poor flow through HVAC vents

[rocklobster87]

2008 F-250 XL/5.4

Truck has consistently weak air flow out of all interior vents. Mode and blend doors appear to be functioning properly. Defrost vents seem to be more restricted than others flowing almost no air at all. Recirculating improves air flow some but not much. I used a long blow gun and a vacuum attachment to clean out the HVAC inlet in the cowl (which did have some pine needles and such built up on it) and found no noticeable difference in flow. I am assuming the inlet and possibly the heater core and evap. core are simply plugged up with dirt and that I will be removing the dash to deal with this. Just want to make sure I'm not overlooking something before I do.

This vehicle is used for Wildland Firefighting and sees a lot of dust/dirt and a lot of A/C use.

No noticeable difference in flow whether at max heat or max a/c.

Truck has been acting this way since around the 25,000 mile mark.


Thanks in advance.

 

[m78]

Any chance of mice building nests in the ducts ? Where is it parked at night ?

 

[blacksnapon]

You may be right about dash removal. What you might try first though, is remove the blower motor, then reach as far as possible to clear the ductwork. We've also seen some breakage of the mode doors where the actuators engage the doors. Actuators still work, but nothing changes.

 

[Austin]

I had an issue like this in my Lincoln; I replaced the harness to the blower motor and everything was like new.

 

[DNFXDLI]

The blower wheel isn't spinning on the motor shaft is it?. I had this happen on my 05.

 

[rocklobster87]

thank you for the replies.

The truck parks outside in a gravel lot and sits for as long as weeks as a time. I have removed the blower motor and observed it operation. No signs of blockage visible from the port for the motor. No material in the hamster wheel whatsoever. Swapped in a motor from another rig and no change. Motor makes 4 distinct speeds. Mode switch directs air to selected vents and selected vents only. Just no damn flow. We also have another which does this with A/C running. Might be looking into custom cabin filter setups somehow. . .

 

[blacksnapon]

thank you for the replies.

The truck parks outside in a gravel lot and sits for as long as weeks as a time. I have removed the blower motor and observed it operation. No signs of blockage visible from the port for the motor. No material in the hamster wheel whatsoever. Swapped in a motor from another rig and no change. Motor makes 4 distinct speeds. Mode switch directs air to selected vents and selected vents only. Just no damn flow. We also have another which does this with A/C running. Might be looking into custom cabin filter setups somehow. . .

Yeah, you've got a broken door.

 

[rocklobster87]

Yeah, you've got a broken door.

can you explain? The blend door works fine and the mode door directs air to the selected vents and the selected vents only. Recirc door appears to be working as well. Is there another door I'm not aware of? Either way it sounds like i'll be pulling the HVAC box so i guess it doesn't much matter. .