A/C Vacume question

I have a 2000 Ford Ranger 2.5L engine that I just replaced the A/C Compressor, Dryer, and venturi tube/filter, vacumed the system and recharged the system. It is working fine however the blend door is not operating properly and the cold air only comes out the defrost vents, I have narrowed the problem down to a vacume problem, this system uses vacume tubes to change the direction vents and open the blend door and there is zero vacume… My question is… how can I pinpoint where the vacume problem is?

Check to make sure you didn’t unknowingly disconnect any vacuum hoses when you did this repair. The vent control has a vacuum line from the engine, thru a check valve, into vacuum reserve canister, and thru the firewall to the vent control panel.