# Aux Heater Question



## Cruzator (Dec 31, 2014)

I was wondering if there are certain parameters that inhibit the aux heater operation (coolant temp. or ambient temp.). I was messing around with mine the other day, and it didn't appear to increase the temperature (based on a thermometer in the duct). But it was 47 degrees out and the coolant temp was past 170F. It's always worked fine when cold (both ambient and coolant temp). I was wondering if it is left on, will it shut off after the car warms up, or does it always stay on. I know some people have said it does cause a slight drop in mileage, so I am assuming it comes on whenever turned to full hot and it stays on. Just wondering . . .


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## BradHerr (Sep 29, 2013)

I've noticed mine quit working as well. I was hoping it had something to do with ambient temp being over 32°F. I haven't looked into it yet to see what conditions have to be present for it to come on. I know it only comes on when the heat is set to the maximum hot position. 


-Brad


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## diesel (Jun 8, 2013)

It seems like it only stays on until the temp gauge starts moving. I say this because when I start driving, there is a distinct drop in heater output on a cold day once the temp needle starts moving. I attribute this to the aux heater shutting off once the coolant reaches a predetermined temp.


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## BradHerr (Sep 29, 2013)

BradHerr said:


> I've noticed mine quit working as well. I was hoping it had something to do with ambient temp being over 32°F. I haven't looked into it yet to see what conditions have to be present for it to come on. I know it only comes on when the heat is set to the maximum hot position.
> 
> 
> -Brad


This morning the ambient air was 19°F and the auxiliary heater worked as designed. 
I have not noticed the auxiliary heater shut-off when coolant temps come up. I don't think I have paid that much attention to it. It does make sense that the electric heat would be unavailable when coolant temps start to rise. 


-Brad


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## MP81 (Jul 20, 2015)

It'll definitely cause a small mileage hit, because the extra current draw puts more electrical load on the alternator, which in turn puts more physical load against the engine via the pulley. Would make sense that it turns off once the engine itself is capable of supplying enough heat, though.


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## Cruzator (Dec 31, 2014)

Thanks for the info!!!


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## CruzeDan (May 17, 2015)

On today's episode of ripped from GM SI: HVAC description and operation-

Auxiliary Electric Heater (Diesel ONLY)
Models equipped with a diesel engine are also equipped with an auxiliary electric heater grid to provide faster cabin warm-ups in cold climates. The auxiliary heater grid is mounted in the low-center of the HVAC module, where heat is transferred from the grid to air which is directed to the floor outlet ducts. 
The auxiliary heater is enabled when:


Cabin temperature is set to MAX. Even 1 detent off of MAX. cabin temperature will disable the electric heater.
Turns on with coolant below *80°C (176°F)*. Once above, if falls below *75°C (167°F)*, it turns back on.
Turns on with OAT below *12°C (54°F)*. Once above, if falls below *8°C (46°F)* can turn back on.
The amount of heat that the electric heater supplies will vary based on the internal heating regulator that controls to a thermal limit (for example it will reduce power at lower blower), the battery state of charge, and the generator duty cycle.


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## diesel (Jun 8, 2013)

CruzeDan said:


> On today's episode of ripped from GM SI: HVAC description and operation-
> 
> Auxiliary Electric Heater (Diesel ONLY)
> Models equipped with a diesel engine are also equipped with an auxiliary electric heater grid to provide faster cabin warm-ups in cold climates. The auxiliary heater grid is mounted in the low-center of the HVAC module, where heat is transferred from the grid to air which is directed to the floor outlet ducts.
> ...


Great info! Thanks for posting!


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## Cruzator (Dec 31, 2014)

Thanks, CruzeDan! That's exactly what I was looking for!


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## Kexlox (Nov 4, 2014)

CruzeDan said:


> On today's episode of ripped from GM SI: HVAC description and operation-
> 
> Auxiliary Electric Heater (Diesel ONLY)
> Models equipped with a diesel engine are also equipped with an auxiliary electric heater grid to provide faster cabin warm-ups in cold climates. The auxiliary heater grid is mounted in the low-center of the HVAC module, where heat is transferred from the grid to air which is directed to the floor outlet ducts.
> ...


I guess this explains why it never seems to get warm for me in the mornings. I leave it on windshield defrost, thinking the aux heater would help with the morning frost/ice on my windshield. Since it only heats the floor air, I will have to start leaving it on floor/windshield.


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## Cruzator (Dec 31, 2014)

Mine works on defrost, and very well, I might add.


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## VtTD (Nov 5, 2013)

Kexlox said:


> I guess this explains why it never seems to get warm for me in the mornings. I leave it on windshield defrost, thinking the aux heater would help with the morning frost/ice on my windshield. Since it only heats the floor air, I will have to start leaving it on floor/windshield.


I'm not too sure about that. Mine definitely blows warm air out of the upper vents from the aux heater. That said, it's pretty weak compared to the engine heat, although does make things more comfortable when the car is cold. I notice it heats things up better when the blower speed somewhere around the middle. Too high and I think the cold air just overpowers it... for the most part.


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## Cruzator (Dec 31, 2014)

I agree. I usually run it on 2 or 3 (blower setting) and it definitely gets warm (not hot). It works no matter what mode is used (i.e. defrost, vent, bi level, heater). I monitor the duct temp. vs the coolant temp.,and it's always warmer when aux. heat is on, until the coolant get very warm.


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## roadhawg (Apr 24, 2017)

> The auxiliary heater grid is mounted in the low-center of the HVAC module


 Does anyone know how to troubleshoot this heater ? Is it accessible through the glove box ? 
Not getting much heat under 40 mph, but getting a good amount of heat at 60 mph +. 

I don't think I'm getting any "Reinforced Electric Heating".

Any ideas ?


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## CruzeDan (May 17, 2015)

If you have an advanced code reader the heater will produce trouble codes. I don't know why or how the MPH is effecting your heat. What is the outside temperature when this is happening.


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## roadhawg (Apr 24, 2017)

On the way home from work tonight it was 28 F. Engine temp was steady at mid gauge. The defroster would barely keep up with the freezing drizzle on the windshield.

I think engine speed and load is affecting the temperature fluctuations.

I'll stop by my local mechanic and see if he can pull any codes. I haven't found any dealers that can be trusted to work on this car. I've tried three.


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## Tomko (Jun 1, 2013)

roadhawg said:


> Does anyone know how to troubleshoot this heater ? Is it accessible through the glove box ?
> Not getting much heat under 40 mph, but getting a good amount of heat at 60 mph +.
> 
> I don't think I'm getting any "Reinforced Electric Heating".
> ...


The electric heating element only engages when the heat is turned all the way to the absolute maximum setting. 

Fan speed will also affect the amount of heat that can be drawn from the electric element and heater coil. The slower the fan setting the greater the heat can be extracted from those two sources. 

The second fan setting works just fine for me - and occasionally the third. But never anything more than that.


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## boraz (Aug 29, 2013)

roadhawg said:


> On the way home from work tonight it was 28 F. Engine temp was steady at mid gauge. The defroster would barely keep up with the freezing drizzle on the windshield.
> 
> I think engine speed and load is affecting the temperature fluctuations.
> 
> I'll stop by my local mechanic and see if he can pull any codes. I haven't found any dealers that can be trusted to work on this car. I've tried three.


if coolant temp gauge is at middle (like 6 oclock right? thats essentially full temp), the electric heat isnt on its only on until the coolant warms up

does your ac cool? defrost works best with operational ac to pull the moisture, maybe your ac isnt 100%


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## justin13703 (May 2, 2016)

boraz said:


> if coolant temp gauge is at middle (like 6 oclock right? thats essentially full temp), the electric heat isnt on its only on until the coolant warms up
> 
> does your ac cool? defrost works best with operational ac to pull the moisture, maybe your ac isnt 100%


Even on defrost, will the ac compressor even run in sub freezing temperatures? I know on my truck, when the ambient air temp is below like 40 degrees the ac compressor won’t turn on, no matter what you do. Not sure if the Cruze is like this or not.

Plus, if the problem is that it’s not melting ice on the outside of the windshield, it doesn’t really matter what the ac is doing, it sounds more to me like a temp problem with the air leaving the vents. The ac on defrost mainly prevents condensation on the inside of the windshield, but doesn’t do much about the outside.


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## Cruzator (Dec 31, 2014)

The compressor does shut off as temperatures get cold (I'm guessing between 40 and 45 degrees F). The aux, electric heat shuts off when coolant temp get up to 170 degrees. Have you monitored your duct or defrost temp? Mine easily gets hotter than 160-170 degrees with an ambient temp in the 20's.


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## roadhawg (Apr 24, 2017)

The mechanic spent 1.5 hours troubleshooting this thing. Some of the things he thought were causing the problem:
- Thermostat, it took 40 minutes to warm up idling in his shop. I think this is normal, usually takes about 10 minutes driving time to warm up.
- Slightly low on coolant. No leaks found.
- Code for heat strip inop, c67, I don't think he wrote down the right code.

The one that made the difference was :
- *Blend door* stuck at 81 degrees, per advanced diagnostics. He rotated the temperature knob back and forth several times and it started moving, angles displayed on his diagnostic tool..
He left the knob in the fully clockwise position and I haven't touched it since. Now the electric heat is working while the car warms up, and i have plenty of cabin heat when the engine reaches it operating temp. The ice melted off of the windshield this morning with ease.

I'm not touching that knob until heater season is over. I'm not looking forward to tearing the dash out to replace a blend door actuator.


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## dougc905 (May 24, 2015)

roadhawg said:


> The one that made the difference was :
> - *Blend door* stuck at 81 degrees, per advanced diagnostics. He rotated the temperature knob back and forth several times and it started moving, angles displayed on his diagnostic tool..
> He left the knob in the fully clockwise position and I haven't touched it since.


Interesting that there would be feedback about the blend door!


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## justin13703 (May 2, 2016)

If he just left it idling in the shop, yeah they will take forever to heat up. Nothing is wrong there. They just don’t produce much heat at idle. The Cummins at work, if we tried to let that thing come up to temp by idling it, it would probably take at least 2 hours lol

Sometimes those actuators that control the blend doors on new cars can kind of get out of position and when they do they will do strange things. My Dodge does this from time to time. Usually cycling it from one extreme to the other will take care of it.


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## 91794 (Mar 25, 2015)

after -15F cold morning cold starts the car warms up reasonably at idle. Impressive. 

The supplemental electric heater is *awesome*, very very noticeable and helpful, especially when combined with bunwarmers and heated steering wheel.


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