no choice but to R2 the A/c.
Anyone have A/C unit they recommend? Also someone in
South Georgia (Valdosta) area that works on Airstreams
that could do this? 
My local RV guy said he'd charge $25.00 to
remove/replace A/C unit, so at that price it makes me
think it's a fairly simple job. Anyone tackeled
changing A/C unit? How hard? 4 bolts and some wiring?
Any info is welcomed.
Thanks
Bobby
'73 Ambassador