Hello All Fellow Olds Enthusiast. I Changed the Intake on My 1970 F85 to a 4 Barrell Intake. The AC and Heater both Worked Fine before The Change. I now do not have Heat but the AC works. I can hear the Ducting changing so that is not the problem. I have narrowed down the problem to the vacuum Pot On the Dash Control not Sending Vacuum to the Intake Valve that sends Hot Water From the Intake to the Heater Core. I have pulled the line off under the Dash and put Vacuum to it and the Heat comes on. There is also Vacuum coming into the Dash Control, It just does not direct vacuum to the intake when switch to Heat from the dash control. I believe all the vacuum lines are connected correctly. I hope someone might know where i can go from here. Thanks for your Help.

 

My 73 Omega doesn't have a valve in hot water line at all. On/off done by ducting baffles.

Unless previous owner removed the valve ???

 

The system will have a coolant valve only if equipped with A/C.
Is the coolant valve your original or was it changed when you swapped the manifold?
If the same, sounds like one of the vacuum switches on the control panel is non-functional.
If a different valve, it may be operating oppositely then it is supposed to.

BTW, welcome to the forum to both of you!

 

The valve on the intake SHOULD be normally open. Vacuum is only applied at the MAX A/C position to close the valve. This is unlikely to be your problem. More likely is that you have the vacuum hoses connected incorrectly to the actuators on the HVAC box.

When the engine is at operating temperature, touch the two heater hoses to see if they are hot. If not, it's possible that the heater valve on the intake is stuck closed or the heater core is plugged with some rust or other debris. If the hoses are hot, the problem is elsewhere.