air conditioning not working right

[ncsparky1]

I haave a 2004 Chevy 2500 express van that is blowing out hot air sometime and sometime cold air. I have had the freon checked and it is ok. The fan motor was going down to nothing when going up a hill or under heavy acceleration. I replaced the vacuum hose from the manifold to the vacuum reservoir cannister and also replaced the vacuum check valve. Seemed to help a little, but still have the same problem. It seems that it don't need the acceleration now to "not work". When it does work, it blows out ice cold air.
I've seen videos of using a "smoker" to find a vacuum leak. I guess this is my next step. Thinking about purchasing one or just taking it to a mechanic that already has one. I understand there are "shutters" inside the dash, etc. that may not be opening. Can anyone give me some more input before I take it to a garage. I'm hesitant on taking it unless I know they are experienced in this type of problem, knowing it will take them possibly longer to diagnose the problem $$$ Thanks for any help you can give me.

[Blue Bowtie]

Try to find vacuum hose routing diagram for the van. I know that some GM vans used a vacuum reservoir (Dorman 47083) mounted on the RH frame rail just ahead of the firewall, in the RF corner. The hose connection on those can break, and/or the ball can crack, causing the symptoms you describe.