In preparation of wiring a hot tub I took off my breaker box panel face plate and noticed that the 8-2 w/g white romex coming into my breaker box had the bare ground wire connected to the neutral bus. The other two hot wires go to the 30 amp breaker. This romex comes from my air cond compressor unit outside and was installed by a local company.
I do have an separate ground bus in the breaker box and all the other grounds are attached there. All of the neutral (white) wires are attached to the neutral bus except for this lone bare ground wire.

My breaker box in the garage has no "main" breaker switches in it. I have a box with two breaker switches in it located next to my electric meter outside, which I guess that is my main service box. I have no subpanels.

For all these years it has been connected this way I have not experienced any problems. The house was built in 1972 with the main power wires and the 220v appliance wires made of aluminum and the smaller 12 and 14 ga wires of copper.

My question is this:
Is it proper for this ground wire from my ac to be attached to the neutral bus or should it be disconnected and re-connected to the ground bus?

I've tried calling the A/C-Heating company that wired it to ask this quesiton but they have so far not called me back.

Thanks in advace.