My A/C fan has begun to run at speeds that fluctuate, including ceasing operation altogether – which is a pain in the heat this summer. These trucks are noisy so it is hard to determine the fan speed (although it's easy to determine when it quits completely). But when I turn on the switch key (without actually starting the truck) the fan starts sometime and other times is dead as a doornail. When it is running, the speed seems to fluctuate from high to low.

What is the most likely malfunction?

TIA

 

Replace your blower motor,

When the blower motor gets intermittent it is usually the brushes have worn down to they only hit the commutator at times or when you hit a bump.

As long as you know you are getting power to the motor you just need to replace the motor, I got a lifetime one from Auto Zone.

Jim

 

James:

Thanks much.

Briefly, what is involved in the replacement? Can it all be done from under the hood or do I need to tear into the HVAC unit inside the cab?

Thanks again,

 

All under the hood.

It may be underneath an insulating blanket but it is a straight forward R&R.

 

I think all you need to do is to remove the insulating cover from the motor, remove the vent tube from the back of the motor housing and after you remove about 6 screws the entire motor and wheel assembly will drop out.

The replacement motor will have only pigtails to connect back up to your harness, you will have to match the rotation of the blower wheel, if you connect it backward it will run but you will not get very much airflow from it.

Jim

 

The last several weeks, the blower on one of our trucks has been not coming on when first turned ON, regardless of speed selected.


No amount of wiggling/fiddling with the A/C or blower controls will make it work.

To get it to work, run a power-window up/down ONCE; the blower will then kick in and work flawlessly the rest of the trip.

This might have made more sense a few months ago; but, the power-windows are wired completely independent of any of the factory system; no fuse-block connection and no key-switch connection.


UNLESS, both the power-windows and the blower are connected to the same GROUND point.


It has been hatch-an-egg HOT, so I haven't been real industrious about investigating the situation, so long as it works as well as it is.


Anyone else ever had the same issue ??

 

Mine would cut out every once in while. In the past I've popped the hood and smacked the motor with whatever solid object I could find and it comes to life. It hasn't cut out in a while though but I'm sure it's in need of replacement. If it does anytime soon, I'll try the window trick.

 

Bear, you sound like a 3rd gen with the power switched at the key, and that can be a problem.

there is a thread on changing, if it's a 3rd Gen.

https://www.dieseltruckresource.com/...light=hvac+fan

if not, see where the window & AC cross paths, ??

 

No, not a 3rd Generation.

Nothing in my fleet that is not fully mechanical.

 

Someone will no doubt be reading this thread in the distant future. So, for posterity:

I replaced the fan motor and that cured my problem. (Thank you, James Lane.) I bit the bullet and ordered a Mopar fan from my local Dodge dealer. The OEM fan was Denso, the Mopar replacement unit was Siemens. The orange wire on the new motor connected to the green wire on the old pigtail and the fan spins correctly. (Black wire on new motor goes to black wire on pigtail.)

Removal of the insulating heater cover is a bear. It is made in two pieces held together by one screw and a Velcro tab; there is no reason to remove the piece closest to the passenger fender -- just leave it in place. The other half is attached to the firewall with three sheet metal screws having 5/16" (or 8mm) hex heads. One of the screws is directly behind the little cylindrical transmission cooler (under the turbo) and the spacing is so tight a ratchet or nutdriver won't work -- an 8mm box end wrench did the trick. Once the insulating cover is out of the way, there are only three screws securing the motor and squirrel cage fan to the heater unit. Replacement of both the motor and the insulating cover was no more difficult than removal.

My new fan motor seems to blow about the double the volume of air when compared to the old one. Thanks again to all.

 

With similar symptoms as those you were having, THIS is what our problem turned out to be :

https://www.dieseltruckresource.com/...o-t275664.html


The key-switch apparently was our culprit.