heater is blowing cool and warm air not hot
my heater started acting up about 2 weeks ago. The heater would blow cool and warm air but never hot air. We took it to the dealer, they ran a pressure test. no leaks. My coolant levels are fine, my car is NOT running hot. Where do I go from here. It is a GMC acadia 46,000 miles. I dont want to start replacing things I dont have to replace. Please help!