If there is no coolant it can’t work… Top Reasons Central Heat doesn’t Work. the ac works great nice and cold but when I switch it to heat it still blows cold. I assume the blower motor is still working, but what can be the cause of the heat going out suddenly? In most central, ducted systems, there are two distinct units which cool and heat residential homes: the air conditioning unit, which typically is placed outside, and, the furnace, which generally is located in the garage or another out-of-the-way place inside the home. AC works fine but I have no heat. it is not switching to heat. If cold air is coming out of the heating vents, even when the vehicle is warmed up and the thermostat is set to hot, you could be dealing with one of the following problems: This blog post will give you a good idea of what might be causing the problem with your car heater. Best answer for Why Does My Air And Heat In My Car Only Work Sometimes. Your car's heating system is not all that complicated. the ac works great but no heat 1 Answer. There are any number of reasons cold air or no air is coming through the vents. How the Heating System Works . Your car’s heating and cooling system uses the coolant to move heat from the engine into your car’s heater core. But today the heat seemed to stop working all together. Your engine runs by turning a mixture of fuel and air into a series of tiny explosions, so naturally, this process generates a lot of heat—so much so, that your vehicle must also have a cooling system to prevent it from overheating. Your car’s heater uses heated engine coolant to warm the air that is blown into the cabin, while the air conditioner uses a compressor driven by the engine, combined with both high pressure and low pressure lines, special refrigerant and many other components. That’s small radiator sort of thingy hidden behind the engine. It's a 2003 Saturn L300. i have a 2008 chevy cobalt. Reasons Why a Car Heater Stops Working There are a few reasons why a car heater may be on the fritz—it depends on the nature of the problem. Nothing but cold air was blowing through the vents...it never warmed up. A cold winter day is no time to find out your car heater isn’t working. I was told to check the fuse and/or check the passenger side to see if there's water ( heater coil issue) no water on floor. The air in my car hasn't worked in a couple of years but the heat always worked...very well at that. AC works fine, but when I turn the nob to red zone with the AC off I get no heat in the car. A fan blows over this heater core and the warmed air enters the cabin. Heater control valve When you set the temperature to hot, air being passed over the heater matrix should be ducted into the cabin. While both the heating and AC are connected - to an extent - within your car, they’re actually separate systems. I'm not sure what fuse is associated with the heat as its not labeled as such. 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