Eliavalencia1

My 07 tahoe ac goes in and out. Sometimes I turn it on and the rear blower blows but the front vents are not blowing anything. But there is also times that is I turn the truck off and back on I have a 50/50 chance at having the ac kick in. There is also times that the front vents are not blowing and as I begin to drive the ac will start blowing in the front. When working it works just fine as if nothing was wrong. Could it be the vent getting stuck? Two mechanics have told me it would cost $700+ just to look at it and see what's happening. But if I can fix it I want to try it first. Idk please help.