Hi Everyone, I've got a 99 Honda Accord and I've been fighting heater issues for about 2 years now. There really doesn't seem to be any rhyme or reason as to why it is not working properly and the shops have not been able to really figure it out either. The core is not leaking and the hoses in and out of the heater core are good and hot, so the water is circulating. Last time I had it worked on was exactly 1 yr ago. The shop flushed the heater core and actually reverse flushed it, but I'm not 100% sold that that is actually the issue, because nothing ever really flushes out. The heater has been working great up until 2 days ago when my alternator went. I've replaced the alternator and now the only time the heater seems to blow warm is when I idle it up to about 3K. As soon as I back off, the heater cools off. Could this be the core is just bad or could it be something with electronic doors not opening and closing properly due to the issue I had w/ the alternator. The car has climate control, and I just hate to pull the heater core unless absolutely necessary because it is such a huge job and will cost lots of $'s. Any help would be very much appreciated. Thanks in advance!! Minnesota is freaking cold w/o heat!!!

 

I found out something interesting on my 95 Accord (no climate control) which is the blend door controls the heat and cooling. I have the water valve open(heat position) and cable disconnected and the air is the coldest it has been since new and the heat works just fine. I am not familiar with Honda’s climate control but if it uses vacuum it would explain why you only have heat up to a certain RPM.

 

So if it does run off of vacuum, would it need a new climate control system do you think??

 

If it runs off of vacuum you have a leak. There is usually a bottle in a climate control system to store vacuum also.

 

Hey Kris,
Thanks for the info. Now the next thing. I've had this issue reaccuring for like I said....2 yrs and no one has ever done anywork w/ the vacuum system. So what I'm getting at, is if it had a leak, I'm thinking it would leak all of the time and I would never have a strong heat or air system, which is not the case. I've had a strong heater...even when it was 20 below zero and the issue just all of a sudden came back this week when my alternator went out. I guess this could be coincedence, but seems so odd. That is why I keep thinking that may be there something electrical messed up. This is so frustrating!!!

Well, I will keep you posted and if anyone else has any idea, I would love to hear them!!

Kind Regards,
Nate

 

I wish I knew you system but I don't. I will see what I can find out.

 

does the engine reach operating temperature? if not, check/replace the thermostat. otherwise it sounds like either your core is restricted again or your blend door is not working... being that you have climate control, your blend door is MOST likely going to be electronic... have you tried checking fuses? may be as simple as that.

 

1998+ accord has electric motors to drive the air-blend doors. Another electric motor drives the water valve (with a cable through the firewall).

Better yet, the EX V-6 might have automatic climate control, which has even more fancy control. THAT one I'm not real familiar with, but the actual heater unit with motors is likely the same.

 

So I may be on to something that leads me back to a bad heater core, but not sure. Every so often, I get this greasy film on the inside of the front windshield and I found a guy who said that is a sign that heater core has a leak and the air blowing around the heater core is catching that coolant and blowing it up on the windshield. The crazy part is that I don't smell anything and I don't have any dripping into the passenger compartment area, so if there is a leak, it is extremely small.

I checked the coolant valve and that seems to be opening and closing properly. I also checked the coolant and that seemed to be low, so I added some last night but didn't change anything much. I don't think it is a blend door issue either because if I crank the heat all the way up and idle the car up to 2K, she blows super hot.

I think what I'm gonna do is take it in and have the core cleaned out again and hopefully get through the winter with it. Thank goodness we have had some nice days here in MN lately so I don't freeze!!

Thanks to everyone for their comments and keep them coming if you think of anything else I can do or have a magic cheap answer for changing out the core.....HAHAHAHA!!!

 

If the heater core is leaking it will smell pretty bad. I would suggest seeing if your cooling system holds pressure by using a cooling system pressure checker and see if the needle falls. The coolant went someway.

I had a weird one before on an Accord that everything checked out but no heat no matter what was done. We decided to replace the heater core and when we got access found something had made a nest around the core. I guess it liked the heat.