99 1500, 360 engine, a lot of miles (250K plus). We suddenly have very little heat in the cab of the truck. Temp. gauge shows normal operating temp. Both heater hoses hot to the touch - one more than the other. Have tested the check valves under the hood and both are good. Radiator is full of coolant.

Turning the temp **** in the cab from hot to cold makes the air slightly cooler and moving back to hot makes it just a little bit warmer. I can hear the blend door moving, but more air comes out the vents when the temp **** is set to cool than when set to hot.

My best guess is the blend door isn't fully functioning - clogged or something. Anyone have another theory?

Also, according to the manual I have for a 2001 model, getting to the blend door requires a major disassembly of the hvac system in the cab. Is that right?

Thanks guys.

 

Clogged heater core probably.

 

First try flushing the heater core.

Second, try this: http://www.heatertreater.net/magento...php/dodge.html

All 99 and up have this motor and problem but this guy made a solution. I dealt with it last year.

 

Hmm. With it happening suddenly and both hoses "hot". Engine still getting up to temp? Have your coolant dropped for some reason?(air pocket)

I would doubt its actually a plugged heater core..... Good luck

Jake

 

Well, as far as we know it was "sudden" in that the truck had heat last winter but not this winter. We have not added coolant in a while, so I doubt an air pocket is to blame. We just flushed the heater core and some brown gunk came out but not a lot before we got clear water flushing both ways. Kept hoses full of water while reattaching them so as to not create an air pocket, but problem still exists.

The blend door is still my primary suspect as Ramman suggested. From the shop manual, I was under the impression that the HVAC system had to be disassembled to get at it but from the video in the link it looks like it is accessable from the bottom passenger side of the plenum. Will look into that next.

Thanks.

 

Yep, little stepper motor right above the trans tunnel, just to the passenger side. If you twist yourself around into a pretzel, you can see it, and touch it. Getting the screw closest to the firewall out is the fun part. Cutting the carpet a bit to give you better site, and a tad more room, helps.

 

When I had no heat, it was the blend door being stuck... the foam seal had deteriorated and stuck it in the full A/C position.
Cycling the vent switch back and forth many times finally got it to break loose... lots of foam crumbs came out the vents.

 

That must've been what happened to mine (stuck) because after I removed the motor, the "interposer" was in good shape. When I reinstalled it, it broke. So then I had to order the heatertreater kit but I learned something new about these trucks and now it works near perfect. I didn't quite get the motor reset perfectly, but I have blend now. Yeah, the hard part is getting to the motor screw in the back. I bought some 90 deg screw drivers and only got a quarter turn each time. I think my back is still kinked from that one. . . .

 

Ok, this is really turning out to be a rabbit hunt. We pulled the blend door motor and inspected the black plastic interconnector and it looks like it may be cracked, but difficult to tell. So I drove the truck while my son held the connector on the bottom of the blend door and moved it back and forth. We get the same amount of heat as when the motor controls the blend door. Interesting to note that when the fan is up on high, it is nearly impossible to move the door by hand because of the volume of air coming past it. Regardless, the air is mildly warm at best.

With the engine off so it is quiet, moving the blend door back and forth with the connector, it sounds like the door is moving all the way in both directions and hits the appropriate stops. It moves very easily and smoothly.

Last thing I could think of was to push water through the heater core with a hose so I pulled the radiator cap and we ran a trickle of water into the heater core until it caused some air bubbles to discharge out the top of the radiator. Thought for sure that was going to fix it but it didn't. Hose going to the heater core gets so hot you can't hold onto it.

Is there any way to inspect the blend passages to see if the intake is leaking? Something has got to be allowing cold air to mix with what is passing over the heater core.

 

When you move the blend door, does the air temp change?

Disconnect the hoses from both sides of the heater core, inlet at the splice right above the passenger side valve cover, outlet side from the metal tube going into the water pump. (clamp off the hose closer to the water pump on the inlet side, and have something handy to stuff into the metal pipe, so you don't lose a bunch of coolant.)

Hold both hoses up above the level of the heat core, and THEN run water into it, from the outlet side. (the longer hose, or, drivers side.) Reconnect the hoses, keeping as much water as possible in there, and see how your heat feels.