1999 Dodge Ram 1500 5.9 magnum. I know there are plenty of threads on the heat not working in these 2nd gen rams, though while trying to figure out why it’s not working I saw this:

I can’t find a very good diagram of the heater core lines, though these look backwards, and if they are backwards what would be the point of doing that, also could that be the cause of having absolutely no heat? I just got the truck about 3 weeks ago and am trying to get the heat fixed asap, this Ohio winter is sucking with no heat so far lol. It blows cold out of all vents the vent selector works, I can hear the blend door moving when having somebody change the temperature quickly (I’m not sure if I’m just hearing the actuator move or if the blend door is actually moving), after a 10 minute drive both heater core lines are about 142 degrees. Any ideas or thoughts about why the lines would be switched would be awesome thanks!

 

The blend door seals are likely shot and are allowing cold outside air to get into your heater box and into your cab, given the age of the truck. Also, what temperature thermostat do you have in your truck? It should be 192 degrees, especially in the cold winters of the Midwest.

 

Guessing t-stat is stuck open

Not sure it would matter if lines were reversed at core

 

Doesn't matter. The blend door isn't the recirculate door. That's the one that switches outside or inside air. Even at 142* you should feel some kind of heat at the vent. If you feel nothing i would remove the blend door motor and see if the blend door is intact and working. Inspect the coupler between the two, It fails a lot. You can run the truck and manually turn the blend door, You should feel heat then.

 

Neither one of the 2nd gens I have owned have had heat worth a darn... Heater core is the highest point in the cooling system, and trying to bleed all the air out of it is an exercise. In the truly cold weather, I can't turn my fan on high, as the air flows to quickly thru the core, and barely warms up....... Fortunately, I don't have to drive far.

 

We get good heat outta my non-profit's '98 1500 5.9. Colorado cold isn't Michigan cold (no humidity), but it's still cold.

I'll be working on a '98 V10 soon so will see how heat is there.

Note RA now sells Calorstat. Just put one in a '99 XJ 4.0 (same t-stat as Magnums). Seemed like a quality piece. Don't bother with Motorad/Stant. Have been told OEM Mopar is now Motorad, too, but cannot personally verify.

I'd see what the ECM thinks coolant temp is. If you're not getting 190+ the engine simply isn't getting warm enough

 

Furthermore, you should note a disparity between hoses if the problem is in the core (blocked).

If BOTH hoses are 142, lukewarm coolant is going in and coming out -- that ain't the core's fault.

I worked on a '00 1500 that was just barely warm-ish at the vents and it was hitting 170 coolant temp (t-stat stuck open). Honestly at 142 I don't know if you could expect to feel much of anything on a cold day.

 

Oh and apparently it would seem I wanna pad my post count (not really): get a thermometer to drop in the center vents. No different than checking a/c performance. Then you can have some hard data.

You might be surprised what human perception does to lukewarm air on a COLD day -- it may seem not warm at all.

The vent 'stats are cheap. Could even use a meat thermometer-- don't tell the wife (kinda like when you borrow the turkey baster to extract vehicle fluids)

 

I'm gradually doing a complete rebuild on a 2nd gen HVAC box as we speak. Replacing the heater core, evaporator, doors and insulation. We shall see if we get good heat out of it once the swap out is done.

 

I'll be curious to see your results. I would LOVE to actually be WARM in my truck on those cold winter days. If I drive far enough, the heater actually starts working decent, but, I am not about to drive 100 miles to work, just to be warm when I get there. (it's 7 miles to work, it's just getting comfortable in the truck when I hit town....)