Could be that your front heater valve (located under the van in the spare
tire area) could not be closing all the way (control cable problem) or could
be worn out (valve problem).
Check this out and I have these parts on hand if you need them.

Thanks,
Ken Wilford
http://www.vanagain.com
John 3:16
Office (856)-765-1583
Shop (856)-327-0027
Fax   (856)-327-2242