Blower motor runs backwards

[zachmac]

So , I am working on the Fiat and among other items pulled the heater box to change out the heater control valve and check everything out. I wanted to test the motor and as I have the battery sitting in the trunk I opened it to hold the wires from the motor to the battery and test both speeds. The good news is it runs fine, two speeds. But, unless I am missing something it seems to be pushing air UP toward the heater core. Shouldn't it be pulling it down and out toward the floor exit and defroster plenum? I had the black wire to negative and the switch lewds alternately to + so it should have been running as normal?

BTW, this was right before I closed the trunk locking my only keys inside!!!! See next post.

[majicwrench]

On most vehicles, the blower motor pushed air thru the heater core, then out the vents.
Keith

[zachmac]

On most vehicles, the blower motor pushed air thru the heater core, then out the vents.
Keith

On MOST vehicles, BUT but on our cars that would mean the air was getting pushed out of the car through the "fresh air" inlet.

If you've never had one of our heater boxes apart then you may not realize how simple and crude it is. The air comes in ONLY via the flap to the outside world under the wiper blade cowling. If that is closed you have basically NO air flow. There is no recirc path.

Once the air enters via that inlet it passes immediately over the heater core into an area below where the fan resides. The fan if on should pull air down and dependent on the "defrost" lever setting either send that air to the floor or back up a separate plenum on the front side of the box to the defrost vents. The "defrost lever" simply open or closes the big door at the bottom of the heater box to allow or block flow out the bottom. When blocked it forces the air back up to the defrost vents.

The third lever is connected to the temperature control valve. Ironically, when pulled all the way toward the back of the car (toward the RED arrow on the center console icons which you would think is HOT verus the blue which you would think is COLD) it shuts off the water flow to the heater core,

Again, the air flow is ALWAYS in from outside the car, across the heater core and out via the bottom or defrost vents. If the outside air inlet is closed you should have very little air flow regardless of fan speed. This is why a faulty heater valve gives you hot air, the heater core is ALWAYS in the flowpath.

All of which doesn't explain why my fan is running backwards?

[zachmac]

Never mind! Once you assembly the top have it blows air the way it is supposed to blow it (as described above). I think my problemwas that with just the motor in the lower half and none of the surrounding pieces the fan only "seemed" to be moving air the wrong direction.

BTW, a couple of quick bench tests confirms that air flow is VERY dependent on the position of the "fresh air" inlet flapper. Close it down and you don't move jack!