Chevrolet Repair: 89 Silverado weak heater, heater settings, heater core

Question
Air is only lukewarm coming out of the heater.  I've opened up the housing and verified that the heater core is getting hot.  The cold air seems to overpower it on anything but a low fan.

I notice that the flap by the fan that controls whether it blows outside air or recirc always sets to outside as soon as I turn on the ignition and just stays that way.  I don't see any way to control it from the heater settings.  Is it supposed to do this?  If not, what's the most likely fix?

Answer
Hi Jim...there should be a button to turn from recir to outside air....check to see if core is plugged...is the intire surface hot or just warm...it should get hot enough that you can hardley touch....if not real hot replace the core...hope this helps