94 Ram air only at floor?? update 6/20

[old head]

This is an issue that has been betting worse over the last year, not a sudden event.  It seemed like the velocity and volume of air coming out of the vent and defroster was minimal to the point we had to use the highest fan speed all the time.
About 3 months ago, it got the point where the defroster wasn't clearing the windshield especially when it rains, which is often in south Louisiana.  Got to the point that the wife won't drive the truck.
So I pulled the dash, and the heater box and replaced the evaporator and heater core.  I also replaced all the doors in the heater box along with new foam.  I did find a broke door, but no change in volume or velocity after reinstalling dash.
All the doors moved with ease after putting the box back together, but since everything is vacuum, I had no way to check the volume until I could put it back in the truck.

With the motor off, diesel, I can hear the fan running and I do get air out the bottom, but really not much air unless on highest setting.  with the engine running, I can see the actuators moving, and can visibly see the doors moving, well except the one that directs to vent or defrost, the actuator arm is moving, so I assume the door is moving as I can't physically see it the door like the other doors.
there is a fresh air door above the glove box, I can see that moving, a door that controls the heat to a/c ratio, door that directs to floor, and a door that directs to vent or defrost.

I am really stumped.  The fan blows on all 5 speeds albeit low volume out the floor, even less when defrost or vent selected.  I can feel some air on high, but very light.  Virtually, nothing with the lower speeds.
Is it possible that the blower motor is worn to the point where it just can't spin fast enough or could it be the blower resister is weak across all circuits such that it is slowing down the motor?  I am not confident when dealing with electricity so, thoughts?  Could it be both?  I have never had to change a blower resistor in any of my cars, have changed the blower in this truck once, its a 94 with about 350k.  Seems it was about 10 years ago when I changed out the blower, but not certain.

Its about a 6 hour job to pull the dash and heater box and replace it, so....

Old Head

[Tom]

Hope you can pull the fan out again.  Seems from what you said the fan isn't spinning fast enough.  The internals could be corroded.  Check to see how freely the fan blades move.  They should be pretty loose.  Your high humidity could have corroded the stator & rotor.  Take apart and clean off the corrosion.

[Muzz]

Is there a filter in the system?

If there is, it may be blocked.

[Tom]

I don't think his truck has a cabin air filter.  Correct me if I'm wrong.

[old head]

no cabin filter.

[Tom]

Your fan blades in the motor should spin easily.  Hope that's readily accessible.

[rschrum]

Put 12v directly to the fan motor. If it blows harder, its the resister pack, if not its the fan.

[GeorgiaGuzzi]

I have a 97 Cummins. If I remember correctly it’s the vacuum lines that attach to the firewall. They get old and crack and little to me vacuum. I found some good videos on YouTube that explain much better than I can. Google “Cummins 12v mixer vacuum lines”. I think that’s what I searched. 556k on mine, so there’s a bunch of aged and non-oem fixes by now! Lol

[old head]

I have a 97 Cummins. If I remember correctly it’s the vacuum lines that attach to the firewall. They get old and crack and little to me vacuum. I found some good videos on YouTube that explain much better than I can. Google “Cummins 12v mixer vacuum lines”. I think that’s what I searched. 556k on mine, so there’s a bunch of aged and non-oem fixes by now! Lol

It appears to me that all the doors are working.  All the doors moved easily before I put the box back in.  removing the glove box, drivers side lower valance, and lower air ducts gives visual access to those doors and they all move.  Just the one I can't see, but the actuator arm is moving so it don't think its a door issue.

Tomorrow I plan to remove the blower  and compare the speed through the resister vs direct connection to power and see what happens.  I will probably pull the resister out and check it for cracks or corrosion.  If I don't find something obvious, I will just order a new blower and resistor and change them both.

I love the Cummings motor and manual tranny.   The rest of the truck well not so much.  Never buy another new Dodge, really cheap plastics and weak ball joints.  I know everyone does it, but putting the  heater and evaporator behind the dash is very poor engineering for ease of repair.  I miss the days when the evaporator was under the hood on the firewall.  easily accessible.

Old Head

[Two Checks]

You say the doors move but do they move with engine running and you move the controls?
If you have a vacuum leak when the vacuum drops, as when going uphill the doors will default to the floor position and when vacuum comes back they will go to where they should.

[Muzz]

Are the fan blades cupped.

As a former cleaner of heat pumps, if the unit was run on the aircon cycle a lot the fan blades ran damp, and any fine dust that got through the filters would stick at the start to the leading edge of the fan and then would slowly fill up the cup.  I have seen them where the fan has been completely filled and absolutely no air is shifted at all.

[old head]

Are the fan blades cupped.

As a former cleaner of heat pumps, if the unit was run on the aircon cycle a lot the fan blades ran damp, and any fine dust that got through the filters would stick at the start to the leading edge of the fan and then would slowly fill up the cup.  I have seen them where the fan has been completely filled and absolutely no air is shifted at all.

yeah, I had the motor running and tried each setting on the controls, each of the doors moved when appropriate selection was made.

[Muzz]

yeah, I had the motor running and tried each setting on the controls, each of the doors moved when appropriate selection was made.

Not actually referring to the doors, but the actual fan blades on the motor.

[Two Checks]

At idle the doors will work properly due to adequate engine vacuum.
But with a vacuum leak under throttle as in going up a hill the vacuum drops and the doors will default to the floor outlet.

[GeorgiaGuzzi]

Yeah, I love my powertrain. The rest of the truck not so much. It’s a million mile engine in a 100k truck! My dash looks like it was a victim of Thanos’s snap! And don’t even ask me about the door hinges!!!

[nc43bsa]

At idle the doors will work properly due to adequate engine vacuum.
But with a vacuum leak under throttle as in going up a hill the vacuum drops and the doors will default to the floor outlet.

Isn't the truck in question a diesel?

[Two Checks]

Oh...that's right.
So it should have a vacuum pump.

[RinkRat II]

     Yes, mechanical pump and the controls need at least 8 to 9" of vac. to stay in their position selected.

        Paul B 

[old head]

Update
Been really busy at work, just haven't had to get back at it with work and rain.
took some time today, I am only getting 10.5 volts at the fan connection with the fan set on high, truck running.  I get less voltage at each speed, which is what i would think.
wired the fan direct to the battery but not much change in speed, and certainly not any increase in velocity at the vents or defrost.
My meter shows 11.9 volts when hooked directly to battery.

Have a call to my brother who is an electrician and maintenance supervisor at a plant.  I am thinking its is a little bit of both.  Weak fan motor,  my thinking it should have really increased with direct connect to battery, but it didn't.
I think the voltage is too low coming from resistor when on high speed, I would think it should be 12 volts, right?
The fan doesn't squeal or make an abnormal sounds, just seems to be too slow to my ear.

Old Head

[nc43bsa]

With the switch on high, the motor should get battery voltage.

With the engine running your battery should be ~13.3V.

[Ryan]

If you switch from fresh to recirculated air, does the volume increase? Even without a cabin air filter, crap can get into the intake and cut your flow. If there is no difference, I second checking/cleaning the fan. Most bathroom air vents slow with age, and it is the moisture mixing with the lint from the TP and paper towels that over time clogs the fan.

[Tom]

 

[old head]

If you switch from fresh to recirculated air, does the volume increase? Even without a cabin air filter, crap can get into the intake and cut your flow. If there is no difference, I second checking/cleaning the fan. Most bathroom air vents slow with age, and it is the moisture mixing with the lint from the TP and paper towels that over time clogs the fan.

Ryan,
fresh air or recirculate, makes no change in air velocity.  I think if it was blocked that affect one or the other, but not both, right?  At any rate, I did pull the dash and heater box out and replaced all doors and foam 5/6 months ago, there really wasn't much of anything in the box to speak of and there isn't any  leaves or debris on the outside screen on the cowl that I can see.

My other brother has a 96 ram and I think I will see if we can swap fans to test to see if it is the fan, which I believe it is at this point, along with the resistor.

Old Head

[Two Checks]

This still doesn't explain why the air comes out only at the floor.

[Tom]

You heard of "heavy water"....then it's heavy air.    Sorry couldn't resist. 

[old head]

 I replaced the blower and the resistor, no improvment.

I guess I have to pull the dash and see if one of the doors have come loose.  Can't think of anything else that would keep the air from coming out the vent and defroster.
that is the only door I can't see moving, the arm is moving but I can't see the door.

Old Head

[old head]

The pivot pin fell out, the door fell out of position and blocked air flow.
there is no provision to secure the pivot arm to the door, so it appears the actuator arm pulled the pin out.
so I am using some Red loctite to hold the pin to the door, hoping that will hold it in place, its a male female connect, they just slide together.
hopefully later today it will be back together.

Old Head

[Tom]

Mystery solved.   

[GeorgiaGuzzi]

 

[nc43bsa]

Ain't dashboard work fun??