Attention: TDR Forum Junkies 
Mike Wenrich
TDR MEMBER
So those following my blend door posts on my 2004.5 truck might be interested in the next job on my neighbors truck. It's a 2003 Laramie with the 5.7 Hemi. The heater/defroster and A/C has not worked for years and with experience under my belt I took hers on as I figured it was just another blend door issue. It turned out to be a different issue. The lack of air flow was suspected to be a broken door...like mine. But when I removed the dash and got into the plenum there were no broken doors. Also the doors were different than my originals and much more stout.
But the A/C evaporator was 80% clogged with a fine debris. Searching for the reason I noticed the filter screen on the firewall had some debris on the bottom, kinda like a clothes dryer lint screen. When I removed the screen to clean it I found a large amount of nest material made by a rodent. It had been there a long time and would have completed the air block problem to the heater core in the plenum. As you know the air goes thru the evaporator to the heater core and the interior after that.
So how did it get in there? After cleaning the air chamber I used a mirror and light to see across the bulkhead for more material. The area is curved so I could not see all the way across to the driver's side but no more material spotted. Taking off the wiper blades and air vent grills I would not be able to see much more than that anyway. On the inside vertical wall of that area, to the right of the screen, there is a open oval shaped opening going into the passenger side of the cowl and down "somewhere" between the firewall and inner fender area. Could not see anything from the engine side but there is obviously a space large enough for said ratta to get up and into the air box.
At first, I thought the hole might have been covered by a body plug but I saw no evidence of one unless it was missed at the factory. Then maybe blocking the 3x2 inch hole with tape. But what if it was supposed to be there? The only thing I can surmise is that in case the intake grill on the top is blocked by leaves, this would be secondary way for air to get into the plenum. So this entire issue was caused by a rodent. While in there I replaced the blend doors anyway as they were plastic plus the heater core (it's 20 years old) and the A/C evaporator because it was so blocked by debris and sticky possibly from urine, etc. I was not able to thoroughly clean it.
To conclude, things are not always what they seem to be. This post might help others if you encounter a problem with air flow. I can't say I would do anything different as you have to remove the dash anyway to clear the blockage but you might remember to look behind the screen while in there. The 2003 works great again as designed and the widow is happy she does not have to wear four layers of clothes to drive it in the winter. She would not have been able to afford this repair if taken to a mechanic.
But the A/C evaporator was 80% clogged with a fine debris. Searching for the reason I noticed the filter screen on the firewall had some debris on the bottom, kinda like a clothes dryer lint screen. When I removed the screen to clean it I found a large amount of nest material made by a rodent. It had been there a long time and would have completed the air block problem to the heater core in the plenum. As you know the air goes thru the evaporator to the heater core and the interior after that.
So how did it get in there? After cleaning the air chamber I used a mirror and light to see across the bulkhead for more material. The area is curved so I could not see all the way across to the driver's side but no more material spotted. Taking off the wiper blades and air vent grills I would not be able to see much more than that anyway. On the inside vertical wall of that area, to the right of the screen, there is a open oval shaped opening going into the passenger side of the cowl and down "somewhere" between the firewall and inner fender area. Could not see anything from the engine side but there is obviously a space large enough for said ratta to get up and into the air box.
At first, I thought the hole might have been covered by a body plug but I saw no evidence of one unless it was missed at the factory. Then maybe blocking the 3x2 inch hole with tape. But what if it was supposed to be there? The only thing I can surmise is that in case the intake grill on the top is blocked by leaves, this would be secondary way for air to get into the plenum. So this entire issue was caused by a rodent. While in there I replaced the blend doors anyway as they were plastic plus the heater core (it's 20 years old) and the A/C evaporator because it was so blocked by debris and sticky possibly from urine, etc. I was not able to thoroughly clean it.
To conclude, things are not always what they seem to be. This post might help others if you encounter a problem with air flow. I can't say I would do anything different as you have to remove the dash anyway to clear the blockage but you might remember to look behind the screen while in there. The 2003 works great again as designed and the widow is happy she does not have to wear four layers of clothes to drive it in the winter. She would not have been able to afford this repair if taken to a mechanic.
