I have had two cars brought to me that blew warm (actually HOT) air no matter what. The first was a sluggish duovalve, the owner simply replaced it and did not want to "mess with cleaning a bad one".

The second was super easy - I had no power to the center pin on the duovalve. SOMEWHERE, this wire went open and the valve had no power - when it has no power, it defaults to full open which means full coolant flow to both sides of the heater core. Tearing into the harness to find the 'open' was going to take a long time, so I cut the wire near the valve, and ran a new wire from the center pin of the duovalve to the driver's side fuse box and tapped the output of fuse 15. Problem solved in 20 minutes.

Your problem 1:
REMEMBER:
Center pin must be 12 volts at all times, including when key is off.
Each outer pin feeds 1/2 the valve, one half is driver side vents, one half is passenger side vents.
Outer two pins must be at near zero volts to engage the valves and cut off coolant flow to provide for cold air
Outer two pins will be near 12 volts for warm air.
The outer pins get pulses that vary in width, the wider the time they are at zero, the cooler the air will be - but your digital meter will probably smooth these pulses and give you an average voltage reading, such that a voltage near zero = cool air and a voltage nearer to 12 volts = warm air.

The pulses come from the climate control module. If you have 12 volts on all three pins, the issue is in the climate control. If you have zero on all three pins, you have no power to the valve from fuse 15.

Problem 2:
The potentiometer in your climate control is bad - common issue. YOu can mail me the module and for $60 I will fix it and mail it back to you. DO NOT pull the module from the car until you and I talk, there are a few cautions we must discuss, or you will hate yourself when you try to put it back.