Thats usually caused by the one way check valve on the BBM solenoid dying and becoming a 2 way valve.



Not many options. It's Fords way of saying "f**k you" to the repairing public, the screws that hold the heater box together face the firewall. So the box has to come out.

I've read of cars where the rod that the flap swivells on breaks away where it passes through the heaterbox outer wall. You might be lucky enough to remove the blend door motor and find something broken right there that you can glue back together. Either way, still is a dash out job.



Tell her to put another coat on and harden up!

nah was just a split hose coming off the manifold fitting as i said, when i accellerated it opened up and i would lose vac to the module.

the only reason i mentioned it was because his only switches to cold when accelerating or braking hard, so it may just be a hose.
the control module on the heater box needs vacuum to work and it cant electronically switch the blend door motor if theres no or not enough vacuum .

im sure EFFalcon will work out the problem

Still sounds strange. They have a vacuum canister to store vacuum for the system. The one way valves are to prevent it leaking back out to the atmosphere. Even after you switch the car off, you should be able to change air direction 3 or 4 times with the stored vacuum.



Air direction on climate systems is controlled by vacuum, but not heat levels. Thats controlled entirely by an electric blend motor.

The heater tap is controlled by vacuum, but its default state is open, allowing water to flow into the heater core. It needs vacuum applied to it to stop water flowing for cool air. So if it is a vacuum problem, technically he'd always get hot air when he didnt want it.



And I wish him luck.

I appreciate your input, but yeah.. its more the inertia moving the flap under accel/braking suggesting the flap isnt connected to anything.

ok if its inertia, disconnect the vacuum line off the manifold and block the barb on the manifold fitting. then take the car for a test drive and see if it is still moving and making the noise

Can you hear the slight thud the blend door makes near the end of a calibration ??