heater problem by a fng

[Ironmen77]

My 1990 xj only blows out the defrost vents. Is this a vaccum problem or electrical. Temp control works fine, blower runs fine. Is this a simple control replace or is there a different fix?

 

[old_man]

This is the classic failure due to a vacuum leak. The most common failure point is a hard plastic line that runs under the battery.