Interior Heat Control Mal-functioning

On my 1999 Expedition, I continually receive heated air from the dashboard vents, even with the air blend knob (temperature knob) turned to cool.

The truck also has a rear heater/air-conditioning console. The above problem is not occurring with the rear console, only at the dashboard vents.

I would appreciate any advice as to the problem with the air heating system. Thank you.

All of the mixture vents in the dash are controlled by vacuum. The some of the small vacuum hoses along the firewall near the battery are the control hoses for the vents under the dash. These hoses and hard plastic connectors will deteriorate with age and battery acid so close. My suggestion is to check these for leaks/breaks and repair if so. This is identical to what happened on my 98 Exp and cured the problem.