I got a 95 XJ and it only blows heat through the defrost vents...ive heard this could be due to a vacuum problem but there so many of those little valves on there i wouldnt know where to start...then someone told me there is a valve that controls water flow to the heater core is this true? and if so where is that valve located?..it takes forever to warm up and when it does its because ive let it idle forever. It will blow warm air through defrost vents when it gets warm but when i get going down the road it cools off and starts blowing cold air again....is something wrong or is this normal? (im talking about the cooling down and blowing cold air thing). any help appreciated

 

Only blowing through the defrost IS a vacuum problem. There is a black plastic tank behind the front fender. This is the vacuum reservoir. Make sure it's intact. Then check the vacuum lines running from the reservoir to the intake manifold (vacuum source) and the heater controls. See pic below.

And Yes, there is a heater control valve located in the heater hoses near the heater core. It also has a vacuum line connected. When you select heat, it directs coolant into the core. When you turn the heat off, it bypasses the core.

Start there since these are a bit easier to access.

 

x2, this sounds like a vacuum issue. No vacuum would also cause the heater control valve to not open a well.