Because the heat in the front doesn't work the windshield does not defrost, and even when i have the it on defrost only cold air is coming out of the other vents, so I have cold air blowing on me when it is 0 degrees outside. Thankfully the heat in the back works bc it keeps my 4 month old son warm. But I still need to fix this problem, but friends that work on cars don't know what is wrong and i can't afford to take it in to get looked at/fix. Hope its something simple and cheep. PLEASE HELP!!!

Rear heater works great!! Front heater, on every setting may blow warm when vehicle is under load but other than that it is always cool. I checked coolant level, bled the system, cleaned the cabin filters. I have great air flow but no heat at the front. I drive uphill for half an hour and it is warm air but not hot. As soon as I head down hill the thermostat drops in temperature and blows cool air. Intake manifold gasket was replaced a couple of years ago and no external leaks can be found. Any good ideas what to check next? Is there a component that allows the hot water into the heater core? I need help!!