No heat help

[cre]

I can't give you a detailed explanation of every part, I don't have an assembly to look at right now. The servo controls an air mixer; A flap which opens to allow air to flow through the heater core or closes to prevent it from flowing through it to a large degree.... This is how you can have the A/C on and still have coolant running through the heater core. The heater control valve which diverts coolant in the engine bay does open while the A/C is operating, just not when it's on high. So, no heat = blocked heater core, bad coolant valve or bad VSV in the heater control assembly, bad climate control unit, bad thermistor in the heater core, bad servo or stuck mixer.

I'm going off memory here so if I'm slightly off on something it's because I haven't worked on one in quite a while.

Originally Posted by interested!

Questions? : how do I test the servo to operate to open the door to hot air?

See the like I've already posted for diagnostic procedures.

The heater control valve's (HCV aka heater bypass valve) VSV is the most common point of failure.