Hey gang,

When I have the vent on in my 04 QC (AC is off), it seems like the air coming from the vents is noticably warmer than the air temperature outside. I have noticed this ever since the truck was new and thought it might be normal. However, I find it odd that I have to run the AC when it's 65 degrees outside here in Atlanta. I've not had this problem in other vehicles I've owned (too many to list).

Has anyone else noticed this as well?

Mike

 

Mine does the same thing when sitting out in the sun. Doesn't matter what the outside temp is. I think the sun warms up the ventilation in some way. I just turn on the air for a short time and then turn it off.

2002 QC 4.7 3.92LSD

 

I noticed the same thing the other day when it was finally 65 in south Florida. I ended up just rolling the windows down.

 

This happens on my 04 1500 QC. I have noticed that HVAC blower housing is warm to the touch when the problem occurs. Mine happens at night, so it's not an issue of the sun heating up the interior. I have noticed that my problem tends to show up more when I have driven the truck for a while, stopped, and then resumed driving. One time, I opened the rear window on the passenger side and heard a sound from the blower unit that sounded like a flap closing. The warm air stopped. I've gone to the dealer and all they say is that there are no Diagnostic Test Codes (DTC)s. My son who worked as a mechanics helper at a Dodge dealership, said they had a lot of complaints caused by malfunctions of the bi-level door mechanism failing. Looks like the only way to verify the door are working properly is to disassemble the blower unit--a lot of work.

Roger...

 

prolly the heater core heating up as you drive the truck, coolant is going to run through it and it is going to get warm regardless of whether it is on or not.

"I noticed the same thing the other day when it was finally 65 in south Florida. I ended up just rolling the windows down."

it is just now getting to 65 in south florida? I have been enjoying 80 here in nw florida

 

Finally traced down the source of my problem. After driving the truck for 30 minutes+ in warm weather, the firewall and floor underneath the dash and the HVAC gets noticeably warm. This heats up the HVAC box that, in turn, heats up the air pushed through the vents. In my case, the vent air temperature averages 10 degrees "warmer" then the air outside the truck--as measured with a refridgeration thermometer. If the outside air termperature is cold enough, <60F, then the firewall heat and outside air temp is tolerable. >70F and the vent air temp is 80--not good. I guess I'll explore heat shielding on the engine-side of the firewall to see if that makes difference. Might try better insulation under the carpet, but that's a lot of work and does nothing about the heating of the outside air intake due to a hot firewall. I'll let you know the results in a few weeks. I'm planning a summer trip on Route 66 and won't be able to survive the warm air when its 112F outside and the A/C won't blow under 80F.

Roger...

 

While surveying the cabin and underside of the truck trying to figure out where/how to install additional heat shielding to reduce the heat gain in the HVAC box, I discovered that the A/C drain is a 5/8 inch pipe that extends straight into the engine compartment. I occurred to me that under certain conditions, heat from the engine compartment could backup into the HVAC box and cause the warm air heating.

This occurs most frequently when I've stopped the engine for 5-15 minutes and resume driving. In this situation a huge amount of heat--and pressure--buildup in the engine compartment. I believe the heat and pressure backup into the HVAC box and result in the warm air experience. This is consistent with the warming I could feel on the bottom of the HVAC box.

So I bought a 5/8 heater hose with a 90 degree bend from Napa for $17. Cut it to fit the A/C drain and hang down to the frame rails. Low and behold, the average termperature difference between the vent and the outside air dropped from 10F to 5F without the hot humid air that had plagued me in the past.

Might be worth a try. At $17 and 15 minutes, the cure is a lot easier and cheaper than heat shielding.

Roger...

 

You guys should be on Jeaprody...

 

More surprises. After fixing the A/C drain problem, I was still encountering warm air from the vents sometimes 8-10 degrees warmer than the outside air. Feeling around the HVAC box, I could tell that the firewall wasn't warm enough to cause that level of heating.

I then noticed the area around the blower motor resistor was "hot." I removed the resistor and the darn thing burned me. Turns out the resister is really nothing more than a little electrical heater encased in ceramic. The darn thing puts out tremendous heat when running the blower motor on low. That's why Dodge locates in the HVAC box right next to the fan. The fan keeps the resistor cool enough not to set the plastic aflame.

So it looks like the majority of the heat is coming from the blower motor resistor in the HVAC. Apparently, there is nothing that can be done short of installing some kind of alternative. It appears that these resistors are a common design solution to inexpensive variable speed DC motor operation. In other vehicles, these resistors are often located outside the passenger compartment and are often subject to premature failure due to corrosion.

So, bottom line, it appears the primary source of heating is caused by the blower motor resistor and there's nothing we can do about it but crank up the A/C when its only in the 70s.

Roger...

 

Not only does my 04 Hemi do it but both of my PT's do it too. I think it a Chrysler thing. Every one in the PT world has the same problem.