I'm not sure if something like this has been posted before, but from what I've read so far I can't find any similar enough to my situation.

I have a 99 durango V8, 5.2L, 4x4. I cannot seem to get heat into the cab (there IS heat but only if you hold your hand right up next to the vent and that is just VERY minimal. 2+ inches away from the vent and it may as well be A/C its that cold). We have had it for almost 5 years and it used to get awesome heat to the point it would practically make you sweat. The engine maintains normal temp. It does not overheat, but it does heat up. It's below normal, but right now it's like 15 degrees out so I can understand that it might not get as hot. We have replaced the thermostat, and attempted to flush the radiator and heater core. I say attempted because I was told it takes about 14.3 quarts to fill the system. Either there is a lot of air in the system or something is clogged because when we ( my hubby and I) drained it, we barely got a gallon-ish out. And could never get much more than that back in (with either just water to flush, or with refilling anti-freeze). Either way, something is wrong and I figured we'd try asking someone on here to see what else we can try. When I called radiator shops to see prices for a flush, I kept getting them telling me they didn't think needing a flush was our problem. Whatever the problem is I just want it fixed(preferably as cheap as possible). Driving 45 min. to work everyday(and then back home) everyday w/ no heat SUCKS!!!!

 

To flush the heater core, did you take both hoses off and connect a garden hose to one of them? Also what is your engine temperature looking like?

 

Just went through this. Wife was complaining about no heat in her truck. After a few checks, saw coolant was bone dry. Added some and stated blowing MUCH warmer air, but still not hot. I think because I didn't fill the coolant just added 1 gallon.
Next morning wife says it's still cold air. Coolant was dry again. There was a leak which led to a whole slew of other problems.
After replacing radiator, fan clutch, and thermostat, and flushing the system you can dry your hair with the heat coming out.

 

yes both hoses were taken off and ran water through the out hose to back flush it until the water ran clear. Engine temp is a little less than halfway between the lowest (130) and the middle (210). When it's not super duper cold out, it usually runs a little more than halfway between those. It's running a bit cooler than what I'd say is "typical" but as I said before its like 15-20 degrees with single digit wind chills. I dunno it that makes a difference.

There are no leaks, and nothing is overheating so fan clutch should be fine. Thermostat has been changed, and we flushed the system last night.

When we flushed the heater core, and unclamped the hoses before attaching to garden hose, they were both bone dry, so it's as if something is clogged and not pushing anything into the heater core. It's supposed to be warmer the next couple days and the hubby is going to see if maybe there is a clog in the water pump or hoses somewhere.

 

This might help

 

I just went through something similar to this in my ram, these 5.2/5.9 are notorious for having a hard time burping the heater core. Here is a thread I started over in the ram section, useful info on Burping the heater core