Mercury 2004 Grand Marquis blend door failure

This vehicle does NOT use a heater control valve. Coolant flows to the heater core at all times. Temperature is regulated by the blend air door and blend door actuator. Locate the blend door. Remove the actuator and open the door by hand. If you get heat, the actuator or the control head is bad. FWIW, the actuator is the most likely cause

Look At It When Moving Controls--You Should See It Move. NOTE: If Blend Door Itself Is Seized Due To Case Problem It Will Damage Actuator (not a uncommon problem)

thats a big job you have to remove the steering colum and the dash and the black box to to get to the blend check out ford forums for shortcuts

should be on passenger side behing glove box. if your taking about the blend door actuator it should be attatched to door or door beam with cable running behind glovebox to the heater control

Sounds like ??
If the compressor is running and the system is full of freon, you may have a blend door problem under the dash. The blend door directs air flow thru the heater core and evaporator core depending on the temp setting on the dash.

The blend-air door actuator on a 2008 Merury Grand Marquis is located on the top forward area of the HVAC housing under the instrument panel. Complete instrument panel removal is required to access it.

control head is probly bad

A blend door is located within the air distribution housing, under the dash. This area is very delicate to work on and it is easy to destroy non replaceable parts. I suggest that a qualified shop do this job for you...

Look for worn, damaged, or loose vacume hoses..

blend door

This sounds most like a worn lock actuator which wouldn't be uncommon. If you need a diagram on how to replace, let me know.