Heater blows out cold air
Top up your coolant level in both the radiator and the coolant bottle. Next, I would check the thermostat or engine temperature at the thermostat housing (195-210F) with an infrared temp scan tool.
A. Coolant is a sealed contraption. That being said your coolant levels shouldn't be low unless you have a leak. B. If its blowing out cold air, does it over heat? Start with thermostat.