Hello. I searched this forum and haven't come up with anything and I'm hoping someone may be able to help me. On my girlfriend's 2001 Eclipse GT the heat will blow warm and then just go cold. I found that by putting the automatic transmission into manual mode and letting the rpms rise up the air blows hot but at low rpms the air blows cold. Does anyone have any idea why? I'd appreciate any help that you can provide.

Thank you.

 

get the heater core checked

 

What is the temp reading? Check the radiator usually when the heat is cold it's cuz there is no liquid in the lines to transfer enough heat to be effective. Check your floorboards for antifreeze indicating a line/the heater core being cracked and leaking.

 

Thanks for the quick replies! The car will heat normally... when it's half way up which is what it will always go to it should be fully heated I would think. The thing is it will have heat and then it will just die 2 seconds later and then 10 seconds later it may return to heat. If it were the radiator I don't think it would be so instant with the heat on heat off effect and it wouldn't heat at all. I guess it could be the heater core but could it be something simpler (and probably cheaper) like a door or a malfunctioning switch? It's odd how it will be hot air one moment and then the next it's cold air. Also, please keep in mind that when it's blowing the cold air if I up the rpm's to say 3000 it will blow hot air almost immediately. Again, thank you for any help you can provide me.

 

sounds like you are low on radiator fluid or there is a clog in the lines because the heater core runs off the heat of the motor that runs through a small radiator "heater core" and your fan blowes air over it and than that now hot air comes through the vents the core is not getting sufficant water flow or teh fluid is low.

 

Yep I agree sounds like you're low on antifreeze. Sounds like what's happening is when the engine cools off or is cooler the thermostat is closed so there is more fluid to circulate through the heater core then when the engine warms more the thermostat opens allowing the coolant to go into the block thus leaving the heater core without coolant to transfer heat. Check fluid levels and let us know if that's the problem or not.

 

Crawl up under the drivers side lower dash and take a look at the blend door cable as someone manually switches from cold to hot on the HVAC controls. (you see the cable moving as someone moves the temp **** back and forth) Chances are, the blend door is NOT switching back and forth. The blend door is driven by a cable that can bend as it's moved back and forth. It can bend either because the cable holder has released the cable- or the cable is kinked. It may move the blend doors somewhat, but not at full throw to hot. This can explain why you have very little heat coming form the heater core as the blend door does not open all the way towards hot. Good Luck!

Joel, CA

 

dang i totaly spaced that!

 

What do you mean you totally spaced that? I hadn't thought about the temp selector cable as a part of the problem... Yeah that's something else to check... LOL

 

Thanks for all of the advice. I'll check for all of these things. I am not sure about the blend door cable though. The reason I say that is because the heat will be set to hot and the car will get to normal operating temperature and the heat may be great for half a mile or 50 miles... but driving along doing nothing different at all it may just turn to cold air out of the blue and then a little later it may go to hot air again. Could the cable move on its own or is the low antifreeze a more reason that this is happen? Again, thanks for all of your help!