Kevin_646

I’m having the problem of: No heat, and would like to ask for some troubleshooting help.

The heater blows lukewarm air.

When I turn the temperature control to cold, it blows cold air.
When I turn it the control to hot, it blows lukewarm air, there is a noticeable difference, but it’s not as hot as it should be.

Question: Do you think the problem is a clogged heater core, with this symptom?
or is it more likely to be the “blend door”?

Driving the car, the temperature gauge is steady, it never overheats
The radiator stays full, so I know there is no water leak.

I’m trying to figure out if I should flush the heater core, or figure out the blend door.

It’s a 2003 Civic LX

Thanks for your help,
Kevin

ezone

Head gasket.



Blows lukewarm air....at idle. Does it get hotter as you drive and have the engine revved up?
Airlocked heater core....caused by coolant loss or head gasket leak. Yes the radiator may appear full even though the core has air in it.
Burp out the heater system and see if that helps the heat, then expect to do a head gasket if it did.


Inspect the action of the water valve in the engine compartment on the heater hose. If the cable moves the arm fully (about 90 degrees from full cold to full hot), the blend door should be working correctly.

Seriously, I see almost no issues here with cores and controls. Almost all heater complaints I get to see in my little area here are caused by the blown head gasket.

I've seen a couple of the water valves trashed though, the arm moves ok but the valve inside did not.

Kevin_646

Good news, I figured out part of it!

First, a little background, I figured out how this works, in case this is helpful to others with this problem:

There is an “Air Mix Control Motor.” This motor pushes open and closes the “Air Mix Control DOOR”

The Air Mix Control Motor is inside the cabin, above the gas pedal. If you lay on your back, floor, drivers side, with a flashlight and turn the control from hot to cold, you can see the motor moving.

It pushes a cable, which pushes the "Door." The Air Mix Control Door is in the engine compartment. This door or valve is in the coolant hose, close to the firewall, going to the heater core. On mine, it’s a blue cable. (Maybe these were formerly called “Blend Door.”)
When you turn your heater control to HOT, the motor turns, pushes the valve, in the heater/coolant hose, all the way open, so more hot water can go into the heater core. (I think)

Back to my problem, I laid on my back, watched the motor push the cable. But it didn’t push it all the way. So I helped it. I pushed it the last 1/4 inch, with my finger. AND THAT DID IT! Hot air now comes out my heater.

So I found the problem, it’s in the motor or door, not the heater core, or anything else.

But it’s not really fixed, because when I turn it to cool, then back to hot, the motor still doesn’t push it the last quarter inch, unless I help.

Based on that description, I’m thinking the problem is that the door is binding, that I need to replace the door (valve) that is in the heater hose.

Any thoughts from anyone else who has done this? Should I replace the Air Mix Control Door (Blend Door)?
Is there any other possibilities? Could I oil the cable? and see if that helps?

Thank you,

ezone

Good deal, no head gasket job for you.....yet.

There are 2 separate sections to this. The doors inside the heater case, and the water valve in the heater hose. The actuator operates the blend door almost directly through the linkages you can see. The water valve is operated remotely by the cable, which is driven by the linkages you can see.

The actuator (motor, servo, whatever you want to call it) operates a few pieces of plastic linkage (you should have been able to see them), these are what operate the blend door(s). A (blend) door is an actual flat panel that moves (swings) on a pivot to redirect airflow through (or around) the heater core inside the heater housing.

You should be able to see those linkages move as you cycle the temperature up and down and the actuator arm moves.

The cable you (probably) see has one end attached to that linkage, the other end goes through the firewall and connects to the water valve in the heater hose.
You should have seen incomplete travel of the cable and lever there on that valve since the blend door wasn't making its full travel. (Now that I think about it, I guess you would have to compare to another one that worked correctly first.)



I would say to hose down the linkages you can see with spray lubricant, like silicone spray or a thin white lithium grease. Dirt in the mechanisms can take its toll. Cycle the motor several times and see if that helps.

If no joy, remove the actuator from the side of the heater case, reconnect the wires, and cycle the controls to make the actuator move throughout its operating range. Use your finger to simulate a little bit of resistance against the arm, make sure the arm (and servo mechanism) doesn't get bound up by a little load.

Then operate the linkages by hand, feel for tight spots and binding at wherever point the motor was having trouble.
Detach the cable from the valve, see if that frees up the linkages.
If no, then you decide if pulling the dash out is going to be fun.


Did this make sense?

Kevin_646

Actually, that’s very helpful. I didn’t realize the Air Mix Control Motor was controlling two things. Thank you.

So, when I pushed the pin, the motor the last quarter inch, I was actually pushing two things!

I now understand that the Air Mix Control Door is inside the heater housing.
In the hose going to the heater core, is the water valve or heater valve.

I guess the next troubleshooting step would be to separate them and see if I can tell which one moves harder.
I should remove the wire/cable from the pin on the motor.
See if the motor can move the door
See if I can push the cable, see if the water valve moves easily.

Thanks for the lubricant tip.