If I was you I wouldn't just fix the blend door alone , replace the evap core and heater core while it's out. It's a 99, you'll be kicking yourself if you don't.

 

stumbled across this in the search. Did you ever fix the problem if so what was it? thanks

 

No amount of burping worked for me.

Try disconnecting both core hoses extend one so you can divert crap from your engine bay, like into a bucket if your environmentally friendly. Pre-treat with CLR and Water (Or I hear you can use Bleach) let sit for appropriate time, drain.

Fill core with water. Connect air hose (I used blower nozzle with restrictor/reducer removed) Set pressure to 90psi and evacuate the water in your core. Repeat until the goop stops drip out of the lower hose.

Reconnect all hosese, replace fluid, elevate front end, burp...should be good to go.... IF your core is at fault and you manage to open enough of the blockage.

Once the truck is up to operating temps, the bottom of your heater box where the core sits should be nice and warm..if not, your not getting hot water through the entire core and your heat will suck.

 

would my heater core make a sloshing sound with water at times when i take off. I dont believe its my overflow bottle. it sounds like its from the far rite side like rite near the dash. I hear a sloshing sound when i get on the gas rite away.

 

Air pocket in the heater core. I think that was standard equipment with the 2nd gens.... thoroughly burp your cooling system.

 

ok sounds good. I'm going to more then likely do this today. Had to do it on the jeep a year or to ago. probably the same heater core knowing dodge. didnt seem very effective on that but hopefully this does the trick. thanks

 

So this is one of the many threads I've found on this particular subject, but there seems to be much more going on here. Did anyone pinpoint the actual issue? I'm having this eact issue on my '98 Ram...I am just hoping that someone may have the solution.

 

Replace the heater core.

 

I suppose that one was my fault...thanks for responding zman17. The heater core is functioning. I have already replaced the thermostat, as the aftermarket one was not allowing it to reach operational temperatures. It does blow air, unfortunately it only has one temperature, which I can only describe as lukewarm. From some research that I've tracked down in the last couple of days, it appears that it may be a blend door issue? Unfortunately I've not had time to rip my dash out to inspect what is actually going on down there. Further complicating the problem is that I don't know if I'm diagnosing the faulty blend door properly. According to what I've read, you can test it by turning the temp **** from all the way cold to all the way hot and vice versa. When you do that, you should hear a clunking noise (the blend door opening/closing). I don't hear that, but I'm not sure that the '98 Rams were ever supposed to make that noise. Any input would be greatly appreciated. Thanks again for responding.

 

A 98 has a cable to operate the blend door. So you should indeed here the clunking when you turn the **** back and forth.