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Hi everyone,
I have a 1996 honda civic and we just bought it. Went to use the heater for the first time a few weeks ago and got absolutely no heat at all. The engine gets warm but no heat in cabin. We checked the thermostat and replaced it just in case that may have something to do with it. but no change. Then we checked the cable slide to the heat control valve. It was stuck - we thought we found the problem but after disconnecting the cable and moving the heat control valve manually we could only get a bit of heat (29C or about 88F). So we thought maybe we have a heater core that needs to be flushed. We checked the hoses going into and out of the heater core and they both felt hot so we skeptically did the heater core flush. The flush did not result in much dirty coolant coming out, just nice clean coolant. I also let CLR sit in the heater core for one hour and when all was done we only got a marginal improvement (33C or 94F). The air flow baffles/valves in the cabin work as indicated on the buttons when we push them. I am stuck - why are we not getting heat in the cabin if both the hoses going into the heater core are hot to the touch? It's a good car yet so I'm hoping we can get this fixed before winter sets in or it will have to be sold or parked for the winter.

 
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deleted your duplicate thread, please refrain from creating duplicate threads.
could try swapping in a new heater core, could be that the coolant isn't flowing through the entire heater core, only part of it

 
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Thanks for the input. "Swapping" out a heater core is a big job, is there any way to tell for sure this is the issue before I attempt that or could there be something else that might account for the issue I'm experiencing?

 
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See if the water valve is not fully open? (even though the lever position might appear to be correct, the valve can fail internally)

 
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The valve would be my guess as well. Can you see a way to temporarily bypass it?

My only other thought is maybe there's a blanket of dust over the heater core (or A/C core) on the outside where the air passes through (inside the HVAC box under the dash) I would remove the plastic at the base of the windshield where the air inlet is and look. Remove the cabin filter if the car has one, set the heat to hot, floor, and then use an air compressor to blow air up the vent by your feet backwards through the system. I've never seen a heater core with enough dust to affect it, but the AC core in there gets condensation and dust sticks to it. I've seen those plugged up solid like a lint trap in a clothes dryer that has never been cleaned. -Maybe the liquid is fine and airflow is the issue

 
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Thanks for the suggestions. I can bypass the heater valve easily so we will see what happens after that. I will also take a look at blowing any dirt off the heater core or the AC core - briefly looked at it the other day hoping the heater core was easily accessible - but it wasn't LOL. There is a cabin filter as well.

 
Rep Power: 517

You sure? Last I checked Civics didn't get cabin filters until 2001

 
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my guess is the bypass door is not opening, the door that sings open has a plastic piece that breaks, thats what happened to me. i believe i posted pics and the story on here