A hose might be clogged or collapsed
Turn car on let run 10 minutes, gently more heat controls to various positions, use recirculate if available, do you feel heat in top, med or low vents?
Do you hear baffles moving? If those are stuck in one position that can cause all or no heat, in your case it would be stuck to all fresh air.
If so that can be a baffle motor or the control unit has a problem.
Best of luck.
It is called a gate. And it connects to one of the 1 inch hoses in the engine compartment. There is this thing on it (made of metal or made of plastic) which has a wire hook to it. It opens the flow of hot coolant to the heater core.
Sometimes these steel wires become unhooked or the "arm" which is suppose to be part of the gate is broken off. Either go to parts store like NAPA or LORDCO or other and ask in automotive. Hell, ask them to fix it at Wal-Mart. Not rocket science. Half hour tops. And a $15 part(guessing high)
Only a professional mechanic can make an evaluation as to what is wrong and as to what is needed for the car to work. YOU assume the heater is bad. I can ASSUME the thermostat has failed in the open position, as intended, and the engine is running cold. I can assume a control unit is bad. I can assume a sensor is bad. I can assume six more different scenarios. Kids on this forum guess and make things MORE expensive than needed. NO GUESSING is allowed as to car repairs. Go find a mechanic. It is the cheapest way to fix a car.
Check the temperature of the hoses going to the heater core. If they are hot obviously it is a problem with a air diverter door or its position control.
Good thing- it's hot outside.
I have a 2002 Mercury Grand Marquis LS. a/c is cold. Unfortunately so is the heat. Coolant level is good. No leaks and car does not overheat. Sorry I may seem ignorant. I know very little about cars, so these are the only things I know to take notice of. Any ideas?
