heat/cooling issues
 

My 78 blows air temperature air no matter what the temperature switch is set at. Blows hot air in the summer, and cold air in the winter, no matter what. What could possibly be wrong with it and what would it take to fix it so it functions properly? Since Im going to be driving my truck all summer, I dont want it to blow hot air when its not even set on hot. Also, I do not have air conditioning if that helps.

Lastly, in a previous thread, I heard that the only way the fan can be shut all the way off is by cutting one of the wires to the fan speed switch, which wire is the one that goes to the lowest power on a 3 speed switch?

Re: heat/cooling issues
 

Is the valve to your heater core moving when you adjust the temp? The only other things coming to mind are low coolant or a bypassed core.

Re: heat/cooling issues
 

Also, check the main blend door threaded rod holder-if it breaks, the door it always open which prevents the air from moving through the various vent settings. And yes, the low speed is always on with key on....you have to cut and cap that lead.

Re: heat/cooling issues
 

When I adjust the temp, I hear a "thump" sound coming from inside the dash, so im guessing it is doing something. Last I checked, the radiator is topped off on coolant, and no clue if the core has been bypassed or not.