What happens on max a/c?
 

With the fan on high and normal a/c selected everything is fine. When I switch to max a/c the blower gets loud behind the dash but the volume of air out the vents is cut in half. The air does get colder, so I know it's doing the recirc thing, it just doesn't blow as hard as it's supposed to.

Haven't ripped the dash out yet....kinda hoping someone can give me clue what's happening in there before I do. I hate HVAC problems.

Sounds like a vacumn leak when the volume drops does air come out the defrost vents?

Check post 13
https://www.ford-trucks.com/forums/5...heel-well.html

I can shoot you a pdf with the diagrams if you need it cookie

Nope. Defrost, vent, heat.....every position works exactly as it's supposed to. The air that is not blowing out the vents is not blowing out anywhere...not the defroster, not the floor.....it sounds like the blower is ramping up up like crazy, it just doesn't make it out.

I appreciate the offer, but I've got the schematics already. I'm trying to figure out what the blend door is supposed to be doing and what the little actuator thingamabob under there is called.

Blend door should be closed (no vacumn) on Max AC. I cant find anything on the actuator.

Could the blower be clogged - blower spinning up but cant pull enuff air would make a heck of a racket

AC Max door positions

this sounds stupid, but reach up in the intake vent and make sure it's clear (blower off i imagine) i've done this several times to my Stang. wally world plastic bag from floor board gets sucked up (i live in my vehicles and they are quite cluttered), happened twice that I can think of. haven't taken a look at truck or schematics, but i would imagine recirc intake is in passenger floorboard. just a thought.

Cookie,

What you're describing is exactly what mine does. Max A/C reduces the airflow.

I thought it was "normal". We'll see, however.

Pop

On mine, if I switch from A/C to MAX A/C, without changing fan speed, the airflow increases... as well as gets colder. So, Max A/C blows harder than plain A/C, all else being equal, on my truck.

Every vehicle I have ever owned the vents have put out more air on Normal that on Max.

Mine's like Ryan's - on Max it feels as if it blows harder, and definately colder.

The colder I will buy for sure, but I think the harder is tricking you. It is nearly phsically impossible to blow harder because it is recirculating the cab air instead of sucking it in from the cowl area.

Just come in from checking mine. With fan on high, when I go from normal to max, the fan DOES blow quite a bit harder. Sounds like fan speed increases as well. It feels as if it is moving half again if not twice as much air.

I worked on a sport-trac one time that had dead squirrel in the duct.I took the blower motor out to discover this critter. Something you might want to check.

I've a better one than this. I have a T-Bird Super Coupe that sometimes sits for a year at a time without being driven. A family of mice moved into the housing, nest, pieces of paper towel, dog food for emergencies I guess. What a mess. I remember cutting the hell out of myself getting the damn thing apart and back together.

max should blow more than normal due to the fact that it's not trying to keep positive pressure on a cab that is more sealed than open. crack a window and normal ac might blow more since it is now free to blow air out the cab. definately sounds like an obstruction.