HVAC Blower Problem

[AFurrh]

I have gone through a lot of posts, haven't come up with a problem like mine (but it may be there!).



The vent blower on my sig truck varies speeds without a "command. " Sometimes it completely stops. Bumping the fan with the palm of my hand will change the speed; I only bump it when the switch is on high, and the blower has either stopped or is turning very slow. A bump or two will bring it back to high speed. It doesn't seem to have infinitely variable speeds, but seems to conform to the four switch speeds. I have gone through the service manual and haven't found anything that seems to help with diagnosing the problem, although I believe it has to be either the blower moter or the blower speed resistor. I get no codes. Any idea as to how to determine where the problem is?

 

[BGlidewell]

There is a post on here that addresses your problem. IIRC it involves a resistor type component. I've heard this happen in my truck as well but it is so infrequent that I have not looked into it yet. I know in my case it happens in hot or cold weather, heater or MAX AC. the fan slows down ~50% for a few seconds then speeds back up not to repeat again for months. I try to remember to look at the amp gauge while this is going on but some how keep forgetting... usually happens within 5 minutes of an engine start.

 

[jhenderson]

Generally speaking, a bad resistor will give you missing speeds( low or medium) not an intermittent problem. I would look for loose or corroded connections at the resistor and or the blower motor.

 

[B.G. Smith]

Since you live in Texas, your fan probably gets lots of use. My guess would be the brushes in the fan motor. Not serviceable, have to replace motor if that is it. The resistor is down there near the motor on the bottom of the AC houusing , next time it slows down try just tapping on the resistor and see if that does anything. bg

 

[AFurrh]

Thanks for all the replies.

Yes, the blower runs anytime the truck runs, so that is about 3,350 hours so far.

It occurs when either heat, cool, or simply ventilation is in use.

I have "jiggled" wires, but that has no effect. Pulled the connectors from the blower motor as well as the resistor mounted next to it; they looked clean and straight, so I cleaned them with contact cleaner anyway and reassembled them. No change.

The blower may slow down OR speed up as often as every few minutes, or may do fine for up to half an hour. On a rough road it happens very rapidly.

The resistor is so close to the blower motor that I think if I tap either one, the other gets the vibration also.

Would tapping momentarily re-seat the brushes?

Still scratching my head. Guess I will probably buy one part (either blower motor or resistor) and hope that takes care of it. I will be really confused if I end up buying both and still have the problem!

 

[rscurtis]

The motor is easy to remove. Run it on the bench with a battery and see what it does.

 

[B.G. Smith]

I agree with rscurtis, I would maybe run it direcrtly from a cigarett lighter hookup or on the bench. It will run high only of course but if it is the motor you should be able to isolate it. The resistor costs almost as much as the motor so you don' want to do that. Some vehicles have infinite speed control and the resistor is actually a solid state module and the fan speed switch is a rheostat and they will do weird things when the module goes bad but I haven't seen that in the Dodge Ram but it may be available in some models. If you rfan speed switch is like a four position then you probably have the resistor setup. bg

 

[AFurrh]

Thanks to all, but especially B. G. Smith and rscurtis. Pulled the blower and connected it directly to the battery. It didn't run at all until I gave it a little bump, then it ran VERY slow. With each bump, the speed would either go up or down! Had to be the brushes, but I had never seen a D. C. motor act the way this one did.

I replaced it with one from Pep Boys. Wish I had been able to afford one from Dodge or maybe Napa; the replacement runs smooth, moves plenty of air, but the motor is really noisy. Sounds like the brushes aren't seated, maybe it will quieten down after it gets a few hours on it. And no, it isn't rubbing on anything. I thought it might be, so pulled it back out and ran it in the open to make sure; same noise. Love this site!

 

[BGlidewell]

Thanks for the update. Maybe you can rebuild the old motor. I've replaced the recirculation door with the updated oem and am really looking forward to the blend doors when they go.

 

[AFurrh]

I will try opening up the motor this weekend. All indicators are that it can't be serviced/rebuilt, but I will give it a try anyway. Will let you know next week.

 

[B.G. Smith]

It's always good to have a good ending to a story. Glad you got it worked out. bg

 

[BGlidewell]

dealer wants $150 for the motor and $77 for the resistor pack. My truck has always had a very infrequent fan stop-wait 2 seconds-start, that occurred every 6 months or so but now it is slowing down every time the truck is driven more than 30 miles and if you turn off the fan, it wont turn back on. Next morning or drive home, repeats. My truck lives on hi-max-ac here from June-September.

 

[BGlidewell]

I slapped the fan motor when it stopped and it immediately came back on. I bought the replacement motor from the dealer but now the fan wont fail again.