Quoted from source:
"Check your hoses, and check your heater core.
The heater core is under the dash. Have you
smelled a coolant odor in your cabin ever?
there is a valve under your van that regulates
the rear heat. this is a common problem.
Inspect the 2 vacuum lines that run from the
fire wall down to the valve. Lots of times they
will rot and cause the valve to stay closed.
you have 2 heater cores the second behind
driver seat on wall behind plastic panels my
friends just went bad. he had no heat wet
carpet he said under 1 hour to have it fixed. (sic)"