How does a heater system work? Anyone have any diagrams?

On my 99 ctd:
I have vacuum controlled air exchange, and that's working, so I can switch from defrost to vents to floor.

I have blower motor control so I can control fan speed.

I don't have temperature control. It's stuck on cold. The switch works, it's just a big potentiometer. The signal gets where it's suppossed to go over under the passenger dash. Turning the **** changes the signal, but it doesn't affect the heater system in any way.

So, I don't know exactly what part it is that I need, and I don't understand how a heater system changes the temperature of the air coming out of the vents. So please help me on either front. I'm thinking what I need is the heater valve actuator, but I'd like to know how the actuator and heater valve work.

 

Well, I ain't the most knowledgable DF member around and don't have any diagraoms I can send but I'll give it a try. On the '01 which is the same as the '00 and probably the '99 I assume the heat and a/c mix is controlled by a blend air door, which regulates the proportion of heated air to cooled or outside air. the a/c runs of course when switched on but the heater core always has hot water circulating through it. So there are probably two areas to check. One is to check to see if the blend air door motor is operating. If it is not then it could be in the cold air only position. If the mototr is o.k. and the blend door is opening and closing then check to see if the heater core is getting hot. If not the core may be plugged. The easiest way to check this may be to see if the hoses going into and exiting the heater core inside the engine compartment are both warm/hot. If there is no flow the hoses would never heat up. This is probably the first thing I would check.

Sorry I could not be more descriptive or have any visuals references to share. Good luck.

 

Another thing that can stop the flow threw the heater core, is a bad water pump. Does the truck's water temp get hot? Have you checked your water level?

 

My first inclination is the thermostat is bad. If it doesn't open, then no heat.