When you say the fuse is blowing, it immediately makes me thing there is a problem with the blend door actuator. The blend door is responsible for determining if you get heat or AC into the vehicle. It is located near the heater core. In one position, it allows ac to enter the vehicle, and in the other position, it allows heat to enter the vehicle. If it is stuck, you won't get good heat if any at all. There are some other things you could check before that. However, I mention it first because of the fuse issue. Also, check to make sure the engine coolant is full. If it is low, it will cause an issue with the heater. Also, make sure the engine is warming up to normal operating temp in a reasonable amount of time. If it doesn't fully warm up, replace the thermostat. If that isn't a problem, check this. Start the engine, allow it to warm up, have the heater on high. When it reached normal temp, feel both heater core hoses. If both are hot, then you are getting a good flow through the heater core. That would then tell me the blend door is an issue. However, if only one hose is hot and the other slightly warm, chances are you have a plugged heater core. Remove both heater core hoses (when the engine is cold). Take a garden hose and blow pressure through both hoses. One way is the normal flow direction and the other is called back flushing. If a lot of junk and rust comes out, reconnect everything and refill the coolant. If you plug the hoses to the engine / waterpump, you will loose very little coolant. God knows how expensive it has become. Regardless, if the heater core was plugged, that should take care of the problem. If you are unable to get coolant to flow through freely, the core may need replaced.
Friday, January 14th, 2011 AT 1:46 AM