Heater/Defrost blowing cool air at idle
 

Does anyone have any suggestions for what to do when your heater and defrost is insuffiently heating the cabin area of the car at idle? I am working on a '97 Accord EX. Last week when the temperatures hit new lows it would not defrost the windows after idling for 10-15 minutes. However it works fine at higher rpms. I confirmed with a thermometer that while idling(outside air was in the 60s) that it would blow about 105Fbut would increase to about 140F at 1500 rpms. The air coming out of the vents is mildy warmbut not hot. Last summer I had to replace the a/c fan motor, thermostat, and upper/lower radiator hoses. Iopted for an aftermarket thermostat and I am thinking this may be my problem.

After inspection I found that the valve allowing coolant to flow to the heater core appears to be opening from visual inspection and I can feel warm coolant flowing through input and return hoses. The temperature drops on the return hose when heater blower is on. I listened for vaccum leaks and couldn't find any for the control switches. Coolants flows through upper and lower radiator hoses once vehiclehas warmed up.

I am not sure what I should do next and I am consideringswapping the thermostat again with one from the dealer. Has anyone elseencountered problems with aftermarket thermostats? Where should the gauge be at normal operating temperature on these cars? I thinkthe enginemay not be reaching it's optimal temperature and the cluster temp gauge onlyreaches about the 5/8s mark without increasing engine speed. Again, if you increasethe engine speed just a little everything seems to work fine. I'm not sure thoughif this is because morecoolant is flowing through the heater core or if the engine just needs to be warmer.

Any feedback or thoughts are greatly appreciated.

RE: Heater/Defrost blowing cool air at idle
 

try a Honda t-stat,, also make sure that the heater valve is adjusted properly ..........
In other words when you turn the knob all the way to hot, look under the hood at the heater valve make sure it is fully open,, it might need to be adjusted ,, also look under the dash rt side,,left of glove box on center console ,, there is a little plastic cover you need to pop off,, there is another cable that comes from the heater panel, make sure it is hooked up and adjusted properly

let us know

Oh Welcome to the forum ;)

RE: Heater/Defrost blowing cool air at idle
 

Thank you for your recommendation. I got around to replacing the thermostat with a dealer's this morning. Filled & bled the cooling system and things appears to be working correctly now. I won't know for certain until another cold morning but I am now getting air at 140 degrees F at idle which is a big improvement. Although I'm not sure the thermostat was the problem in this case. When I took off the radiator cap it was in pieces and I had to fish out part of it from the radiator. Since I had already purchased the thermostat I went ahead with the replacement. Do you think the thermostat was the culprit here or would a faulty cap cause similar problems?

RE: Heater/Defrost blowing cool air at idle
 

Your problem really sounds like thermostat, not cap. But OTOH, maybe a peice of broken cap got to the thermostat.

If the cap was in peices, then maybe there's a few more peices still swimming around in there. Someday they're gonna get stuck in the thermostat. Or in the waterpump...

RE: Heater/Defrost blowing cool air at idle
 

I'd replace that cap as well just to be safe (it's a cheap part) if you haven't already, my guess would be that you did have a thermostat problem but like jimblake said it may have been caused by a faulty cap.... replace the cap and give it a test.... I was laughing pretty good when you said 60 is cold.... It's amazing how much different weather feels when you're used to higher temps.... 60 is shorts and a t-shirt to me *L* we just got over single digit cold and now it's a warm spell!!! 20 today!

RE: Heater/Defrost blowing cool air at idle
 

Safe bet thathe already did since it came off in peices...

RE: Heater/Defrost blowing cool air at idle
 

If the cap was broken, that means the system was probably not pressurizing properly which could also affect the heating system.

RE: Heater/Defrost blowing cool air at idle
 

Thanks sir_nasty for your thoughts. I replaced them both when I did the job and I haven't had any problems since. I did test the old thermostat by placing it in a pan on the stovetop andmonitoring to see at what temperature it begins to open. Result was that it started to open around 175-180 degrees and was fully open at 194. Additionally it would instantly close when removed and placed into cool water. Leads me to think the radiator cap was the problem in my situation.