Q: Motor/ Glove Compartment area is intensely shaking when i put my air at a certain point. Car does not turn off or idle.

The car has been sitting for a year I have recently gotten work done on it like a new radiator and battery I just got out of the shop today and had new hoses put on for the cooling of my car. When I was leaving I had turned on my car and put the air on to 2 which was working fine but I live in South Florida and it's 120 degrees out so I put the air up a little more and the car started lightly shaking so of course I turned it on higher curious to see what would happen and it started shaking intensely I ran back inside to ask why that was happening because it never did before and he said it was just the motor warming up since it hasn't been used in so long. So I drove home and kept the air on and the engine running for about 15 minutes total after leaving the shop but still continued to make the noise. I turned the car off tried it again 30minutes later and the noise is still happening. To me it doesn't seem normal I would just like a second opinion before I go in there raising hell

My car has 18000 miles.
My car has an automatic transmission.