Another HVAC Question

[mikemileski]

My truck is a '72 GMC 4x4 with factory AC. Right now the vacuum hose that leads to the heater control valve has vacuum to it all the time, regardless of whether the control lever is moved to the hot or cold position. The heater valve that's on there now is the type that's open when no vacuum is applied, which means it's closed continuously for me because my system is applying vacuum to it at all times. Does this mean that my vacuum switch is malfunctioning? I have a two port system and the vacuum hoses are plumbed exactly as the diagram for the two port system shows in the service manual. If the control head vacuum switch is bad, is it a separate piece or would I need to buy the entire assembly (and, if so, who makes something that's a higher quality than some of the cheapo replacements I've read about)? Also, is there anybody in Tucson that has some knowledge and experience with this?

Mike Mileski
Tucson, AZ