Help! I've got no heat. Air flow is good, slightly less when temp switch is in 'hot'. Coolant flow is good, but I can't get to duct where door is to check operation that controls flow from heat core instead of recirc. It's a 2002 Express 3500 ext, 180k, no other prob's. Any ideas? Is Haynes or Chilton's out yet for the Express? BRRR!
First I'd run the van and the heater system long enough to get the water circulating in the engine ... (thermostat open) ... temp guage reading "something" (rather than nothing) ... the hotter the better. Then I'd check the heater core hose temperatures ... input and output. they should be easy to find under the hood, side by side, or one on top of the other, going into the firewall on the passenger side. If both are about the same temp, chances are the core's not clogged.
If you relly want to check the core, disconnect both hoses at the firewall, and hold a garden hose to one port ... it should flow out the other pretty freely.
Could have a heater control valve problem. My 95 van had to have it's heater control valve replaced ... (I did it myself) ... due to it leaking coolant. Mine was located just inches from the firewall behind the airconditioning collector canister. This may prevent flow to/from the heater core.
jay
Is your plenum valve vacuum driven or mechanical (wire) driven? Do you get heat out the defrosters?
Good diagnostics, Jay - Abemoreorless!!!
I did the core flush - clear as a bell. I guess that doesn't do it but alas - now the heat works . Then, it got warm out, I turned the temp to cool, and when it got hot a week later - I turned the temp back to hot. NO HEAT . I did the flush again (just to see if that fixed the problem as before, AND IT DID . It's the heater control valve - where's that??? How much??? How much time???
'02 one-ton no heat BRRR
. Then, it got warm out, I turned the temp to cool, and when it got hot a week later - I turned the temp back to hot. NO HEAT 
