Very informative read about heating and cooling systems. We try to give our customers very straightforward information like this when answering their questions about automotive repair; it’s nice to see other people taking the same approach. Thanks for the great read!

Adam, the tips mentioned in the article could help. Full coolant? Feeling the inlet and outlet hoses to make sure coolant is flowing through the core and making sure there’s no air in the system.

Susan, you may have some air in the cooling system affecting the heater, this is quite common.

Sounds like an electrical short possibly in the steering column affecting the lights and cruise. Added 12/09/2010 – Since I answered this question I’ve learned of a problem that is unique to the Sebring regarding problems with the heater when the lights are on. See my answer to Cindy which also has a 2001 Sebring – towards the bottom of this page.

The exhaust sound may have been a dust shield interfering with the flywheel – exhaust leaks will not fix themselves, but if a shield was lightly rubbing on the flywheel, it could have worn away enough to not be touching anymore now. If it continues to make noise you may want to take it to an exhaust shop.

Nicole, The gear coming off for the blend door would affect the heat at ALL vehicle speeds. The reason the car is blowing warm air ONLY when your driving, could be due to the water pump pumping more water through the heater core, since the engine is turning the pump faster. Many Nissans have a problem with the radiator cap rubber seal swelling slightly preventing coolant from traveling back and forth from the coolant reservoir (plastic bottle) and the radiator. If this happens and the cooling system has a small leak (from a hose connection for instance) the system can end up with air in it, even though there is some coolant in the overflow reservoir. Particularly in Nissan vehicles if air is in the cooling system, an air-lock in the heater core can prevent the heater from working properly. See the related article (click the image below) to learn how to purge the air from the cooling system. As far as the AC, that could be a totally separate issue – checking the AC is the only way to determine what the problem is with it.

I would first check the simple things like an air lock in the system. However, it does sound like there could be a malfunctioning HVAC door or actuator. By looking at a parts breakdown of the case assembly, determine which actuator and door control the side that is not working properly *left and right are always determined when sitting in the vehicle, not standing in front of the car. After pinpointing which actuator or door assembly is at fault, the amount of labor required can be looked up in a repair manual – sometimes access is easy and other times very labor intensive (ie dash removal for access). Depending on how much trouble this is to fix, this repair could be a deal breaker.

Adam, a plugged heater core could be the problem. Checking the temp of both hoses like I mentioned in the article above is where I would start to help determine if it is or not. If it is plugged, flushing the heater core can be done with a garden hose with a sprayer attached, be sure to bleed the air out of the system as mentioned in the above article.

Domingo, you may want to check out some of our air conditioning articles, especially the one about AC gauge readings explained.

George, just filling the coolant is not good enough with most modern vehicles, since air can get trapped easily. Some cars even have bleeder screws, I remember the 2.7 engine in the Concorde, definitely has a bleeder screw in the top coolant housing – not sure about the 3.2 Liter. And as I mentioned before the Lisle coolant funnel does wonders to burp air out that can definitely cause an air lock in the heater core. You could have other problems with your Concorde, but you would be surprised how many times it’s just air in the system.

A recent article that about a Dodge Durango, which had poor rear heater performance ended up having a blown head gasket which continuously introduced air from the combustion chamber into the cooling system causing a void that never could be purged. Not saying that you have a blown head gasket, but this is something that people should consider, if air keeps bubbling up when using the coolant funnel and never seems to purge completely.

Jess, I would first check the coolant level and make sure there’s no air in the system.

After you’re sure there’s no air – you may also want to check the accuracy of the temperature gauge, by using a scan tool to access engine data and to make sure the temps are the same. I don’t see why stopping suddenly would change the temperature of your engine – so it could be a gauge issue or possibly wiring.

The fact remains the engine’s temperature varying slightly shouldn’t affect the heater performance that much, there should be heat available.

My girlfriend’s car isn’t blowing hot air when the heater is on. I was thinking it could be the thermostat because that is what was wrong in my car when i had the same problem. Is this possible.

Hi, I have a 1999 Nissan Altima. When my car heats up the temperature gauge does not go to the middle (in between hot and cold) as usual. It seems to only stay to the cold side which is making the heat in my car not very hot. I have heard about cars running hot before, but not running cold like my is doing. I have had the car for 2 1/2 years and this is the first time this has ever happened. I haven’t had any problems with the heat or air conditioning since buying the car. But also haven’t had any reason to maintain the heat or air and I didn’t know that there was anything in particular to do, to keep it maintained. Do you know what could be wrong? Thanks

hi dennisb my wifes car blows only cold air,I ran the car,thermostat seems to work fine. I felt the hoses neither are hot.the car is a 98 PLYMOUTH BREEZE.what do you suggest?thank you

dennis, I have 1998 plymouth neon and just all the sudden the car is overheating and some water dripping out of the radiator cap where the car is running hot and the heat is cold the fan will still blow but the air is cold. Is this the thermostat or what?

Hi Dennis B.
I have a pontiac Trans sport 1996. I had so many opinions regarding the heater system since it stopped working. There is no hot air coming in the car making it impossible to drive in snow. I changed the blower motor, thermostat, filled with coolant and it would not work. How could i check the heater core, how can i locate the heater core in my car and know if it is working?
The low coolant light is on in my panel, but the car is filled with coolant. maybe that might be a clue.
Please help me out.
thanks

Hi dennisb,
Great site with informative & prompt advice, great work!!!

I’m hoping you can help me out a little here: with snow and -3° here in Belfast, Northern Ireland, I need my Renault Laguna’s heater to be working, but I’ve been having problems over the past days:

The car has been blowing cold air when idle although warm when I’m driving. In order, I’ve checked the coolant level which is fine. With the car just started I then felt the inlet and outlet hoses (under the hood) going into the Heater Core/Matrix to establish if the inlet-hose got warm first then the outlet shortly after. The inlet hose did get hot in a short while, but the outlet hose took a few MINUTES later to heat up and wasn’t as warm as the inlet hose, thus indicating it could be an air-lock or blockage.

As mentioned on other sites I then drove the front of my car up onto the small metal ramps – to ensure the coolant tank/reservoir is at the highest point, then with the cap off I started the car and let it run idle for a few minutes while giving it a few gentle revs – in order to let any trapped air in the system to escape. Some gurgles/bubbles did come via the coolant tank (with cap off) although I still run it a little longer while keeping a close eye on the coolant level (ensuring their was enough inside…). However, the problem persisted.

Carefully using a screw-driver to prise open the safety-clip, I then removed the two hoses, inlet & outlet (joined together at the ends) going into the heater core/matrix, behind the dash but under the hood. This revealed the two holes leading into the heater matrix, still under the hood, (no work inside the car!).

I then pressed a garden hose-nozzle into the outlet hole in order to BACK-FLUSH the matrix, which is safe to do. Some liquid-crud and dirty coolant came out through the inlet hole as expected. I did this until the water came out clear through the other hole. I then re-connected the two hoses to the matrix-holes under the hood, ensuring the clip/s were intact again.

The problem still persisted, albeit there were times I thought it was sorted due to some luke-warm air coming through the vents for a few seconds, but then cold again.

I then replaced the thermostat with a new and original one, but still the problem persists.

I’m wondering if there’s still more trapped air in the system, or if a vent may be stuck or something, as I’ve heard the odd gurgle behind the dash sometimes when driving and, warm air comesout the vents only when I’ve been driving at least a mile or two, but goes cold again when I slow or stop.

Note: I’ve tried to clearly detail what I’ve done so far to give you a better picture, and in case the actions help someone else…

Maybe you can give me a pointer mate?

Many Thanks!
Dee

Dee, it’s possible even though you were able to back flush the heater core that it still may be restricted. For the heater core to work properly there needs to be a unrestricted flow to allow enough heat exchange. When the garden hose is hooked up and water being ran into it – the flow of water coming out of the heater core should just as much as comes out of the hose – unrestricted. Reduced flow will cause the heater not to work sufficently.

Thanks Dee. BTW 70° at the moment here in Florida Merry Christmas!

Aaaa, it’s Florida you’re based in!
I’ve been with the family the last two years – staying at my father-in-law’s villa (Blossom Hill Loop, off the 127 & 192, near the Wal-Mart and Lowes DIY.

We love Florida. I was even offered a job there with my company and was so close to taking it. It just didn’t pay well enough though and so couldn’t afford to go (while supporting my family back here in Belfast for a while).

Maybe another day.

Should be going for another 2 or 3 week vacation again though in 2010. Looking forward to it!!!

I’m envious!!

Hi Dennisb, I have a 2001 Ford F150 Supercrew. My heater will blow warm air for about 20 seconds then gets progressively cooler. I recently had the radiator system flushed and when I check, both sides of the heater hoses are hot…when I switch the heater on I can hear a faint clicking around the heater core behind the glove box. All fuses are good too. Any advice…?Freezing in Florida @ 20 degreees.

Thanks!

hey Dennis my wifes toyota 2004 camry’s heater will run you out if its moving but as soon as you stop it blows cold air fluid is good both hoses are hot ect..
any tips ?
Thanks

Hi Dennisb
I have toyota camry 1997. The heater works well while it is in parking or riding in less than 25mph. If i drive above 30mph I stop feeling any heat coming from the heater. It is also related with the temp gauge.The gauge indicates operating temperature (almost in the middle of cold and hot) while the car is in parking or idle. It drops to cold while i am driving above 50mph and then the car starts freezing. The air blowing from the heater gets cold. I have checked the coolant and it is on the right level. Can you please tell me what the problem might be?

………….coolant is to the level “full” on reservoir actually.

As far as the Toyota only heating well at slow speeds or idle, there could be a problem with the thermostat staying open. Sounds like the coolant is continually circulating and never allowed to heat up until the car stops and has less airflow across the radiator and also the pump is turning less revolutions. The t-stat should help to maintain normal operating temperature – and warm enough coolant to operate the heater.

If the heat only works while going at higher speeds I would suspect a partially restricted heater core (or low coolant).

I need some help. i have a 2005 chrysler pacifica 3.5L, AWD, last night my heater in the car stopped working. the front doesnt blow out any air at all and the back only blows out cold air. i checked the fuses, relays and it has plenty of coolant. Any suggestions??

Will removing the thermostat from my 1999 dodge caravan 3.3 auto, cause the heater not to work? When van is sitting for a little while idling and the temp. go’s up a little bit then the heater will blow warm air, but when you start driving down the road and temp. drops to normal it blows cool air.. whats up with that??

Dennis, I have a ’96 Suburban that I think has low heater air temp. The maximum it puts out is 100F on low fan speed. At higher fan speeds the output temp drops to 80F. What should I expect for a normal air temp output?

My son has a 1998 F150, We replaced the radiator because of a leak. We have no heat. Both hoses at the heater core are cold. We removed the top hose at the thermostat and the water continues to flow. Maybe the thermostat is stuck open ?

Sam, I would pressure test the the coolings ystem and do a carbon test to see if there is exhaust in the cooling system.

1. A coolant leak in the engine’s cooling system could allow coolant out and air in.

2. Exhaust in the cooling system (carbon test to determine) could mean a leaking head gasket which would cause air (exhaust) into the cooling system.

Either scenario could be the problem with repeated cases of an air-lock in the cooling system.

2002 Pontiac Montana blows hot air then cold air. Eventually it starts blowing hot again. What would cause this to happen?

I have a 2003 chevy s10, the heat is giving me some problems. I changed the thermostat and drained and replaced coolent. It takes a really long time to get any warm air out of it and then turns cold once I start driving. Any ideas would be helpful. Thanks

I have a 2001 Toyota Camry and a few months ago the air stopped blowing out of the vent on the 2 lowest settings, but would work only when the gas pedal was pushed. Eventually that stopped working. Now air only blows out when it is on the highest setting, heat or a/c. What is the problem? How much to fix it?? Thanks!

How much should I be charged to replace the heater core in my 2005 Sebring and does the dash board need to come off to do so?

I have a 96 chrysler concord it will start blowing cold air then overheat. I have replaced water pump radiator and several thermostats. Any idea why this keeps happening ?

Hi there maybe you can help. I have a 95 ford thunderbird lx and the heater blows only cold air. The ac works fine although it does start to run hot when you turn it on to high. When I bought the car the heater was disconnected and the mechanic there hooked it back up it looked like it was hooked to a t-hose or something. The low coolant light does come on once in awhile, I hope this helps you help me.

I have a 2002 Chevy Silverado-1500 series, V8. This summer both the a/c and the heater went out the same week. Never smelled anything, nor did anything drip. The coolant level is full, and both the inlet and outlet heater hoses are hot to the touch. Does that mean my heater core is bad? The fans blow fine, but it’s always cold air. I really appreciate you taking time out of your busy schedule to respond to all of us:)

I FINALLY FIXED IT! After a few months of no a/c or heater, I finally figured it out. It was simple as simple gets. A pigtail had become disconnected under the dash, probably from when my daughter sits in the middle with her feet dangling nearby, or from my wife and the vacuum hose. Regardless, your step by step diagnosis above really helped in telling me what “wasn’t” the problem. Very thorough self-diagnosis. Again, thanks!

If the car does have a blockage like described in your very helpful article – is the car safe to drive? My mechanic friend is coming to look at the car in 3 days and I wonder if I could do more damage if I am still driving it? My journey to work is 4 miles each way so a very short journey?

Thanks

Thanks for this great article, I am wondering if you would know what would cause warm air coming out of the front air ducts but cool air out of the defroster, this is when I have the heat on.

Thanks for your comments, I too find it strange as the heater doesn’t blow out hot, but warm enough for the bottom and center when selected, the only time the temp gets cool (while in heat mode) is when I put it on defrost.

I would check the things mentioned in the article. If you are asking about changing the heater core, no it’s not an easy one – the Dodge Intrepid requires dash removal to access the heater core for replacement.

Leeanna, first off I would check the accuracy of the gauge. It shouldn’t take that long for the engine to reach operating temperature (even if the thermostat was stuck open). A scan tool can be used to check the data screen to see if the temp reading coincides with the gauge in the dash.
Second, if a repair shop has replaced the heater core twice in the last year I would suspect a very dirty cooling system causing the core to get restricted quickly (clogged up). Have the repair shop explain what has caused the heater core to need replacing after such a short time. Some systems may require a new radiator and a thorough flushing to clean the system out enough to prevent the heater core from getting plugged up again quickly. This is particularly common when someone has added stop leak in the cooling system. The warm air for 3-4 seconds also leads me to think there’s restricted flow due to contamination like rust or stop leak. Good Luck.

My 2001 Chrysler Sebring temp gauge keeps flucuating and some times hits HOT and the heat isn’t blowing hot. I had it flushed and a new thermostat put in… I don’t know what to do now!!!

Get help from a dealer tech if you are able to do some work yourself and save some money $$. Ask your question below to get an answer quickly.

I have a 03 Neon and the heater has been blowing cool air. Last year the heat worked great. So far the thermostat has been replaced and the blend door has been checked. Both are fine. The coolant level is fine also, though it is a little dirty. What else should we check? Thanks.

Dee, if the coolant level is low at some point or like in your situation, the coolant was changed – air pockets can be trapped in the system. This seems especially true when it comes to Nissans. Using the Lisle coolant funnel to fill the system is one method to help burp the air out of the heater system. See the related article for more information on this (click the image below).

If there’s still a problem after the air is bled out of the cooling system, then there could be a door or actuator problem, but first eliminate the air lock problem.

Regarding the air entering even with controls turned off – The system is NOT completely air tight (it is normal). This seems to be noticed more when it is COLD outside.

Bryan, sounds like air in the system. I would use the Lisle coolant funnel as mentioned before. Some of the 3.4 Chevys also have bleed valves to help get the air out. If air locked in the system isn’t the problem I would suspect the thermostat. Good Luck

Bryan, you can read more about the funnel below – also the link going directly to the product for sale too.

Related Article and Specialty Tool
Lisle Coolant Funnel for sale

How to Use the funnel with YouTube Video

B.T. You may want to ask a Toyota dealer tech. A Toyota tech will have access to repair information and has personal experience with your model car. Get started by asking in the box below. Good Luck.

Chelsea, On cars that use vacuum to control the doors in the dash – I would say the most likely cause of the mode defaulting to the defrost vents is a vacuum leak.

The Chrysler Pacifica does NOT use vacuum to control the HVAC (Heating and Ventilation & Air Conditioning). It uses low voltage electric actuators to change the modes, overseen by the A/C Heat control head.

Here’s something that may help with Pacificas when the mode is stuck in any one position like you have described:

Pacifica HVAC Reset Procedure – Calibrate Steps
Try running the calibration test. Hold the POWER button and the RECIRCULATE button down at the same time for about 5 seconds. The control head will start flashing to indicate the test has been activated. The self test should be done in about 20 seconds. If the control head continues to flash, this means there’s a fault code stored in the Automatic Temperature Control (ATC) system. An automotive scan tool will be needed to access codes from the ATC system. Good Luck.

chunky-jeff, first – it’s not normal for stop leak to be used, especially to stop a leak from a new head gasket. Stop leak could restrict the flow of coolant in the heater core, radiator and ports in the head.

What I would be asking myself if I was working on this car is “what caused the head gasket to fail originally?” Or was it even bad to begin with since the overheat problem is still present.

It sounds like it could be a faulty impeller on the water pump. To check for water pump flow have the mechanic do the following.

Measure three temperature readings from the car with an infrared thermometer.

1. Radiator temperature.

2. Engine block.

3. The vent temp with the heater on maximum.

The three temperature readings could indicate that the water is not flowing properly. A cold vent temp with a “warm” engine and a cool reading at the radiator is the main indicator.

A more direct way to check flow from the water pump is to remove the upper radiator hose from the radiator. Have someone start the engine for a few seconds to see if there is water pumping out.

The impeller on the water pump could come loose or can deteriorate from rust or electrolysis due to lack of maintenance or proper ground straps.

Tony, sounds like a bad connection or faulty blower motor for the front not any blowing air. This will require using a tester like a multi meter or power probe to help pinpoint the loss of power. Sometimes you can tap on the blower motor and make it work temporarily. If this is the case the blower motor will likely need to be replaced. Not much of a surprise especially since the car has been in a flood.

As far as the rear heater, it will take some diagnostic steps to determine the problem. Either consult a repair manual like can be accessed from our auto repair manual page, ask a dealer tech on the car questions page or visit a local repair shop. Good Luck.

“Funny smell” is the uncle that sent his pregnant niece on her way with a leaking cooling system! Just Kidding.

Jillian, could be a hose, freeze plug, water pump etc. Have it pressure checked and repaired. After the system has been repaired and there are no coolant leaks the heater should work again. Like explained in the car repair article above, the heater uses coolant to heat the heater core, so if there’s no coolant or the system is low it cannot work as designed.

I have a 93 Buick Park Avenue. The temperature gauge in warmer or hotter weather runs at normal while on the freeway but then will heat up to 210 when stopped at a light. Now with the cold weather in the morning, 20 to 40 degrees) the temperature gauge heats up about 180 on the gauge (20 degree increments on the reading.) Then after the stat opens in goes down to 140 while driving on highway. Then when stopped for a few minutes will go up to 180. The heater is blowing hot air when warmed up and the car is running good. I can’t figure out why this gauge is bouncing around from 195 when warm outside to 210 when stopped and running at 140 now that it is cold? I cahnged the stat last summer and the coolant. Coolant level is fine. I wonder if the temperature gauge is just bad?

my 1997 ford f150 heater doesn’t blow hot air, for a month all it did was blow hot no matter what setting you turn it it still blows hot , now its the other way around all it blows now is cold. the back of the knob is not cracked either.

I have a 01 Dodge Caravan, it has a lot of cold air coming out from the passenger side floor, everywhere else it blows hot air. The cold air is not coming out of the actual vent but from an rectanglar opening next to the blower motor.

Thanks!

Rob

I own a 97 Pontiac Bonneville, my hoses get hot but it blows cold air into the car. I had my thermostat replaced plus the coolant and all that is full. what do you think the problem could be I was told the doors might be froze shut.

Have a heating problem with my 1998 Renault Laguna. My local garage claims that it has changed the heater-matrix, water pump and thermostat, costing me £350 parts and labour so far this winter (2010). The engine-radiator never over-heats. There is no water leak. There is no oil leak.

The car has heat up at idle speed as the car temperature meter goes up from cold to normal mid-way. The heat fades away gradually when the car is being driven over 30mph cruising speed as the temperature meter goes from normal mid-way down to cold level. There is heat at motorway speed.

Without seeing the car, another garage now claims that the car may need a new pollen filter to cure the heat problem. Is that right? If not, what else would cause the problem?

Dennis, I bought a 96 Chrysler Sebring with 160K miles from a friend seven months ago for $2K but found out last month that the heater isn’t working, neither is the A/C. I took it in to Sears and they gave me a quote of $900 because of the time it would take to get to the heater core-they almost didn’t want to touch it because of access would mean going through airbags area(liability). I told them it’s not worth it and figure I’ll survive the winter using the heat from the engine since I get a small amount every few minutes. My question is, is this going to be enough for the windshield defogger this winter?

Thanks Dennis, I would never have known the AC works in conjunction with the heater to defog the windshield. I’ll look into having it flushed. At least now I have some hope of keeping warm this winter.

Mari, sounds like it’s most likely the control head on the Toyota Highlander. I’ve heard of the connections being loose for the metal ribbon between the circuit boards. It may just be a matter of removing the head and inspecting for loose connections and securing – or the head may need to be replaced. Good Luck

Nathan, it’s normal for the heater to take several minutes to heat up. As far as the temperature differences for the AC and heat respectively this could be normal too. Sometimes drastic differences from side to side is from systems that are not full.

You may also be interested in reading our article on the following link regarding airflow you mentioned –

Low Air Flow in Dodge Rams

Trish, no it does not. See the next page for more information on troubleshooting this particular problem. When the heat works just a little or only when more gas is given there are a couple of things to check.

Next Page

Cindy, this is an unusual problem but not unheard of! More than likely it’s the control head. Some techs report that one way to test is to temporaily make an open orange wire that goes to the control head (by cutting it). See if the problem goes away after doing that – it’s the easiest test (without going into details). If the problem goes away, then the control head needs to be replaced and the orange wire repaired.