My 1980 300SD has been going great. The air has been working well (in Las Vegas).

I just picked the car up from a shop where I swapped some computer work for oil cooler lines, and oil change, a transmission service and motor mounts.

Now the air doesn't work. Blows cool when I am driving fast, warm air otherwise. Blows hard, just not cold.

I think they must have done something unintentionally. Can someone help me with what.