The vacuum-operated heat and A/C control in my ‘68 doesn’t work. The vacuum source is being taken from the base of the carb and feeds directly to the control without benefit of a vacuum canister. This doesn’t seem right. I’ve looked high and low in the service manual but haven’t been able to find reference to verify the correct vacuum line source, or confirm there should be a canister. I’m sure the source should be ok, but what about a canister? I checked for vacuum leaks downstream of the carb with a gauge and the system seems to be pretty solid (very small drop, a minute or so to lose all vacuum). So my follow-up question is this: at idle should the control work without a canister, or do I have a deeper problem? There are no vacuum sounds when the control is moved between settings. Thanks!