1999 accord no heat
I have a 99 Accord 4 cyl.auto with a/c.It loses heat when driving.Its had 3 thermostats,head gasket,timing belt,water pump,heater core and rad replaced.Head was checked for cracks & resurfaced.Water valve is good(took it off,stuck a srewdriver through & tried to move bell crank-ok)& control cable works too.I have hot air in the shop,as soon as I start driving the air gets cool then cold.The return hose from the heater gets cold and there is no coolant flow through the heater,What's wrong? What did I miss?