Heater blowing cold air in front but back is fine (2017 CX-9)

[megaman123]

Hey all.

This only started three days ago and has happened everyday since. Works fine in the back but up front, even after you remote start 10 minutes prior, it will blow cold air. Sometimes the right centre blows harder than the left centre. However, after about 10 minutes of actual driving, then it starts to blow hot air. That's happened all three days now.

Any idea why that would happen? So odd that it works after 10 minutes of driving despite the car already being warmed up.

Trying to avoid having to go to dealer to diagnose for lord knows how much. Just wondering if someone knows of that exact situation before I do more research this weekend.

 

[rowlands57]

If you are getting full heat in the rear within a reasonable amount of time after starting then I suspect it's the 'blend' door on the front heating/cooling system. There are small actuators that move the door(s) according to the settings on the controls. If one is stuck, or just acting up a bit, it'll cause that kind of condition.

Have you tried running the front in all the various positions including full defrost? That may help narrow things down as to whether it's the blend door or one of the position actuators.

 

[megaman123]

Good question. I should have mentioned all the settings in the front would blow cold air. Last night it was almost a problem because blowing the cold air for defrost only defrosted the windshield like 2/3 of the way. But like I said, after 10 minutes of driving, the hot air comes out and then it's not a problem.

I'll look into the actuator thing online this weekend.

 

[rowlands57]

I just cannot believe that it's a clogged front heater core on such a new vehicle so I suspect that it's something on the blend door for the heater. Given it's cold in all settings and that the air-flow redirects I think you could rule out issues with directional actuators.

If you have automatic temp settings it could be a sensor but again not sure how likely that would be. If you can gain access to see the heater blend door actuator give a look and see if it's making full motion as you go from hot to cold on the controls.

 

[Bronco Boy]

Blend door or low refrigerant.

 

[megaman123]

Wife is out with the car for a couple days so can't look at it right now but now that I've read up on the blend door actuators and realize there's one for each side, it seems odd that both sides are blowing cold air. Though yesterday, for the first 5 minutes, both vents were blowing the same temp cold air, but for the next 5 minutes the right side was less cold than the left. After 10 minutes of driving they were both blowing the same hot air.

So it sounds unlikely that both actuators would give out at the same time and both then allow heat after 10 minutes of driving. And this is four days in a row now it's doing the exact same thing. Remote started well in advance all four days too to see if it helped, which it did not. Except for the rear, which has been fine.

And whether the heat is set to auto or I change to different temps on each side, it does the same thing.

So like you guys said, perhaps plugged heater core? Or low refrigerant? I can't check the car right now but will do some research in the meantime.

 

[rowlands57]

If it is coolant temp related I'd suspect the thermostat more than the heater core, unless the coolant looks really dirty. If the coolant looks clean the core likely would not clog but not saying it isn't. To flush the core it should not be too bad if you can locate the inlet and outlet hoses under the hood.

If the thermostat is stuck open you should get better heat at idle and then is should get colder at highway speeds.

 

[Jack Rabbit]

OP really needs to be keeping this eye on the coolant temperature gauge and watching for any signs of overheating in case it's the thermo.

Bronco and Rowlands suggestions should help you pinpoint the problem.

Also, anything(including actuators) could actually go bad or get stuck at same time.

Rowlands suggestion to flush the core is great idea and simple.
If you've never flushed before, don't use too mush pressure(barely open faucet) and also use a back check valve between your hose and faucet spigot keeps any contaminants getting into your water supply( in this case antifreeze but also good to keep herbicides and pesticides out when spraying your lawn.). Run til it's clear.

I've flushed Fords but not Mazdas
so you need to check what Mazda fills with.

Make sure you have Mazda coolant on hand to final flush the water out and refill. Check to see if its a 55/45 mix like the radiator.

I don't know if it's 10 year coolant in the heater core, but if it is , makes you wonder why it would need flushed already.

Lastly , it could be the blower fan...does the amount of flow slow then it increase after 10 minutes or is it just cold versus hot?

 

[megaman123]

Thanks for all the suggestions. The flow is fine. Doesn't fluctuate unless I change it.

The coolant level was like one inch above L. Went and got the proper coolant from the dealer and filled it right to F. That didn't make a difference.

Just drove it for 12 minutes this evening and this is the first time it didn't get properly hot (it did the 10 minute thing earlier in the day). It wasn't matching the 22 celcius or 24 celcius, etc I was setting either side to. And like a couple days ago, the right side doesn't blow as cold as the left. And when it would get warm, the right side was warmer despite being set individually to the same temp or auto at the same temp. Same for defrost. The right side of it blows warmer or less cold than the left side.

Tomorrow is a manageable day to be outside. After that we get our coldest temps of the winter so far. I gotta see how frosty the windshield will be and if defrost will work.

 

[rowlands57]

If you have a 'remote thermometer' or thermal image machine you can test the inlet and outlet hoses on the heater core. They should be fairly easy to locate where they pass through the firewall, usually on the passenger side. Those hoses should heat up pretty quickly; and one should be significantly warmer than the other if the heat is running and making heat inside the vehicle. If you completely turn off the heat they should be close to the same temperature.

In the absence of any remote options you can very carefully test them by touch. Just use the back of your hand and do not 'grab' them.

They both should heat up pretty quickly assuming there is no thermostat issue. If they really never get near to hot enough then it may be a stuck open thermostat. If one is warm/hot and the other remains cold then it is likely a clogged core.

If all the above checks out and the inlet and outlet hoses are hot/warm then the issue is likely inside at the actuators/doors.

 

[megaman123]

If you have a 'remote thermometer' or thermal image machine you can test the inlet and outlet hoses on the heater core. They should be fairly easy to locate where they pass through the firewall, usually on the passenger side. Those hoses should heat up pretty quickly; and one should be significantly warmer than the other if the heat is running and making heat inside the vehicle. If you completely turn off the heat they should be close to the same temperature.

In the absence of any remote options you can very carefully test them by touch. Just use the back of your hand and do not 'grab' them.

They both should heat up pretty quickly assuming there is no thermostat issue. If they really never get near to hot enough then it may be a stuck open thermostat. If one is warm/hot and the other remains cold then it is likely a clogged core.

If all the above checks out and the inlet and outlet hoses are hot/warm then the issue is likely inside at the actuators/doors.

Thanks.

I have a digital thermometer with the long prong you use for meat or in my case soil temps. Wife drove the car for a few minutes and came back. I got 42.1 C or 108 F on the inlet hose (top) and 27.7 C or 82 F on the outlet (bottom). While she was driving the heat was on as the rear was blowing hot air, but the front was blowing cool air (in all settings).

I left it for a couple of hours and tried both hoses. They were at about 2.1 C (36 F) for inlet and 1.7 C (35 F) for outlet.

Also as I didn't confirm beforehand, I did open the rad cap when the car was cold and the cap was looking good and coolant inside was nice and green. And the temp guage looks normal. No sign of overheating.

As the blend door actuators aren't making any clicking sound like the it would with a broken gear, I'm not sure how else to check. I can see the driver's side one (haven't looked on passenger side yet). Perhaps unplug, unfasten from car then open it up to look to make sure no gears are cracked/broken and that they are turning fine? Or I guess maybe I don't have to unplug from the car but just unfasten it and take the cover off and see if the gears are moving while I change the direction settings of the heat?

It's not like it's stuck on hot OR cold. They both are blowing cold for at least 10 mintues before they blow hot air. And that's in all settings, including defrost. So the doors will move. So I'm kind of at a loss right now.

And based on the temps of the inlet/outlet hoses I mentioned above, sounds like the heater core is not clogged? And the thermostat is probably working fine? Is it possible a sensor is failing? No idea where that would be or how it works.

I'm starting to think I'm going to bring it into the shop. I do have to do the brakes on my Accord in the next few days. I'm thinking I can talk to the mechanic about that for a couple of minutes and see what he says.

 

[rowlands57]

The actuators have levers that you should be able to see moving if the blend door is working properly. At this point I think that could be your problem but a good scan tool may be needed to check it if you cannot visually see the blend door moving. It may call out the defective part.

All the other actuators sound OK based on air moving to the proper location.

PS - that blend door will be somewhere near the heater core. On the later model I'm not 100% sure where it is located and it may be inside the larger heater 'box'. If you can find a parts diagram for that unit it'll show you the place to look.

 

[youri]

There was a TSB for plugged heater core. It has diagnostic steps so you could take a look. Maybe this will help your diagnostic:

Thread 'Plugged heater core - TSB - 07-007/19'
https://mazdas247.com/forum/t/plugged-heater-core-tsb-07-007-19.123871980/

 

[megaman123]

Thanks for the TSB. It mentions checking the temps of the inlet and outlet hoses as a diagnosis for plugged heater core. Did that a few days ago and did again today. Same result. Both the same temp after letting car sit overnight (basically same as air temp outside). Remoted started car with heat set to ON and let run for 5 minutes. 29 C (84 F) for inlet and 19 C (66 F) for outlet.

Update regarding coolant level in the reservoir. A week ago I filled it right to F after I discovered it was only an inch above L. Bought the coolant from dealer by the way. The two following days after topping up I checked and it was right at F. Fast forward to today, which is one week after, and it has been driven it 6 out of 7 days (no long drives) and it's already down 2 inches from F. In the pic below you can see an F and the line. The darker colour 2 inches below is the coolant of course.

I have opened the radiator cap and coolant looks like a healthy green as it was dripping from the cap and it's right up to the top of the rad itself.

No signs of overheating by the way, since the heating issue started.

Edit: Just checked for leaks on my driveway and it's hard to tell. I usually reverse the car and park in front of those steps. So that leak spot you see, near the bottom of the pic, is probably where the coolant reservoir would be. And it kind of looks fresher than any other leaks on the driveway. However, shined a flashlight down below the reservoir and I don't see any evidence of leaking onto a tray that then leaks onto the ground.

Last night I parked it on the other side and forward, meaning the engine bay was slightly inclined as opposed to usually being on a decline but I do indeed see what could be a fresh leak. However, I also did have a 15 year old Fusion that had some leaks and that's where I used to park it until May 2021. And the previous house owner parked his work van there so there's all kinds of old leaks in that spot. I think I will drop some carboard underneath now and see if catches any fluid.

As well, I had rust proofing done on both cars early January so it dripped grease everywhere. Plus, after being below freezing for a few days, it's been above since the morning so there's snow melt going on.

 

[megaman123]

The actuators have levers that you should be able to see moving if the blend door is working properly. At this point I think that could be your problem but a good scan tool may be needed to check it if you cannot visually see the blend door moving. It may call out the defective part.

All the other actuators sound OK based on air moving to the proper location.

PS - that blend door will be somewhere near the heater core. On the later model I'm not 100% sure where it is located and it may be inside the larger heater 'box'. If you can find a parts diagram for that unit it'll show you the place to look.

Thanks for these tips.

I'm not quite sure what I'm supposed to be looking at. I can't see the actual doors can I? Without taking the dash out? The left side actuator itself is fastened to the side of the footwell. Am I supposed to see something functioning if I have someone change the heat temps/directions? For instance, saw this on a site:

"Consult the repair manual to identify which actuators control the defrost-vent-floor “mode door” and the temperature-regulating “blend door.” Then peer under the dash and locate the suspect actuator on the heater box. Have a friend switch between modes or temperatures while you watch the actuator. If the actuator doesn’t move, it’s probably bad."

It makes it sound like I can see the actuator actually doing something. I was thinking of pulling out the actuator and opening it up to make sure the gears are turning fine and that there's no cracks. Saw that on another video where one of the gears was cracked. A pain though as there are parts in the way to unscrew. Need one long screwdriver then a ratchet with pivot head to get to the other as you have little room and it's on an angle.

And the directions of the airflow are fine. It moves between dash, floor and defrost. Just that it takes quite a while before the air actually warms up. The rear heats up. It has two vents in the middle side by side. Yesterday I noticed that the right side of it was blowing warmer than the left side, though both are still warm. That is also what's happening upfront, when hot air eventually blows.


Here's a pic of a heater box pulled out of some car. I get that those three brown things are the doors that open up to direct air to dash or defrost or floor. But is there any way to view those without pulling stuff out?

Also put a pic of where the actuator is (with green wire harness) on driver's side.

 

[youri]

Thanks for the TSB. It mentions checking the temps of the inlet and outlet hoses as a diagnosis for plugged heater core. Did that a few days ago and did again today. Same result. Both the same temp after letting car sit overnight (basically same as air temp outside). Remoted started car with heat set to ON and let run for 5 minutes. 29 C (84 F) for inlet and 19 C (66 F) for outlet.

When you look at the TSB they say that the heat must be set to off when measuring the temperature of the inlet and outlet hoses to see if the heater core is plugged.

“
NOTE C: Inspect heater hose IN and OUT for temperature difference.
Using a thermal temperature gun or thermocouple, measure the heater hose IN and heater hose OUT temperature. If there is an obvious difference in temperature between both hoses, the heater core may be plugged.
NOTE: When doing this inspection, turn the HVAC blower fan OFF. If ON, the heater core radiates heat, so the temperature difference between IN and OUT hoses will generate heat even if the heater core is not plugged. »

Also, this car engine takes forever to warm up. Depending on the outside temps, i can let my car idle on remote start for 15 minutes and it still won’t blow warm air in.

 

[rowlands57]

When the actuators are operating you will see the levers and linkages move. Those parts are external and visible. Keep the fan on low and you may be able to hear them as well.

Look at this picture, it's an ebay listing for a Mazda CX9 hvac box. It may not be identical given that it could be from an earlier year but should be similar to yours. You can see two actuators in the middle and one off to the left. I'm not sure exactly which is which but perhaps the one off on it's own to the left regulates the temperature. When changing settings for direction and temperature you should be able to figure out which is which.

 

[edmaz]

....
Update regarding coolant level in the reservoir. A week ago I filled it right to F after I discovered it was only an inch above L. Bought the coolant from dealer by the way. The two following days after topping up I checked and it was right at F. Fast forward to today, which is one week after, and it has been driven it 6 out of 7 days (no long drives) and it's already down 2 inches from F. In the pic below you can see an F and the line. The darker colour 2 inches below is the coolant of course.
...

I really don't even like to mention this, but there's a well-known, systemic cracking issue with the cylinder head on a number of Skyactiv Turbo model years, including yours. And (again not happy to say) what you described above sounds a lot like the air self-purging process that these vehicles automatically do. Of course, I certainly hope that's not the issue with your vehicle, and that it actually turns out to be a much less severe and less costly repair!

 

[megaman123]

In regard to the coolant leak, I left a pizza box under the car for 36 hours (didn't drive during that time) and the dark spots are new. The lighter spots are just pizza grease. So basically the top half of the box.

Didn't overfill the coolant last weekend when we did the top up. The only dripping that occurred was when I took the rad cap off and then put back. Just a couple tiny drops. Those could have settled on a tray underneath and then when I moved the car to reverse it into my driveway and put the box under, they could have dripped down onto the box but this seems like more than that.

And it's not the rust proofing that was done first week of January. You can see this is green.

So looks like a leak is confirmed. Losing two inches from the reservoir after a week from topping up seems like a lot. Those drips in the pic are from the car sitting there for 36 hours. If I were driving it, would there be more leaking while I'm driving it, because the radiator would be in use?

 

[megaman123]

When you look at the TSB they say that the heat must be set to off when measuring the temperature of the inlet and outlet hoses to see if the heater core is plugged.

“
NOTE C: Inspect heater hose IN and OUT for temperature difference.
Using a thermal temperature gun or thermocouple, measure the heater hose IN and heater hose OUT temperature. If there is an obvious difference in temperature between both hoses, the heater core may be plugged.
NOTE: When doing this inspection, turn the HVAC blower fan OFF. If ON, the heater core radiates heat, so the temperature difference between IN and OUT hoses will generate heat even if the heater core is not plugged. »

Also, this car engine takes forever to warm up. Depending on the outside temps, i can let my car idle on remote start for 15 minutes and it still won’t blow warm air in.

Oh, I guess that means that the car should be running while the heat is set to off? Then I take the temps of the hoses? Because I took the temps while car was off and idle for a long time and then with car running and heat on. I will go now to make sure heat is off then remote start. Or should I drive it with heat off for a few minutes then check?