1990 Ford Areostar 3L V6, Heater Is Blowing Cold Air

About 6 months ago the heater core went in my van. I replaced it and about 3 months later the rad went. I replaced it and the thermostat at the same
time. About 2 weeks ago I stopped getting heat. When you move the heat controls up and down you can hear the baffle/flap move inside the heater box so nothing seems to be stuck. I was told there may be an airlock. I'm not sure and I am not sure how to fix it.
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One check would be to run the heater then feel the heater hoses and see if they are hot. If not, you might check the vacuum line connections on any vacuum-controlled valve. If the connection is OK, pull the vacuum line off and see if turning the heater on and off creates and releases any suction in the line.

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With ENGINE cold, open the rad cap... if the coolant is not up to the neck, you need to purge the air from your system. This means that your rad cap must be in good shape and you should see added coolant disappear from the coolant bottle over several trips. Likewise with engine warm you should see coolant in the bottle rise.
As said, elsewhere, with engine at temperature, check both source and return lines to core for heat, blower off - should both be hot.
If not, then you either have a BIG bubble trapped in the core or a plugged core. You could have a plugged core from loosened deposits... BUT:
It's MORE likely you made the mistake I did... you installed the return line (to water pump) to the core's bottom nipple.
This will allow AIR to accumulate in the core and it cant be pulled out by natural flow because it stays at the top of the core tanks... thus some of the core tubes dont get water flow. If the dont get water flow, there's no heat from those tubes in the core.
Suggest you get and install a bleeder/flush 'T' in the return line AND make sure the return line is connected to top nipple.
--
Yeh, I'm a Krusty old Geezer, staving off dementia here..DEAL with it!

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