The rear heater blows only cold air for our 03 Chevy Venture. I have flushed the heater core and it is clear. The front heating system works fine. Any ideas

Somethig is preventing coolant flow from the front plumbing "T" to the rear heater core.

I have the same problem with my 01 venture. I had someone look at it, and after deciding that coolant was getting back to the rear, they tore the panel off of the back drivers side and saw that there is a switch back there that moves when we change our setting from Cold to hot. That switch was broken and was staying on the cold setting. I haven't had mine replaced yet, but at least I know it isn't a big deal.

I have the exact opposite problem. Our rear heat works but no heat from the front on our 1999 Chev Venture. Any ideas