Dry run hot for awhile and next time I use it it blows cold air.

Sounds like the thermostat is stuck open or low anti freeze

It could be going out on a high head pressure safety

It has air in the line. let ir idle with the radiator cap off for a little while and the air will work its way out. You may have bigger issues, but I do not think you need to clean heater core because you get heat sometimes. Do you see a lot of bubbles when you take the radiator cap off when running, head gasket if so.. You can take the cap loose while the engine is running, but not after you stop it, it will be to hot. Good luck

Sounds like a bimetal over temp cutout is faulty.Usually about 30mmx20mm in size with 2 wires.Cuts out when heater exceeds a certian temp.

Sounds like the coil is freezing up either because of lack of air flow over the coil (dirty) or because of low charge.

do you have an automatic change over thermostat? this would switch it from heating to cooling.

You have still got air in the system.Remove the Feed back pipe from the header tank and wait for all the air to come out while the engine is running making sure you are toping up the header tank at the same time Dont allow header tank to run dry while doing this.Good luck

Ya I would almost guarantee you that the radiator is shot.
You will need a new one.
Cost 800.00 to 1100.00 to get a mechanic to install.
You can buy one your self for about 300.00.
Do it yourself.
to test if that's the problem try this.
Fill the radiator all the way to the top with coolant
Run the van till its warm check hoses to feel for heat.
If its all hot and good..then id say you got awhile before you will need a radiator.
What will happen next is your van will start to over heat when you least expect it to.
Good luck

sounds like the sytem is freezing up have pressure switch checked

Had the same problem with my Mazda6 awhile back. Took it to the dealer and they found the radiator wasn't holding pressure. They replaced the whole radiator under warranty (WHEW!). Not sure how to check for that kind of thing, but it's a start.