I have a 1999 Chrysler Concorde LHS and the heat has stopped working. Blower and ac work fine. What could cause the heat to stop getting warm... thermostat, heater coil? Thanks

 

could be several things...based on the information you provided it is impossible to diagnose.

1)Doesthe temperature gage appear to me reading normal (as in prior to the heat not working)? If yes, then it's safe to rule out the thermostat for now.
2)Is the coolant level / mixture correct? No or low coolant can cause heating/cooling issues.
3)Is the ATC unit functioning properly? Try going from LOW to HI and see if there is a change in the temperature (when the engine has been warmed up). Also, run the diagnostic test on the ATC unit (there are descriptions on how to do this on previous posts)
4)Are the mode/blend doors functioning?These are behind the dash along thefirewall...youshould be able to hear themmoving when you change modes and temperatures.

I had a faulty blend dooraccuator last year that caused me to have no heat...the accuator is the little motor than turnsthe doors to let hot/cool air in.Not that hard to do yourself, but kinda tight area to work in...I paid a local mechanic aroung $120 todiagnose/repair the problem.

 

This was my problem. I have a leak in my system somewhere so when my "hot air" gets cold, I have to refill my coolant. Another symptom of this problem is the heat only pushes when the car is moving. Have you noticed the heat working while on the road, but cold when at a stop light or when sitting idle?

 

the most likey cause of it not working at idle is that there is air in the system...it need to be "burped"...I had the same problem on my Eclipse.