Electronic Hater/A/C Controls Blows out Defrost Ducts - Frod, Lincoln, Mercury

A poorly fitting vacuum harness to the control head results in vacuum leaking and air blows out the defrost ducts by default by law.

You can replace the vacuum harness or use two 10" tie straps that wrap around the back plate and go on either side of the black vacuum supply hose. I have photos I can send out if needed.
The vacuum harness is $22, but even if you replace it, you should use the tie straps. There is not enough of an interference fit bweteen the hoses and the tubes.

You also may have internal vacuum leaks on the control head back/bottom plate. It has 4 solenoids that direct vacuum to the correct vacuum motor on the plenum. Thy have been known to leak.

Gino on Ebay fixes them on an exchange basis for about $125.