Hey everyone! Brand to this site. Hoping to get some answers. So my cab heater is acting up, it will blow warm to hot air through the defrost and face vents but will blow cooler air through the floor or any mix setting. Sometimes I will hear a thud or something dropping on the passenger side dash. I have a new radiator, thermostat, water pump, blend door actuator coupler (heater treater). I'm wondering if this is a vacuum or door problem, maybe even a heater core problem. Also on defrost from the driver vent to the passenger its got great air flow to almost none, so thats also a concern. Thanks! 

Edited December 28, 20177 yr by Beam52

Might have to pull the HVAC case and clean it out. I've seen some system where the foam peels off and binds up the doors and causes issues. Not to mention on my 1996 Dodge Ram had a BB in the vacuum motor and created a vaccum leak so the door randomly would flop open till the BB covered the hole again. PO spilled a box of BB across the dash and you guess it one found that vacuum motor. I've seen evaporators so packed with dirt and debris that the heat worked poorly. The only thing I can suggest is full removal of the HVAC box and split it open and clean and lube everything.

Hopefully I won't have to, tonight I didn't turn it to off most of the night shutting the truck off and on numerous occasions. The heat to the floor worked great. So I an thinking one of those vacuum pods, check valve or the control panel. 

There are no check valves in the system. There are only 3 vacuum motors which you will most likely end up pulling the entire HVAC case to even service them. Control panel typically never fails. Vacuum line issues under the hood are common though. 

Is this not a check valve that's in line?

https://www.google.com/search?q=2001+dodge+ram+vacuum+check+valve&client=ms-android-verizon&biw=360&bih=512&tbm=isch&prmd=sivn&source=lnms&sa=X&ved=0ahUKEwiBz9qcwa7YAhVNzmMKHTYFB7oQ_AUIvgIoAg#imgrc=tWyJ9oiy8SBECM:

Yes it is but this picture of a V8.   You find the vacuum check valve for the diesel module at the firewall top left of center, just to the right of the hydro boost.   It's at the end of the vacuum line from the vacuum pump.

That's what I thought. And this is for HVAC and cruise correct? 

 

Yes, just before the T fitting.

I'll have to look on my truck I don't think I've got the same set up being I'm fly by wire cruise control and the only thing vacuum runs is the HVAC. No vacuum cruise, No vacuum CAD unit (4WD). Might of changed up.

50 minutes ago, Mopar1973Man said:

I'll have to look on my truck I don't think I've got the same set up being I'm fly by wire cruise control and the only thing vacuum runs is the HVAC. No vacuum cruise, No vacuum CAD unit (4WD). Might of changed up.

Mine does have the CAD, early 02, and I think I have seen a check valve on mine but dont remember for sure where.