Heater blows cold air?

About a year ago the radiator and upper and lower hoses were changed along with the thermostat and a reservoir hose. I cannot remember if the heater was blowing hot air or not then, I think it was. Now A/C works fine but Heat only blows cold air from all vents. When looked into Door Actuators, I heard Right Air Temperature Actuator trying to move but sounded like it was struggling. Any suggestions on whether it is the problem (because dash has to come out in order to replace it) or where else to start digging? Thanks