We have two air condition and heating furnace, I had problem with one, so I calle dfriend of mine's husband, who waorks as maintenance guy, for apt, heat and cool. He fixed the proble, but he, checked second one too. After two days, when I turn on my good ac, the furnace part is in attic, is shaking. I thought that I have halicopter on my house, and I went out to check it. But the I found out is my furnace part. Ac unit is behind the house, but the furnace part in in attic. My husband is out of town, I do not know what to do, and it is very very hot.

I can only think the motor is loose or unbalanced. You need to determine which unit first, then, if familiar with the dangers involved, watch ehrn that motor operates, you may see the problem.