Driver side no heat, passenger toasty

[Mau]

So my 04 TSX which I bought as a winter beater, isn't being a nice winter beater especially with the nasty cold spell we've been having this year.

Driver side vents (including the footwell) are blowing outside air in, passenger side vents are blowing nice hot air.

I have done the following;

-replaced thermostat (replaced with honda type 2 coolant as well)
-replaced heater core control valve
-reverse flushed with regular garden hose/water pressure
-checked the driver side air mix motor (functioning well)

What can it be ?

 

[901Memphis]

If any side or setting is blowing hot air its a blend door problem.

 

[beast3300]

Heater core is clogged would be the only thing left.

 

[GutsyGecko]

Blend door issue.

 

[Merkava_4]

Blend door actuator.

 

[toneydoc]

Some door or switch must be frozen or stuck or broken allowing outside air into the system. Look at the vents and how it brings in outside air.

 

[demarpaint]

If it isn't the blend door or the actuator that operates it, it is probably a partially plugged heater core. Google citric acid flush and try that, then flush with the hose in both directions again and see what happens.

 

[zzyzzx]

I also think it's a blend door issue.