I recently had a shop replace a leaking heater core. While the dash was off, I had them fix several things, including a 2-year-old problem with the HVAC air directional controls. The air blows out of only two sets of vents (dash and defrost OR dash and floor). When it blows out of the dash and floor, the defrost blows to floor. When it comes out of the defrost and dash, the floor setting blows to defrost. It seems to change between the two "options" at random, so at any time, I'm either without heat or without defrost...great for winter driving!!!!

The shop replaced/repaired the blower door housing, the door inside the housing that directs the air, and the drive motor for the door. It worked for them and it worked for me during one run through...dash, heat, defrost. But, after 1 or 2 run-throughs on the dial, it would only blow in two directions like before. So, I left the truck another day.

The shop next re-oriented the drive motor gear on the diverter housing and put it back on the unit. Again, it worked for them and it worked for 1 or 2 run-throughs between dash, heat, and defrost. But then it started doign the same thing again. By that time, the shop was closed and I need my truck and time to think about next steps.

Any ideas what to look at? This wouldn't drive me so nutz, being a 2-year-old problem. But, since I've dropped $1000 bucks on these repairs, and the shop will make the repairs for only the cost of any additional parts (assuming we can figure out what's causing this) I'd kind of like to help these guys get to the bottom of the problem and get back all three HVAC options!

Please help...it's still cold in GA and I need my Dodge heat!!!

 

I had this problem in a vehicle a while back. Ended up being a vaccum leak in the lines to the controls. Not sure if yours is all electical but it might be a place to start. Hope it helps.

 

I originally assumed vacuum, too. BUT, the mechanic explained that floor/dash/defrost air diversion on this truck's HVAC is electrical. From what I can tell from the ONE picture of the heater/AC unit in my Hayne’s manual, there are 2 (and maybe a third) “air boxes” under the dash. Each has an internal diverter door that’s driven by an external electrical motor and gear assembly.

Might the 2003 Ram 1500 diverters be at least partially driven by vacuum (i.e., the motors allow the diverter to move to a particular orientation, but vacuum actually makes the door move)? If so, I do occasionally hear a slight sucking sound when I accelerate (possible vacuum leak) and perhaps week/surging/variable vacuum could be the cause of the intermittent nature of the problem?

Or, is the movement of the diverters exclusively electrical? If so, any idea which of the 2 or 3 “air box” motors is the most likely culprit of the alternating dash/floor or dash/defrost-only problem? Each air box/door/motor unit is sold as a complete assembly and 1 was on WAY-back-order via the dealer, so hit/miss replacement will be time consuming and expensive. Given that the problem is intermittent, I doubted this theory because I would think that an electrical component is either good or bad (so I’d assume I’d have either dash/floor only OR dash/defrost only ALL of the time...which is not the case).

My last thought - if all is electrical - is that perhaps the gears on the electronic diverter motor gears must be rotated and oriented in a specific way when the drive unit is installed to the air box. If they jump a worn gear or get re-installed out of orientation, then diversion is out of sequence with the switch. If that’s the case, perhaps the intermittent nature of the problem stems from the out-of-synch motor and/or worn gear trying to turn against a fully open/closed door and, under power, it finally “jumps” a possibly worn tooth on a sprocket?

Can anyone verify or debunk and of these theories to help me narrow down a likely solution(s)?

 

Since this problem is intermitten it will take some real knowledge of how everything works. I would go to the junk yard and see if there is a truck you can pull apart to gain some insight on how everything works. If it is all electric, there maybe some mechanical motor stops that require adjustment or a gear slipping on a shaft. Basically I am just thinking out loud.

 

After finding and reading some addional information and watching a 3-part diagnostics video from heatertreater.net, my issues sound like they may result from a faulty "mod-3" blend door/housing/motor assembly. I'll have to disassemble to validate that theory, but the way I understand this component, mod-3 diverts air 90/10% defrost/floor OR 10/90% defrost/floor to create a blend of heated air to the floor and defrost (as apposed to other blend door assemblies that force 100% to one or the other).

I'm thinking this component might be the culprit because today I'm noticing that when I'm able to get strong air at only the defrost or floor, I still get a trickle at the other oraface...even when I have the switch set to provide 100% from either. I assume that mod-3 door hinge or pin is either broken or cracked and when I set to only defrost or only floor, mod-3 (broken) is still trying to create a blend.

Unfortunately, the vid said that removing/replacing mod-3 requires a tear-down AND cutting out a section of a welded metal dash bracket....ugg, if that's the case! Anyone know of a way to validate if the mod-3 blend door is broken...without having to disassemble the entire dash...is it visible/reachable via the driver's-side heat outlet?