1998 gmc jimmy the ac is ice cold and the heater is hot which tells me the blend door is working

problem 1 with everything cut off it still blows air through the vents

problem 2 can’t control the air flow it blows out of all the vents no matter what setting it is on

 

Through which air vents the air is directed is controlled by several vacuum actuated doors. It is very possible you have a vacuum leak in the hoses in the engine compartment. These hoses will rot and leak. The hoses under the dash are much more durable so it is mush less likely that the leak is there.

There are several threads on replacing these hoses including one for which there is a link in my signature (below). The thread I created on this is specifically for the Blazers with the 4-button transfer case that has the Auto-4WD option. The 3-button ones, have vacuum lines that go to the transfer case. These transfer case vacuum lines seem to be more durable. It is the ones that go from the top of the intake manifold/intake plenum to the tee to which there is a one-way valve that then supplies vacuum to the HVAC, 4WD system, and a vacuum reservoir. It is the hose to the vacuum reservoir where my hoses first broke but the others were pretty far gone too. These old hoses also will leak where they attach over the nipples because they have stretched and dried out over the years allowing air to get sucked in.

 

thank you great info now gotta find time to work on it