1996 Chevy Tahoe Hwhere are the vaccum lines for the heater

My heater core,thermostat and hoses and fluidsed or how can I ru are up to par.but I still get cold air from my heater! No matter what the air is barley warm and not enough to ride in the truck with my family!but I just bought the truck and that's how the heat was and I notice there were no vaccum lines going to the heater control valve!coul you tell me where are they located or how I could run some?thank you so much!