need to know on a 73' A/C 250 car where the ...heater control valve gets its vac. thanks for any help...
It will be a vacuum hose coming thru the big black plug on the firewall. The other hose thru that firewall plug goes to the vacuum canister.
...... Jeff showed me a digram last night (thanks Jeff) that has a brown hose to the valve, it said "partial vac.". would you know if that's full vac. at startup and drops it when turning the heat on. I found a heater valve that with full vac. the valve is closed and the water loops back to the block. when vac. is dropped it opens and water goes to the heatercore.
I really don't know the ins and outs of these valves and the vacuum system. I just hook up the colored coded vacuum hoses where they go and it works.
There is a vacuum reservoir (black coffee-can-shaped thing under the fuel carbon canister, next to the starter). This device and it's check-valve ensure the climate control has vacuum when the engine is producing little vacuum, such as under acceleration. If yours is original, it's likely gone bad. I'll send you the test procedure for the vacuum reservoir, if you wish.