Hi,

I have a question about the Scion heating system. Do any of you know if there is a heater control valve in the Scions? I am asking because I can feel the air coming out from the vents is much warmer than outside air (A/C is off, fresh air), especially when car speed is low (less fresh air flow) and I suspect the heater is "on" even though the temp knob is dialed all the way to blue. I checked the engine coolant hoses going in and out of the firewall and don't seem to find the valve, which seem to exist in the hood of many other car models.

In other cars, to control heat is by adjust the flapper of the heater core and also adjusting the heated coolant flow to the heater core by this control valve. But if the Scions don't have the control over the coolant flow, it may have more heat coming into the cabin because the flapper may still leak warm air through.

I don't know if it could also explain why the A/C is not working that well because of blending with this warm air

We were having a discussion about this and came to the same conclusion, but I'm waiting to purchase a copy of the service manuals to see how the heater core in this thing is plumbed out. But basically that flapper valve regulating engine heated coolant may be allowing fluid to flow through, like you supposed. It would make sense and explain the less than optimal A/C some have experienced (I don't use mine much, being in the Bay area doesn't really call for it all that often)