Climate control "flakey"

Ok, heres the deal. Took my 95 conti to an ac shop.
They put some freon in ( just had engine replaced)
Told me the evap and comp were leaking bad and all in all
an $1100 job was pending. It did cool though to a degree.
I do some ac myself so I hooked up and found low charge.
I brought the level to spec and in last 6 weeks the ac has
been anything from ice cold to blowing hot air and it kinda
depends on the "mood" the car is in. I have been told that
the vacuum system is very critical to the operation and that
even a partialy pluged cat conv or a bad tune up can cause
vac levels that would make the system not control the vac
motors that change air mix, and therefore cause the very
unpredictable operation. 6 weeks later I still have Ice cold air
when I get it, so phooey on the freon circuit probs the ac
shop claimed. My question , I do have 2 bad O2 sensors,
possibly some clogging in the cat converter, and tune is not
perfect. Very drivable though and performance is "decent",
even if not perfect. Is the vac really that critical to the
climate cont system that just a tune or cat could fix that
problem ? I have a vac and electrical sys factory manual on
its way to me to help locate parts and troubleshoot also.
T I A for any advice or any experiences anyone can share. Phrawg

I'm not exactly sure how the Vac System would affect the A/C but then again, I'm not familiar on newer model A/C systems. I own and drive daily a 1980 Mark VI and the way my A/C is powered is by belt which turns a clutch which actuates the compressor. As far as I know, the A/C [on my car] is completely independant of any other system aside from using the vents inside the car. First of all, get rid of the Cats. They hog horsepower and precious fuel mileage, so if it's even possible due to the computer, take them out, especially if they are clogged because that will just back things up even more. You're car will sound a little louder but that can be counteracted with a muffler, if you're not into a loud sounding car. The Cat's are mostly for exhaust purposes and emitions and I'm not sure how they'd affect your A/C. It would seem, from my perspective, that the shop was snowin ya, to put it lightly. It's possible your O2 sensor is causing a problem. I know my parents 2003 Expedition had something go wrong and my dad figured out after months of research that it was the O2, totally didn't think that was the problem. All else fails, see about getting a new compressor or a refurb would be more cost effective. I hope I've got all your questions answered.

I'm not exactly sure how the Vac System would affect the A/C but then again, I'm not familiar on newer model A/C systems.

I'll revise that....the Vac System is COMPLETELY UNRELATED to the operation of the A/C system on any year or make or model. The only relation, apparently, is the "ON/OFF" control or something.

if you look on the back of the climate control there are vacum tubes that due effect the way it works which i do not understand it's not in my haynes manual. however i have the same problem, tried replacing with one from junkyard same problems. so now what, thats the million dollar question there are i think 6 or 7 ports on the back for vacum hook up and two harnesses which prob direct the air somehow, this is just a guess i have no clue

I am having problems with the gates with in the climate control system which is not allowing me to get heat. MY machanic say that in ordre to correct the problem I would have to order the whole climate control unit which cost $1000.00. My question is can the gates be order separate and would it cause ano heat problem.