Air/heat issue

[Whiskytango]

Hoping for guidance on heat/air issue. Here goes. 2001 ram3500, 5.9 cummins 6 speed. 280 kms. All the vents and settings work, all fan speeds work. After 20 minutes of driving, everything goes to barely working. Almost like a towel is covering the whole system.Fan on max sounds like its working, air is cold or hot just not coming out with anyforce. Stop to fuel up or after truck is turned off for a bit, everything works again for that 20 + minutes. Have checked air pump, air conditioner is fully charged, Vacuum checked lines under hood. Any ideas ?

 

[Slinge]

does your truck have a cabin air filter ?

 

[Whiskytango]

No cabin air filter.

 

[Rob2gen]

Don't know if you have figured out your issue but I have a similar issue with my 01. I keep a rubber mallet handy and when my fan stops blowing, I tap the blower (underneath the glove box) and then it starts blowing again. I replaced a part about 5 years ago that was supposed to fix the problem (some ceramic capacitor thingee that wired into that area of the heater) but still have the problem. I also have replaced the fan. So I just give it a whack once in awhile and it takes care of the problem until I can actually figure out the real fix.

Good luck!

 

[Whiskytango]

Thanks Rob gen for answer. Like I said everything works as it should. Air or heat comes out all openings as per knob setting. Fan blows as per speed control setting. Everything does what its suppose to , but only for about 20-25 minutes. After that you can feel cold or heat coming out the right vents, you can hear the fan switch speeds and working as per speed switch, just coming out vents at a trickle. I dont know lots about this system and would like to have something to look for before tearing into it.