Where Did My Heat Go???

[GrolarBear]

The other day I was driving my 2012 SHO, it was warmed up and heat coming out the vents and suddenly it just started blowing cold air, just like if someone just flipped the setting and turned the AC on (it literally changed in something like 10-20 seconds). It was in the teens outside, it's been cold. Both sides are the same temp, once the engine warms up it's not as cold as outside, but I'm guessing its like 30-40*. Settings don't matter (auto/manual, any set of vents, same or different temps on each side...)

I did some googling and didn't really see anything that matched exactly, a lot of "passenger side cold" and "goes cold at idle or light cruise" (seems to be low coolant). I checked the coolant (it's fine, looks good, tests good). The passenger side cold stuff seems to be the actuator but a lot of people report that disconnecting the battery seems to fix it.

Well it doesn't match but it won't hurt to try. I disconnect the battery, let it sit for 15min and reconnect. I take it for a test drive and everything appears to be working once the engine heats up. I drove it to the gym, to a friend's house, it works fine. I leave to go home. No heat again.

Any clue what is going on?

 

[JimC]

I've had random heat issues on my 2016. Suddenly the heat kicks on high and blows like mad, turned system off then back on and it reset. Next morning, no heat, no blower. Took it in and no problems at the dealership of course (although they found a problem with the heated driver seat and replaced some parts).

Then last week we were traveling and suddenly the heat went full blast again. Shut it off and when I turned it back on both sides were set to "high" for temperature.

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[limited02]

Look into the blend door actuator issue that's known to fail on our cars.

 

[xFallenxCripplex]

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[GrolarBear]

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Um if I didn't already mention that I checked the coolant level and that if I disconnect the battery it works for a while. If I'm literally driving along and have full heat and it just turns off it can't be a blocked radiator and if the coolant level is highenough it's not like it's sloshing back and forth.

 

[GrolarBear]

Look into the blend door actuator issue that's known to fail on our cars.

OK, I'm under the impression that there is a driver's and a passenger side blend door actuator. If both sides are doing the same thing wouldn't that mean the actuators are fine and responding? I've seen the big list of bend door actuator posts, but they all seem to only affect the passenger side.

 

[GrolarBear]

FWIW, I tried disconnecting the battery again last night and as of right now I have heat and it's still working after driving it 2x. I suspect that a few more times and it will stop again, but we'll see

 

[Mitral]

Do you still have the issue? My car has similar symptoms. Regardless of the temperature that I set the car blows the same amount of Luke warm heat. It is the same on both sides. I removed the positive terminal and that didn't resolve the issue. I also verified that the coolant level is ok.

 

[GrolarBear]

Do you still have the issue? My car has similar symptoms. Regardless of the temperature that I set the car blows the same amount of Luke warm heat. It is the same on both sides. I removed the positive terminal and that didn't resolve the issue. I also verified that the coolant level is ok.

Honestly I don't know. I drove it 2x since I disconnected the battery (FWIW, if you're disconnecting the battery on most cars you're better off pulling the negative for safety reasons), but then the weather has been decent and I've been driving the truck (family truckster, the only thing I can fit the twins in car seats and the dog in at the same time) and the "race car" and the SHO has been sitting parked for about a week.

 

[Mitral]

Thanks. I will unplug the negative and see if that changes anything. Regardless of what temperature I have the heat at the car blows the same temperature but different fan speeds

 

[6500rpm]

Two things, I have training from multiple car manufacturers due to the fleet mix and the whole battery disconnect is termed a hard reset. Our training is to disconnect the positive cable from the battery and hold it to ground. By doing this it takes any stored voltage in the modules to 0 volts and in essence puts them to sleep in the cas e of a logic lock condition. I have what amounts to a 2' jumper cable that I made to do this. It typically takes less than 30 seconds to put the modules to sleep this way, longer if it makes you feel better.

You can tell if your kid has a fever by using these magic things we call hands, they can detect a very small temp change. Use them. If your heater is working properly, reach back and feel the inlet and outlet hose to the heater core. They should both be nice and warm with only a slight difference between the two. Now if you suddenly loose heat, feel them again. If they aren't still warm, its a flow problem to the core. If the inlet hose is hot and the outlet is cool, it's a flow problem like a clogged heater core, and if they're both warm and no heat..you have to start looking at things like blend door actuators and blend door hard parts. Sometimes in the case of a mechanical breakage in the blend door, you can actually hear the door slam shut as it flops from the hot to the cold position in the HVAC box.

Just a few things that may help you isolate the problem, you can easily use a decent quality temp gun on the hoses if you can't or don't want to physically touch them with your hands. Just remember 98.6 deg is normal for your kid, if they have a 101 degree temperature your hands have the ability to detect it. You can also apply the same idea when it comes to high and low pressure A/C lines when summer comes.

 

[Mitral]

Thanks 6500RPM. I have a temperature gun and the inlet pipe temperature to the heater core has been consistent around 105 degrees and outlet is around 100 degrees. Should I still flush out my heater core or should I start looking at the blend door?

 

[markathome]

Make sure the coolant level is at the top of the full line in the reservoir.
If so, check the blend doors, but if those, normally you would hear clicking noises.

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[Mitral]

Mark the coolant is to the top. I am going to check the blend door!

 

[6500rpm]

If it was 105 on the hoses and blowing cold at the vents I'd think be looking at the blend door. The only other thing I can think to look at is to set your display to show engine temperature and note if its running near center when you don't have heat. If the thermostat was stuck open and it was cold enough outside it's possible to over cool the engine and you'd see the temp gauge drop like a rock. From what you posted, I doubt that's your issue, but worth mentioning.

 

[Mitral]

Any tips on the blend door? How do I get to it? I opened the glove box and checked the motor and it seems to be working ok. I removed it and made sure the gears were not broken

 

[6500rpm]

Without actually looking at it I can't be sure, but I'd thing with the screws out of the blend door motor and the harness detached you should be able to chand the mode from hot to cold by rotating the motor body by hand. (the gears should be locked stationary and with the mounting screws out I'd think you should be able to rotate the whole motor thus manually moving the blend door from hot stop to cold stop). I'd get it up to operating temp and rotate it and you should feel a positive stop in both directions as the door bottoms out and get full heat and full cold but don't get over zealous cranking on it, it should move freely. Is it just blowing cold all the time now or does it intermittently fail?

 

[GrolarBear]

FWIW, Mine hasn't done it since I last mentioned about disconnecting the battery... for now it appears to be working...

 

[Mitral]

Thanks. I am going to remove the negative to see if that changes anything. I get the same heat from both sides regardless of temperature. For kicks I put the car in neutral and revved it keeping the temperature at 90 with a full blast of air and the air got hotter. Maybe a plugged heater core? Maybe a weak water pump? The coolant level has been fine for the past 800 miles.