[alex21278]

Hi all,
Im new in this, only 21 years old and working on a 1965 Pontiac Star Chief, 389 V8, 2-bb with AC and I’m trying to confirm the factory vacuum routing on A/C cars. I read 1965 Pontiac shop manuals and read forums but still wanna get confirmation.


My understanding:

Non A/C cars: rear vacuum tree block on carburetor with 3 connectors
Right → brake booster
Middle → TH400 transmission modulator
Left → distributor vacuum advance

A/C (my car):
Right → brake booster
Middle → TH400 transmission modulator
Left → through firewall to HVAC (with check valve). Instead distributor takes ported vacuum from the front of the carb and is connected with a steal pipe.

Can A/C owners of ’65 big Pontiacs (Star Chief/Bonneville/Catalina/GP) confirm this and share any photos/diagrams? If you’ve swapped to 4-bbl, did you keep the same logic (tree→HVAC, carb front→distributor)?

Pics of my setup attached.