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Q: no heat? on 1990 Pontiac Bonneville

Car is actually an 86 Parisienne,but no category here.Heater core is not clogged.Zero heat in car.Am I correct that the next possible faulty item is the vacuum controlled valve at one end of a heater hose?One hose hot, one hose cold. Thanks.
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Per the GM manual I consulted, you have no heater control vavle on this car.

If you have a hot inlet but cold outlet hose in your heater core, it has to be a restriction. You have flushed it and it is clear?
Thank you for researching.The core is clear-I disconnected the lines and attached two pieces of hose,ran a garden hose through it-AOK.The car does have a vacuum controlled valve on the manifold, to which one hose attaches.Vacuum is present when the heat is off, not there when on,so I'm assuming a stuck valve.
Update: I replaced the heat valve-problem solved.Thank you again for consulting your manual.
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