Heater not working properly?

acelinkacelink Member Posts: 106
edited March 2014 in Hyundai
Today, temperature was near freezing. Set the heater to 89.6F and the fan speed to max. All I got was slightly warm air (engine fully warmed up). Something is definitly wrong with the heater. Any idea what might have gone wrong here? Thanks.


  • nippononlynippononly Member Posts: 12,555

    2014 Mini Cooper (stick shift of course), 2016 Camry hybrid, 2009 Outback Sport 5-spd (keeping the stick alive)

  • jgmilbergjgmilberg Member Posts: 872
    Check your coolant level. If it's low you might have a problem with the heat, that's how it was with my friends Isuzu pickup. If the coolant level is good something else is wrong, it can be as simple as a blend door being stuck to a clogged heater core.

    Year, make, model, engine, auto/manual climate controls will make it a lot easier when trying to figure things like this out. Some of us view all topics so we don't see exactly what thread coming from.
  • acelinkacelink Member Posts: 106
    The car is a '99 Sonata with 2.0L 4 cylinder engine (just the downsized version of base 2.4L engine available in the States) with automatice climate control. It only has about 24K miles on it. A/C works fine. It was emitting slight heat on Sunday. Now, only cold air comes out.

    I checked the coolant based on jgmilberg's advice.
    It looks fine (I changed it this summer). Can anyone explain more about sticking blend door to the heat core? Can a bad thermostat cause this problem. The car now seems to warm up slightly faster than before but this could be just my imagination. Thanks in advance.
  • 0patience0patience Member Posts: 1,712
    If the coolant level is correct, then more than likely there is either a problem with the blend door actuator or a pen or pencil probably fell down the defroster vent and is holding the door from closing all the way.

    The blend door is the door that shuts the A/C core from the heater core. Door oopen, cold air.
    Door closed, warm air.
    Your vehicle has an electric blend door actuator.
    The electronic blend door actuator is located in the side of the evaporator case assembly on the driver's side. The actuator control the position of the temperature blend door based on a low current signal from the FATC module. Internally an electronic circuit accepts the signal and positions the blend door with a small DC motor. Also included is a blend door position potentiometer which provide feedback to the FATC module. The blend door actuator operates based on input information of the temperature setting lever setting signal. The in-vehicle, ambient, engine temperature sensor signal. And this A/C control module actuates the DC motor according to these signals, also controls the motor operation to adjust the air mix/blend door opening.
  • jgmilbergjgmilberg Member Posts: 872
    I would agree with opatience on this one. It sounds like a either the door is stuck/jammed, or you have a bad actuator motor that is sticking the door or the potentiometer(position sensor) is telling the system that it is in the correct position for heat. It could even be that the connector came off of the actuator motor. I don't know how hard it would be to disconnect the motor and put the door in the heat position, but if you are in a jam and don't have the cash to fix it that would work for the time being.

    A bad thermostat could cause the problem too, but if the temp gauge on the dash is saying that the engine is running at normal temp I would not think the t-stat would be causing the problem.

    If you only have 24k miles on it can you take it to the dealer and have it serviced under warranty? I know that in certain countries they have different factory warranties, that's why I ask. Is that 24,000 mile or kilometers? Here in the states everything comes with a 3 year 36,000 mile factory warranty. Even with that you are on the edge of the warranty just on the age of the vehicle, so if you can get it in ASAP before the warranty runs out, that is if it is still applicable.

    Keep us informed on what you find out.
  • acelinkacelink Member Posts: 106
    The technician replaced the faulty thermostat with the new one and this fixed the problem.

    Unfortunately, Hyundai warranty in Korea is way too short compared to what they offer in the States. Engine and transmission are covered for 3 years or 25K miles. I believe bumper-to-bumper warranty is even shorter than the powertrain warranty.

    In any case, it only cost me $32 for the replacement part, coolant and labor so I am quite happy. Thanks guys for your inputs--helped me greatly.
  • jgmilbergjgmilberg Member Posts: 872
    Well I guess we got stumped! The thermostat had to be stuck open and the gauge, if you have one, should have been reading cooler than normal. Does it now read where it used to, or higher than before.

    Oh well, the main thing is that it's fixed and you are warm while cruising around town.
  • acelinkacelink Member Posts: 106
    jdmilberg, you are right about the thermostat. It wasn't the cause of the heater problem.
    Although the heater has worked right after the replacement of the thermostat, it was back to square one the next morning. Also, the temperature guage showed that the engine was operating at the normal operating temperature all the time (before mistakenly replacing the thermostat and coolant).

    I am going to take the car back to the mechanic next wednesday. He said that he is going to replace the heat core this time. But now, after reading Opatience reply, I am a bit concerned. Will replacing the heat core cure the blend door problem? I hope he doesn't replace the parts that do not need to be replaced.
  • nato1nato1 Member Posts: 102
    If your heater core is plugged (needing replacement) then the 2 coolant lines running to the heater won't flow. So do this. Find the 2 coolant lines going to the heater core. Usually they are right next to each other with approx 3/4" hoses going to the engine. Now warm up the engine with the heater on max (no fan!). Next, feel if the hoses are warm (maybe HOT!) If they are not warm, the you most likely have a plugged core. A backflush will usually take care of this, prestone sell a kit. IF your hoses are warm, turn on the fan. One hose should go cold (or cooler than the other, actually should be about the same temp as the air from your air vents, if there is a plug). If both hoses are hot and stay hot, and you have no heat, then the problem is not with the heater core. I'd agree with the blend door.
  • 0patience0patience Member Posts: 1,712
    Wait a minute. If the heater core is plugged, one hose will be at operating temp, while the other will be cool. Not both of them cool. Both cool would indicate a blockage in the block.
  • isellhondasisellhondas Member Posts: 20,341
    Isn't it? A clogged heater core on a three year old car?

    The blend door senario seems much more likely.
  • nato1nato1 Member Posts: 102
    I would say that if a core is completely plugged (or a blockage from engine) with no flow what so ever, both hoses will be cool. If there is the slightest flow, one hose will be warmer.
    I think it's the blend door, but don't discount a plugged heater core. Engine blocks are made from a sand casting, and sometimes (yes it does happen) all the casting is not removed. It can end up in an area with small orifices (or tubes in a core) and plug it up.
    Is there a valve in-line on the hoses? I haven't looked at my '02 sonata but most car manufacturers have a vacuum actuated valve to allow coolant flow. It could be just a case of a vacuum line fell off or has failed, any chance a new stereo was put in?

    Does the air-conditioning work correctly? ie set the temp to 70 and it stays there, that would eliminate the internal cabin temp sensor as a fault.
  • acelinkacelink Member Posts: 106
    Now that you mentioned it, I had the original stero replaced with 1-din JVC CD player this summer. AC worked fine during the summer and defost worked fine when I last tried them.
  • 0patience0patience Member Posts: 1,712
    The electronic [NOT VACUUM] blend door actuator is located in the side of the evaporator case assembly on the driver's side.
    There is no vacuum actuated valve in this system.
    There is no vacuum line to come loose on this vehicle. It is electronically controlled.

    So, the options for the problem are........
    The blend door actuator connector has come loose.
    The fuse has blown.
    The blend door actuator has a problem.
    Or....... The Electronic Climate Control Module has a problem.

    But, what do I know?
  • jgmilbergjgmilberg Member Posts: 872
    Maybe the blend door actuator got disconnected when the stereo got replaced. Sometimes there is not a lot of slack in the harness and if they pulled on it until it came out farther the actuator get pulled off. Start by checking the fuses.

    The defroster setting does not really mean anything, that is another issue, that actuator only controls where the air blows from, like A/C vents, floor defroster. The blend door controls how hot/cold the air is.
  • nato1nato1 Member Posts: 102
    0patience, I am not trying to discount your opinion, just trying to cover all the bases. From my experience as a mechanic (10 yrs) and being an engineer in an automotive sensor applications division (5+ yrs), I am just pointing out things that any individual can check, along with common errors in automotive stereo installations.
    Maybe you can show this topic on the show (not an attack!, I will have to check out the show, It would be nice to be able to send questions to the hosts!!) Checking the fuse should be the first move. Can a blow-up diagram of the actuator assembly be accessed from your site? Can the connector for the door actuator be disconnected and the door moved manually to the correct position or is the gear reduction on the actuator to much to be overridden?
  • 0patience0patience Member Posts: 1,712
    Not my show. Bruce is the movie guy. Ha ha.
    Can a blow-up diagram of the actuator assembly be accessed from your site?
    Yes, if asked and the problem is explained, the guys may post it if they have time available.
    Can the connector for the door actuator be disconnected and the door moved manually to the correct position or is the gear reduction on the actuator to much to be overridden?
    No way to override the actuator by unplugging it, but..
    You can unbolt it (2 screws) and use a pair of needle nose pliers to turn the shaft to close the flap. Fairly simple to check and will help to determine if it is a mechanical problem or electrical problem. Good call.
    I apologize if I came off cross.
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