I have no heat in my 1998 dodge durango it blows cold air i change threm and flush

there could be a air lock in the cooling system and the heater core is full of air
bleed the air out or have an accredited radiator shop do it
make sure that the heater control valve is getting the signal ( cable, vacuum etc ) from the heater control switch ( climate control module) to turn the coolant system on to the heater core

sounds like you need more antifreeze , make sure fluid is at proper line on overflow tank

Check hoses to heater core to make sure BOTH are getting hot. If yes, bad blend air door or actuator likely. If no, back flush heater core or replace.

most likely your controls are bad or a vacuum leak in dash

Have you bled all the air out of the system? Assuming you have, I'm thinking you've still got a major blockage or more likely, because there's no pressure, you've got a bad water pump. The impeller can corrode or fail without actually leaking. There is also a shut off valve on the heater hose which may account for the lack of heat but not for the lack of pressure. I'd start with that and continue on. Please let me know how this worked and if I can help more if the problem persists. Thanks and good luck!

Most newer vehicles hav a motor controlled damper door to change from cold to heat or vice versa. Could be bad motor or controller.

The heater core might need back flushed, I just did mine this winter. Go to dakota-durango.com and introduce your self and your rare as ever truck, a v6 durango, and have fun.

The blower has debris in it. It need to be remove and clean out. How do you remove the dash board. See no screws.

The problem that has caused this cold air only issue is the Air Temerture Control Blend Door Actuator Motor, this motor is on the ouside of the air duct about center of the dash, in order to access and replace it u must remove the entire dash assembly. this is about a 12-15 hour job.

Thats because the air duct has a hole in it that is allowing outside air to low through it.