No heat

The smell and vapor on the windshield and the loose of coolant is an indication of a heater core failure I would have the heater core checked also check the coolant lines under hood by the firewall they rust and leak coolant,

This guide can help

https://www.2carpros.com/articles/car-heater-not-working

When you say temp drop all the way down and goes back up that s make me think of the thermostat
but u said it was replaced
check coolant level
run and warm engine open hood and

Check heater core hoses if both are hot, if not the heater core need to be flushed as a 1st step
these are the steps
Warning: never remove the pressure relief cap under any conditions while the engine is operating. Failure to follow these instructions could result in damage to the cooling system or engine and/or personal injury. To avoid having scalding hot coolant or steam blow out of the cooling system or degas bottle, use extreme care when removing the pressure relief cap from a hot cooling system or degas bottle. Wait until the engine has cooled, then wrap a thick cloth around the pressure relief cap and turn it slowly until pressure begins to release. Step back while the pressure is released from the cooling system. When certain all pressure has been released, press down on the pressure cap (still with a cloth), turn and remove pressure relief cap.
Engine cool lower the coolant level
Locate the two hoses running to the heater core
disconnect them at the engine side leaving hoses connected to heater core throw the firewall
use garden water hose and compressed air if possible
run the water and follow by air throw one side and out the other and vice versa
do that two to three times watching what leaving the heater core you are looking for the good flow and clear water to run throw
reconnect hoses
top off coolant system
good luck
let me know

Do you mean you have air coming out of the dash but it doesn't get hot eventhough your heat is on, or you don't have air coming out at all?

Check fuses
Suspect blower motor

Low coolant level, clogged heater core, bad water pump, common issue, or blown head gasket from overheating

Roy