| 78 AC vacuum leak [message #312709] |
Wed, 01 February 2017 07:19  |
C Boyd
Messages: 2629
Registered: April 2006
Karma:
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Senior Member |
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I am working on a 78 PB that has a vacuum leak and will not switch air flow from floor to vents or defrost. I can pull the vacuum connectors and apply vacuum to each diaphram and all work and hold vacuum except the blue hose going to defrost door. The defrost door has 2 hoses going in the heater box from the drivers side beside the brake booster. The book says the blue stripe hose goes to the defrost door and the yellow stripe hose goes to the defrost door bleed. This is suppose to delay the opening of the defrost door and regulates the door in one of 3 positions. The yellow hose will hold vacuum but blue hose will not. I cannot find a way to get to the defrost door vacuum module. The control panel will not hold vacuum in any position. There is also a separate vacuum switch for the heater water shutoff. The shutoff valve will hold vacuum if applied directly. I am thinking the valves are leaking. Is the valves or the rubber wafers available? How can I get to the defrost door diapharam to check. Any ideas or suggestions appreciated.
Thanks..
C. Boyd
76 Crestmont
East Tennessee
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