Heater will not blow hot air until about 20 mins. after the van has been moving

I would check the blend door actuator. If the door is open all the way, one direction, the air blows over the heater core. All the way in the other direction, the air blows over the evaporator. Anywhere in between, a blend of hot and cold for temp control. That explanation is a little simplistic. the info is for ford windstar.

fill the rad to total capacity, also your heater core is most likely "air locked" you nede to loosen the return line from the heater and with heat set to high and engine running, allow fluid to leak from the loose connection until all air bleeds out. since the heater is higher than the water pump it will not force it out on it's own. you could get a mechanic to do this for you but why waste money for a simple fix

You have an air leak. The heater should be patched for leaks. It is a home project that takes 10 min

heater will blow cold till engine warms up ??

Assuming the radiator is full of coolant, and the engine is reaching normal temp of 190 degrees, you could have a blocked heater core or the temp control valve may not be working on the heater hose.
I would check to see if both heater hoses are getting hot.

if the ac system is very strong and there a lot moisture in the air the a'c evaporator core will freeze up and stop air flow threw the cold core only use the recuiculation part to cool the car down about 5-10 min the turn the recuit off

Are you sure the relay isn't getting weak? Try swapping with another.

always check the coolant first, then feel both heater hoses to see if they are equally hot.
if one hot and one cold, then the heater core is clogged
if both hot then you have a blend door problem.
on the a/c there's some time a rear unit that blow cool air even the front does not

Need more information. The most important thing would be to watch the heater water valve move when someone turns the control from hot to cold, back and forth?
Heater valve controls tend to be operated by vacuum, and switched by a heater computer. Lots of possibilities. But first tell us what you see move when operated? Valve is usually in engine compartment, in the heater hose. Follow the hot one.

Replace the temp control on this car, it should be electrical control not cables.