69 Heater Control Valve

Working on a non-A/C 69 with a 390. The service manual shows a heater control valve on the lower heater hose. There also appears to be a vacuum hose going to this valve. The upper dash is off and I cannot find a place on the heater controls or heater box that would have a vacuum switch. Is there supposed to be one?..if not I will add one. Would really like to turn off coolant flow through the heater core when heat isn’t needed.


Both the A/C and “Comfort Stream” / “Power Vent” ( power ventilation ) systems used a valve to restrict the flow of hot coolant to the core in the HVAC box under the passenger side dash. The valve was service p/n C7ZZ-18495-A ( YG-98 ) r/b D1AZ-18495-B ( YG-110 ). If your '69 Cougar was not equipped with either options you could add a valve to the hot coolant ( inlet ) hose on your car - look in the service manuals for the location. You would have to obtain a vacuum source for the valve and a switch to activate the blower motor and allow vacuum to close the coolant valve at the same time. Would probably be easier to find the “Comfort Stream” system in a donor Mustang or Cougar and install it on you car, that way you would get the vacuum hoses, coolant valve, proper dash controls, vacuum switch on the heater box and the correct blower motor ( which has a by-pass hose for cooling the motor while the power ventilation is in operation ).
The switch you are referring to / looking for is p/n C6OZ-18C311-A:

and it is available from WCCC ( item # 26094 for $ 9.57 ) It would probably mount in the same location on the Heater box as an A/C equipped vehicle, and would be controlled by the temperature setting ( sliding ) control cable. But without all the other hoses as found in an A/C car, I’m not sure where the vacuum would be sourced from in the Power Vent system. Again you’d need to look in the Service manuals for the vacuum schematic for that application.

Here’s a link to WCCC ( West Coast Classic Cougar ) to help you identify all the components required ( they don’t appear to have one in stock at this time ):

Here’s a link from Concours Mustang discussing ( the pros and cons of ) this feature :

Also here is a description of the option from the July 01, 2005 Motor Trend Magazine:

“The Power Vent System was a $40.02 stand-alone option that was available in lieu of air conditioning. It was a center register added to the basic standard heater system. The dash control had a position marked “Power Vent” in small letters just to the right of the defrost position. When the control lever is switched to Power Vent, a vacuum control duct opens above the radio and can be directed by setting the blower speed. Cool and hot air can be blended to achieve the desired temperature with the same temperature-control knob the heater utilizes. The Power Vent option wasn’t very popular, thus it’s rarely seen on Mustangs today. I believe most new Mustang buyers were simply not aware of this option, as salesmen pushed air conditioning to raise their commissions. It really works well and it’s nice to have outside air coming out of a higher center register instead of the lower kick-panel vents only. The 1969 owner’s manual illustrates the controls and operation in the Comfort and Convenience Features section.”

This description / image is from https://media.ford.com/content/dam/fordmedia

Screenshot 2023-05-18 at 11-03-50 1969 Mustang data - 1969_Mustang_Data.pdf
Screenshot 2023-05-18 at 11-04-10 1969 Mustang data - 1969_Mustang_Data.pdf

Or you could install one of these and a cable to turn off the hot water in the summer:

Manual Heater Control Valve