The vehicle is a 2000 V70XC, 146,000 miles. Last night I discovered that I have hot air only from the driver's side vents, the passenger' side is cold. Playing around with the controls it appears that air positions are switching on both sides correctly using the center ****, there is just no heat on the passenger side. I popped the climate control unit out and opened it up to have a look. While it was apart I ohmed the left and right pots. I don't know what the values are supposed to be but both pots were giving me similar numbers on both ends of their ranges, so they seem to compare favorably.

What else is there to check? There must be temp sensors somewhere? What physically controls the temps side to side, a door or a valve? I suspect that I had the same problem with the AC this summer, but I just got the car and didn't travel with a passenger during the hot months.
Thanks

 

I just checked and I am getting the ECC fault from the flashing leds on the RECIRCULATION and AC OFF buttons.

 

There is a motor that controls the passenger side for heat and A/C.
If you remove the glovebox insert you should be able to see it off to the left looking into the glovebox.

 

Yep, it was the air flap actuator, passenger's side. Thanks Tech. $15 used from the local salvage yard.

 

Glad it was an easy and cheaper fix!!