If it's not air in the system, it could be that your heater core is
all plugged up with crud.
You really should get full heat at full fan.

I know this sounds patronizing Dan, don't hate me for it.
A lot of people don't know how to use the controls.
For best heating you should have them set...

top,    right       windshield
2nd,    right       hot
3rd,    left        feet
4th,    left        flow

A lot of people think that that flow one, bottom, should be closed off
to warm the van, but as long as your heater core is heating...

Back to Dan's heater again.  Best of luck.

Cheers

<sstones@io.org>
SStones             Toronto,  Ontario.