89 GMC Suburban

I have two questions one is what could be the problem with my heater it only blows cool and I have replaced the heater cors. And two is when I close my doors they never close complety I have too slaam them shut 3 or 4 time to get it shut. is it the locks????

Have you replaced the thermostat? If the thermostat sticks open and lets the coolant flow too fast you won't get the heat you so desire