We have a '94 Aerbus on a Ford chassis. When using the automotive AC and pulling long grades the vacuum pressure is inadequate to hold the heating/AC bafflle doors in the cooling position. Not a problem in winter, but when it's hot that's a different story. I want to install an auxiliry vacuum pump to assist the manifold vacuum. My problem is I haven't been able to locate a supplier. Does anyone have a suggestion where I might find one :question: :question: