posting this for a friend. his wife's 99 accord is blowing cold air with the heater on. i've done a little research and it seems this could be caused by a few things. i've ruled out the heater blower motor since it is blowing air. now my two culprits i believe behind this is the heater valve stuck or the thermostat. any input would be appreciated.

 

bump. also reading heating core element may be the cause. anybody have a diagram of the heating system?

 

Most likely if it's blowing cold air, its probably that the Heater Core is clogged. It's an easy fix for a DIY. Pretty much just take off the heater hoses and plug a water hose to one end out the heater core and turn on the water, and let it run through. A lot of gunky stuff should come out. Keep switching tubes until all clear water comes out.

But I would just get a whole coolant flush for you car. Radiator and everything. Ill try and get a diagram for you.

 

Ok well I can't find a diagram online lol But just look for 2 hoses going into the firewall. Should be side by side. Remove hoses from fire wall. DO NOT JUST PULL OFF. Break the seal on them first then pull off the hoses. Once that is done connect hose to tube coming out of firewall and flush it out.

Would be nifty to have a bucket around, don't think you want radiator fluid all over the ground.