Air Conditioner from engine

The Valve,you mentioned, is called an Air Dam or Air door. is likely operated by ending vacuum and a vacuum motor.

If there is no vacuum the system defaults to DEFROST so check for air out the defrost vents.

Causes of no vacuum and I've see all these over 50 years of cars

Broken vacuum hose
Hose off fitting
Connector off valve
And the one that really got me was a cruse control solenoid (Also a vacuum device) which got religion.. Yup. it was HOLEy.

The Dash AC system is NOT Ford. So, Ford cannot help you. The compressor IS Ford. The system should be Evans Tempcon. Click on this link and follow to the troubleshooting guide. Output to the various ducts is Vacumm controlled by the Ford engine. Odds are the Vacumm hose is old and leaking or fell off. Doug

https://proairllc.com/design-engineering/evans-tempcon-guides/

Thanks for the analysis. I'll check out hose leak and move on from there.

diverter door or its control module.

As above, vacuum drives the air controls, but with some models, loss of refrigerant can also cause the default to defrost.

A bad compressor or clutch as well as a holed line or evaporator would all be suspects.
Can you see the compressor? Is the clutch engaging? If so, have you tried adding a can of refrigerant?

Offhad I suspect a vacuum system problem; if memory serves, the controls for the heater and air conditioner are vacuum actuated on the chassis. I'd hunt for a bad hose or a cracked or otherwise compromised accumulator for the HVAC controls. It may well be buried someplace not too accessible behind the dashboard.

All the doors that direct the air flow run by vacuum and default to defrost when vacuum is lost.