Help me fix my heater....

WEll it was a whole 37 degrees today so i go and turn on my heater the first time this year and it blows nothing but cold air. The first initial air was luke warm but after that i might as well had the AC on does anyone know why, the water temp was 195 ish and it has a new heatercore and t stat so anyone have any ideas.
 
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start by checking the small vac line up against the firewall that extends from about the center over to the passenger's side. One may be broken or cracked an is not allowing the air handler duct to go one way or the other. The valve that opens up the water flow to the heater core may also be stuck closed. You'll need to search around for that a bit. I don't remember off the top of my head where it's located (maybe someone else will know). After that, you may need to get under the dash and check those same vac lines after they've run through the firewall. Finally, if all else fails, check the small hose in the engine compartment that runs through the firewall and feeds the heater core. There's an orifice in there that sometimes gets turned sideways if the hose is old and stretched out. The heater core itself may be gunked up with mineral deposits etc. but that's rarely the case as it requires a significant amount of buildup to keep the core from heating enough to give you warm air.
 
I'm going to go with old reliable. Check the temperature control dial for cracks or damage. Pull it off, and use a vice grips to turn the peg all the way to hot. If this works, replace your dial.

The potential reason it could be going from warm to cold is initially when you turn the vehicle on, there's warmer air left over in the vents, then once it purges all that, it blows in the cold air from outside.
 
ok well i tore into it today, i think my blower motor needs replaced it only works in high now, and everything else seems to be operation correctly, the temp cable seems to open and close the door correctly so does anyone else have any ideas?
 
id like to know also....but ive got more problems. i need to fix mine so it blows air out of the vents and not just the window defroster. got a little crazy and started takin out stuff that i thought was for the a/c unit.....now i have to figure out how to hook up the vacuum lines correctly
 
I know the Switch is bad but i need to know why it isnt blowing out warm heat when the motor is fully warm i am going to tear into it possibaly tuesday. ECU that means that the vaccume line isnt properly attached to the rest of the unit it comes out of the same area as the AC lines.
 
If it only blows on high then the resistor is more than likely the problem, not the switch. I'm not sure where it is located on the Mustang, but it is usually somewhere it can be cooled. (inside the plenum maybe?) As far as no heat, are you sure there is air blowing across the heater core? Did something like a rag get in there when you replaced it? Also check the condition of the blower fan as well.
 
Can someone give me somthing to look for when i am tearing into this? or explain how the heater works? The only thing that stumps me is if i shut it off for about 5 min and turn it back on the first intial blast is warm then it goes cold... it got up to 26 today so i couldnt work on it. I also have no clue what a resnator is.
 
Let the car warm right up and check to make sure the lines going from the engine to the heater core are nice and warm. If so, that means it is something inside the car because there is coolant circulating through the core. If not, then it is something under the hood. Make sure the coolant is full also.