Vacuum Leak on Control Head Switch?

[mikemileski]

I purchased a '72 GMC 4x4 about six months ago that has factory air. My truck has the three port vacuum head on the contol unit in the dash and I noticed that one of the ports was missing a vacuum line. Using the diagrams I found on this forum, I installed all new vacuum hoses on the main vacuum cannister, the other two vacuum canisters that control the vents and the hot water control valve. Everything was replaced. I wanted things fixed before getting the system charged. After doing this, there is now an audible vacuum leak right at the control unit. That seems to be the only place that's leaking, all the other connections seem to be fine. Is my fix to simply get a new control unit and hook it up? Is it common for this part to fail like this? If I need to order a new one, any suggestions on who sells a good quality unit? Thanks for any help.

Mike Mileski
Tucson, AZ

[leddzepp]

Cap off the third port, it is not needed.

[mikemileski]

Would "capping off the third port" stop my leak? First, I'd have to replumb it as a 2 port system because a 2 port is plumbed differently than a 3 port system. But, if it really was that simple, wouldn't it mean that all 3 ports are on the same common plenum and it would still be leaking? I'm just wondering if it's common for the control unit to develop a vacuum leak and, if so, where might I go to get a quality replacement. I know lots of places sell replacements but does someone sell a higher quality part?

Mike Mileski
Tucson, AZ

[leddzepp]

Your question was not clear to me...I have a 3 port system and I ran it like the 2 port system. The 3 port has one input (source) and two output ports. I capped off one of the output ports and routed it as a 2 port system, much simpler. From your question I was thinking you just left the third port uncapped and followed the 2 port diagram. Sounds like you need a new vacuum switch.