Forum Discussion

mustang071's avatar
mustang071
Explorer
Aug 28, 2019

What;s Wrong With My RAM Truck????

Our 2005 Ram 3500 Diesel (5.9) SRW has been a great tow vehicle for our 7-ton 5th wheel trailer. And after 150 thousand miles, three years ago we had to replace a couple of leaky hoses in our air conditioner. No surprise there. Since that repair, the AC blows cold and steady, towing or not. EXCEPT.

During this past year, on our last three return trips to Texas- one from the Great Lakes and two from Colorado- the blower quits working at about 350 miles from home. The AC is constantly cold, but without the fan blowing, we get very uncomfortable and downright HOT in the cab driving home in the Texas heat. In fact, on the last two trips, the blower quit in exactly the same place, a few miles south of Amarillo heading down 287 towards Dallas.

Each time, we’ve managed to get a little action out of the AC fan IF we can keep the RPM high as we travel. But if we stop at a red light and the engine is at idle, we get nothing. Cracking the window seems to help the blower also, but engine speed seems to be the key. Once on our last trip when climbing a hill, the tranny dropped to low and the fan started working perfectly as the RPM climbed to about 3000. But that lasted for about 3 minutes before dropping back into pathetic, weeny mode.

The Dodge House is clueless; they said the system only needed service which was performed prior to our most recent travel, but that had no positive effect on this fan problem. The AC works perfectly around town and all during the trip, except for the very last 350 miles.
Has anyone out there in RV land had this issue? If so, how did you fix it? Help!
  • It isn’t clear in the original post whether the blower motor actually quits running, or if it continues to run but the airflow diminishes. Determining this is a key part of diagnosing this.
  • I had a 2500HD that would stop blowing cold air at stop lights and at low speeds. The blower fan would still blow but the air was hot. It took me a few weeks of research but I found out the fan clutch had failed, causing the evaporator to freeze up.
  • Fans And blower resistors are common in those year trucks. I've also run across a few that had a burnt connector under the TIPM (underwood fuse box). Should be a simple problem to find.
  • What does it do if you pull over, turn off the truck for a few minutes, then start it up again? If it blows normal, then what ever electrically resets the blend door is your issue. I have had that now in 2 Rams and a 2 Fords
  • ScottG wrote:
    Sounds like low freon level is causing the evaporator coil to freeze up.
    It will be worse when humidity is high or eng speed is low.


    I don't know about freon level but I agree sounds like the evaporator is freezing up.

    I have seen this in a fleet I support, but they're F150s. AC works great for a bit and slowly fades to nothing.
  • ScottG wrote:
    Sounds like low freon level is causing the evaporator coil to freeze up.
    It will be worse when humidity is high or eng speed is low.


    Highly unlikely. Low freon level would result in poor performance. The system blows cold. Therefore, the freon level is perfect, or close to it.

    You may be on to something with the icing of the evaporator idea though. The system should have some sort of switch (probably a low pressure or temp) that cuts the compressor off to prevent this.
    In my mind this is the most likely cause. The OP can test his theory out without any tools or even lifting the hood. When it happens, simply turn the AC of for a few mimutes. If it is iceing, then it will melt, then work perfectly when it is turned back on, until it ices up again.

    I am not sure if this is a orfice tube or expansion valve system.

    If it is an expansion valve system, then that may be acting up.
    This is a more involved fix though.

    I would look for a compressor cutout switch. They are cheap at 15.00 or so, and easy (5 min) to install.

  • Sounds like low freon level is causing the evaporator coil to freeze up.
    It will be worse when humidity is high or eng speed is low.
  • I'd try a new blower fan/motor assembly. They aren't very expensive, and super easy to change out. A few screws under the dash and it's out. Could also be the resistor/fan speed control. That is also easily accessible right beside the blower. 1AAuto.com has a video on it if you're not handy.