I have a 94 civic coupe ex. Everything works fine, except in the winter time I am simply not getting enough heat. It takes a long time (more than 15 minutes of driving) before I start getting any heat at all, and when I do, it is lukewarm and basically I have to keep the heat all the way up with the fan on max in order to stay comfortable.
The first thing I did is replace the thermostat and check the valve with the little wire attached which goes to the heat control on the dash. The valve is fully open and seems to be working fine. I even flushed the entire cooling system several times, thinking that maybe the heater core was clogged or something, but it seemed to flush just fine as well.
A mechanic told me that it might be the dampers inside the dash which make the air go through the heater core instead of coming in directly from the outside, but I have no idea how to check those. The air conditioning doesn't seem to be quite as cool as it could be, which makes me think that may be the problem.
Does anybody have any tips on how I can go about this? Do I need to tear apart the dash, or is there any easier way to try to make it work, like going through the vents?

 

Check the coolant level in the radiator. It needs to be completely full. So the engine does warm up to normal temperature, like halfway up the gauge, yet you still get little heat?

The heater air door is controlled by a mechanism which you can see on the bottom of the heater box, right in the center of the car. When you move the dash lever to hot, a cable moves this mechanism which pushes the door open to the heater core, and also the mechanism activates another cable that opens the water valve under the hood. The valve shuld move fully from closed to open as you move the lever from cold to hot.

Even if the valve opens, the core could be blocked. Did you flush water directly through the core and valve?

 

The engine does warm up to normal temperature, albeit I think it gets there slower than it should. However, even at normal temperature, the heat coming out of the vents is still lukewarm. There is enough coolant in the radiator.
I haven't seen the heater air door. Is it possible to take off one of the vent grilles to see it better? Otherwise, I will try to get a small gooseneck light so that I can snake it through the grille at night and maybe see if that heater door which you speak of is opening.
The water valve under the hood is working fine. I disconnected the hose which plugs directly into the valve and flushed water and air through it and through the heater core. Water went through fine; there didn't seem to be any blockage.

 

Is it possible that the HVAC air flow system (blower, evaporator, heater core) is clogged with leaves and debris accumulated over time? Start by removing the blower motor (three screws below glove box)) and checking for leaves there.

 

Mine had alot of leaves and junk in there. You could have some blocking the door from closing. Are you trying to use the recirculation too? Cause if not- your probably getting outside air too.....

 

it is possible that the cable that goes from the temperature slider to the heater valve has come off its tab on either end of the line, causing the temperature slider to result in no change in temperature.
if it for example came off its tab thing whenever you were sliding the slider, and it came off at the halfway point, your heater valve would be constantly stuck at the halfway point, letting less radiator fluid through the valve than there would be if the valve was fully open

just a possibility, happened to me