A/C not blowing hard (Kenworth T680)

They either forgot to plug back in wiring for the actuator or disconnected some hoses when they were replacing the actuator. If the hoses are not fully connected much of the air will not get to the vents. May also be a problem with the fan speed.
Does the air flow change locations when you go from defrost to feet to...... Does the sound of the fan speed change when you go from low to medium to high?
Sounds like another case of someone did not verify their work after the repair which would have been easy to do.

 

Old fan will often spin less but still work, till it doesn’t.

 

Are you talking about less air flow or air not as cool?

 

This is probably a stupid suggestion, but have you tried 'pushing in' the fan knob to activate the higher fan speed band? When I do this on my (newer) T680 a blue light will illuminate on the knob after pushing it, and a higher range of fan speeds will then become available.

 

Real men don't read the instruction manual.

 

Did they properly charge the A/C system and inspect for leaks?

 

If the fan doesn't blow any air out the vents on higher settings and only weakly on low the blower motor resistor might be bad. It's a cheap and easy part swap just to see.

 

It's all done by machine now. Leaks and charge.