2006 Legacy hot air on driver side, cold air on passenger side.

[Pinegrovesubaru]

2006 Legacy 2006 heater works great on the drivers side, but only blows cold air on the passenger side. The same situation happens in the defrost mode (hot air out of the left vent, cold air out of the right vent). The quantity of air varies with the fan speed, but the air is dead cold on the passenger side.
I looked under the dash and behind the glove compartment and found nothing.
I removed the center counsel to get a better look at everything.
The motor that moves the damper between vent, heat, and defrost is working properly.
The recirculate/fresh air motor and damper are working properly.
The linkage for the cold to warm adjuster is working properly.
I couldn't look into the air ducts to see the heater coil but I tried.
Having everything apart confirms the left duct is hot, the left-middle duct is warm, the right-middle duct is cool, and the right duct is cold.
I can't imagine the right side of the coil is blocked and the left side is open, but that is how it is acting.
Any suggestions as to how to get to the hot water coil to inspect it?
What boggles my mind is that the quantity of the air is the same all the way across the four ducts, but the air goes from warm on the left to dead cold on the right.
Thank you for any ideas that you have.