I just had my ac install in my 96 Chevy Tahoe, the ac runs great. Until, I accelerate or go up a incline. Then the ac starts blowing heat, until I level out. It does fine on cruise or just running around the city, it good and cold. I was wondering if there is something slipping, the fan clutch going out, the valve on the right side that goes to the heater core inside my ac unit bad. Someone please help.........................