Just purchased a 2009 Sierra 2500HD, soon realized I had cold air blowing on passenger side with the heat on. Drivers side blows nice and hot. I'm assuming I have ...

Just purchased a 2009 Sierra 2500HD, soon realized I had cold air blowing on passenger side with the heat on. Drivers side blows nice and hot. I'm assuming I have a bad actuator. I did the HVAC fuse reset and it fixed the problem for a while, but now it is back and want to get it fixed right.

Blows cold no matter what, vent, floor or defrost.

Have looked at the parts and found that there are a few different part numbers available. Can someone tell me which actuator or actuators I need. And the location of them in the cab. Have a mechanic that works for me, that will do the work, I just was wanting to get the right part(s) and be able to point him in the general direction when he tears into the dash.