My truck has done the same noise, for years. Only on one grade from Seattle to Utah, and one from Flagstaff to Phoenix. Any other hills, no noise. I still haven't figured it out yet.

 

I’m betting on it being the fan hub bearing. Never did it when the fan clutch was dead. Does it with two different FC and only does it when pulling a grade right when the fan kicks in. Hope I’m right!

Changing it right now and hope to test it this weekend.

 

Some thoughts about both your HVAC airflow, and your fan clutch

Your HVAC airflow problem is likely from inaccessible and broken 50 cent plastic Blend Door actuators at the heater box. After my wife said she would never ride in the truck in the winter if I didn't get heat back to the floor, I chose to remove the dash and partially disassemble the heater box. It wasn't that hard, but it helps to have a friend assist you getting the unbolted dash out of the truck. I pulled the dash because I wanted to preserve the dual temperature controls and didn't want to cut into the metal dash supports and into the heater box. I also figured I should replace the heater core while I was at it. I replaced it, but it looked fine at 225K miles.

IDK, but it may not even be faster to do the work in place with all the cutting and fumbling and swearing under the dash. Dorman reportedly has the plastic blend door actuator parts that break, or there are blend door kits you can find referenced on this forum.

If you do choose to pull the dash, take the truck to a radiator shop and have them discharge the AC FIRST. I didn't and it cost $240 to recharge it. They will charge you a lot less to put refrigerant in when they've taken it out and effectively held it for you. Put tapered rubber plugs in the AC dryer after removing the AC lines and it will be fine. Also, consider replacing the evaporator in front of the radiator. We noticed too late after recharging how bent a bunch of the fins were. Also, I hear that there are ways to add a cabin filter if you have the dash out. I heard that after I got it put back together.

Then, when the tech recharged the AC after I fixed the blend doors he noticed very high pressures in the AC system. My fan clutch was bad. I'd gotten an infrequent code about fan speed not being correct, but it went away each time. Dodge measures radiator fan speed, apparently.

The shop implored me to go with the $600+ OEM fan clutch saying they've had nothing but problems with aftermarket. They didn't mark the parts up so didn't really care from that perspective. I went OEM and all is well 65K miles later.

 

All great info, thank you. I have no issues with air flow though, the AC was reaching high pressure limit due to no cooling from the fan. It worked flawlessly at highway speeds.

Here are some things I have learned along the way that may help someone else:

A) The wiring harness where the wires go into the fan clutch itself are easily broken or disconnected when replacing the fan shroud. I place a piece of cardboard between them to prevent that now....
B) The 5v reading I got at the harness to the FC was actually correct. The ECM sends a pulse modulated (5v-12v) signal to the FC when it needs it, not a constant 12v like I thought.
C) Napa auto will "rent" a nice set of wrenches to make the job of replacing the FC painless. I have bought my own from Geno's garage now that are very handy.


I replaced my fan hub bearing and tensioner pulley this weekend and so far everything has been silent. Not a good test though, I need to hook up a trailer and pull some hills to be sure it is fixed.

 

I’m going to call it fixed. Had to take my side by side into the shop and trailered it an hour through a few decent passes here in Montana. Heard the fan cycling and ramping up and down as it should. The noise never returned in situations it did before.

Cannot be 100% certain due to replacing two bearings at once, but I’m betting it was the fan hub.

Thanks for all the tips and advice, much appreciated!