I am having the same problem with my 99.5 F-250 7.3L ---- the blower motor is simply weak. Blower runs on all settings and changes speed just fine. But the HIGH setting is just pathetic, even only on vents with Max A/C, and with one vent manually closed (either driver or passenger side). It just doesn't cut it in the Georgia summer heat!
Over the past 2 days, I've done the following:
- removed the glovebox and verified proper movement in both the blend door actuator, and the re-circ actuator
- removed the cover from the heater core and checked for debris (found little to none)
- removed the blower motor, checked for debris in the re-circ box plus on the evaporator core (found little to none)
- vac'd, sprayed compressed air, then a tiny bit of WD and then more vac, then a tiny bit of silicone spray into the blower motor windings themselves
- the blower motor turns just fine and doesn't seem to have a lot of resistance to it, although the plastic fan portion itself is still labeled 2/99 so it is original. I'm not sure if the motor itself is original.
- removed the blower motor resistor, looks normal, also can see more of the evap core in there too, looks a little dirty but not caked on
- vacuumed out all debris I could get to, along with the drain on the evap box. Is the evap box drain supposed to have a hose coming from it? Mine is just like a grommet and it empties out behind the fender wheel well. And it still doesn't seem to drip a whole lot, like some of my other vehicles do.
- found a small leak of R134 from the backside of the compressor, where the 2 lines mount in , there is a small bolt on the bottom of the block that mounts both the hi and lo pressure lines, that was a tad loose so I tightened that
- removed the cowl cover to check the drains and removed gunk in there, this truck lives outside underneath some big trees which dump stuff all over it all year
Ended up putting one can of R134a in there since it was on the low side, especially since the ghetto refridge hose you get from the local auto parts store sprayed out some 'fridge when hooking it up. Receiver/dryer lines are ice cold and they sweat plenty good, which is as they were a little while ago until I guess the small leak opened up.
The other mystery is that the re-circ box seems to collect water. It did drizzle a little last night and the hood was only latched shut (i.e. just like if you would pop the hood open), but it seemed to catch water in there easily. It was parked on a very slight uphill too. and there has nearly always been a musty/watery smell in the cab after the truck has sat for a while. I guess I need to try to seal up all the cowl area better to keep water out of it.
I'm perplexed as to why Ford decided to mount the evaporator in the engine compartment, but the heater core in the cabin side?????? This engine gets so warm naturally because its HUGE and its HOT, and the bellhousing projects in towards the cabin so far. The truck gets warm pretty easily just by the engine itself, I barely have to run the heat on any setting other than low fan speed. Why have the cold part (evap core) right next to a cylinder head, in a poorly insulated plastic box?????? It should be reversed, but I'm just a lowly aerospace engineer so what do I know.
I have also verified that the blower motor is getting 14.27 volts at the blower motor plug. So it does not appear to be a juice thing, considering the googling I did turned up a lot of websites for the 80's Ford trucks and having weak voltage being supplied to the blower (everyone seemed like doing a relay mod to feed straight 14.2 volts to the blower would "supercharge" the blower).
Another interesting thing I found while googling is that some folks put manual valves on the heater hoses, which run to the heater core. That is, close off the hot coolant flow completely to the heater core during the summer. Sounds like a novel idea to me, and not expensive or that difficult. Thoughts?
Anyways, I guess for now it's as good as it's gonna get, I finished all that up and changed the oil and proceeded to spill it everywhere in the driveway, so tomorrow I will have to pressure wash and just go out an dial up some boost to bring a smile on my face to oppress my worn hands and dirty nails.
Any suggestions to try and up the CFM capacity in the cab?????? It looks like a blower motor is about $35 from the local parts place, but you have to swap the plastic fan which is probably easier said than done (I picture myself prying on it and destroying it).
For all of the above, I spent nearly as much time doing all that as I did trying to get the STUPID 3 little rubber stand-off mounts back on that fuel soleniod thing which is right in front of the blower motor. That thing frustrated me so much, that I gave up and zip-tied it.