Chevrolet Van Heater Control Valve

I Think This The Correct Name For This Valve.....it's A Diaphram Valve With A Vacuum Line Control That Has In/out 1/2" Heater Hoses, But It...

Raidiator Hoses Collapsing No Flow From Hoses It Seems 91 Chevy Vandura 3/4 Ton Van V6 When I Turn On Heater Blows Hot Air But Then Hoses...