I tried using "search" but it's acting funny right now, so I'll try later

BUT....car is a 99 Civic DX.

My heat doesn't work aka no hot air. The blower motor works - blows at all settings. I just replaced thermostat and put in new coolant. Car reaches normal operating temperature, but no heat - just cold air blowing out.

I checked the fuses/relays for resistance, they seem to be okay.

Any ideas? Coolant temp sensor, etc.?

 

heater core

 

do you have the 2 hoses of water , this ones go to the cabin in located on the fire wall

 

Low coolant, air in the system, are the lines actually running to the firewall. See if the blend door works, see if the coolant valve works.

 

Check the heater control valve.

 

had the same problem in my 93 ex, i disconnected the hoses going into the heater core under the hood by the firewall, ensured the heater valve waas functioning properly then flushed the core to make sure flow was going through the core once i flushed it with the water hose i left it full and connected the hoses and topped off cooling system with coolant and it blows hot all the time now. you might have build up in the core just flush it how i did.