Is it normal for the E-heat to come on with the AC?

jeffdawgfan

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My experience is that if you put it in max ac the e heat will turn off by itself.
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theo1000

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To clearify this, my point is that there are two systems, one being battery management, the other being cabin hvac, both sharing the AC compressor and the PTC element, the screen only selects what the HVAC system MAY use, the battery management overrides this.

There is ONE PTC heater element in the Mach-E. The E-heat button on the screen controls if it is used for cabin heating or not. It is not "the E-heater", E-heat is just a software thing on the screen, and enables the use of the PTC element for cabin heating.....

.....The confusion here is about the E-heat and A/C settings on the HVAC screen, which controls IF the system can use/turn on those based on requirement. It does not mean it is on, and both are not on/off, they can be regulated. Heater can be in several power modes, the AC compressor has variable speed. I have seen with outside temperature of 30C/78F that the whole car consumes about 800-900W of power parked for hours with A/C running for cabin cooling.
Thx for taking the time with your detailed post.

So the E-Heat is only for the Cabin HVAC control.
It turns on resistive heating during A/C for dehumidification. If you turn it off de-humidification stops. BMS can get heat as needed and is not affected.
It turns on resistive heating in winter for cabin heat. Higher temperature boost?
If you turn it off, in winter only the low grade heat from batteries will be supplied.

This is very close to how the Chevy volt was set up. Except I believe this is the flip between 'ECO Mode' and 'Comfort Mode'

Am I missing anything.
 

theo1000

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Great that that is your question, but why throw shade on @noway?? His post sure looked like it was, and has been since confirmed to be, right out of the MME shop manual. The forum member you mention as being the only one worth reading has on more than one occasion authoritatively posted things that are demonstrably false.
I had to use the 'show ignored content' button to see that post.
I'm sorry you see it that way but I understand. Personally I don't pay any attention to who posts what but try to understand what they are saying.

Note that it has been clarified that the post did not mean to imply that the E-heat button affected the BMS temperatures, which is what threw me off. You can see in the image he posted that the PTC heater raises the temperature of the refrigerant just enough to heat the cabin but then drop it back down to battery regulation temperature. This was not clear at all in his first post.
 

MachTee

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It does kind of bug me that when I press auto, E-Heat comes on, sometimes. However, I very much do appreciate that there's an E-Heat button that I can toggle off if I wish. One of the things that bugged me in the model 3 was that the only way to make sure the car doesn't run the e-heat, I'd have to tap tap TAP to change the temp to LO, if I just wanted some air to come in without AC or heat. The entire time I owned that car, I was manually controlling the climate control to maintain maximum efficiency. Simply leaving it on auto killed my Wh/mile. And that car was constantly fogging up. Constantly. I'll see how MME does when the weather is cool and damp, but it is doing much better so far.
 


noway

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Thx for taking the time with your detailed post.

So the E-Heat is only for the Cabin HVAC control.
It turns on resistive heating during A/C for dehumidification. If you turn it off de-humidification stops. BMS can get heat as needed and is not affected.
It turns on resistive heating in winter for cabin heat. Higher temperature boost?
If you turn it off, in winter only the low grade heat from batteries will be supplied.

This is very close to how the Chevy volt was set up. Except I believe this is the flip between 'ECO Mode' and 'Comfort Mode'

Am I missing anything.
In my experience, with non-freezing temperatures (will know in a few months) is that the batteries generates close to no heat during driving, but will generate heat during high power charging, but still does not seem to be enough. I have tried in pretty high temperatures, but low enough to require heating, to turn off E-heat, and result is always the cabin is cooling and no heat is generated from the batteries. So basically, if not high power charging a lot, there is no heat from the batteries to heat the cabin, it is just using the PTC heater.

It wants to keep the batteries between about 20C/65F and 35C/95F, and that is not enough to heat the cabin any significantly. This range is what I have seen by monitoring the temperature from OBD port. Since it does not use any heat pumps it will need to heat both the battery and the cabin to be able to use any heat from the batteries, it simply cannot get the temperature higher than the battery temperature from the battery coolant without using the PTC heater. But it still will be able to get "some heat" in the circuit by slowly circulating the battery (this is speculation from my part).

I would think that when driving and the outside temperature is high enough to not require heating it will never turn on the PTC heater, it will just circulate the coolant through the HVB and use the cabin heater core as a cooler (which is what the service manual say it does). In my experience it seems to turn on the A/C compressor and start aggressively cooling the battery when it reaches 35C/95F during charging, that is when cabin heating is not enough to cool the battery.

There was a software bug earlier which I think is fixed that was mentioned when testing was being done by press in Norway before customer cars was delivered. It was suggested to turn off E-heat while high power charging in cold temperatures, since that then implied it could use the PTC element for battery heating, and it would charge faster. It was supposed to be fixed by "turning off E-heat by default" when charging or something like that, which probably means it will not run the two circuit mode during high power charging. Since it is not technically possible to isolate the PTC element from the heater core it is not possible to "turn it off", just to not allow the cabin heater core to get priority by splitting the circuits.

When mentioning the Chevy Bolt. With Weber Auto channel as source for this, it seems to have a very similar system, and may be seen as the "previous generation" of what the Mach-E has. It just instead of the 4 way valve allowing heat to be transferred from the battery to the cabin heater by merging two circuits, it uses three circuits in total (the motor+electronics being the third, simiar to Mach-E). The cabin heating is a completely separate circuit and the HVB cooling/heating is very similar to the Mach-E, but will have its own PTC heater. The Bolt system cannot cool the battery by using the cabin heater core, so it will have to switch directly to the A/C refrigerant cooler if I remember correctly.
 

MachHI

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So I've been digging through the forum trying to find solutions to the issues that bug me most and this was one of the top.
Outside temp will be in the 90s inside temp set to 73 and the A/C blows hot air at me until I go into the A/C setting and shut off e-Heat which seems to come on every time I hit the Auto A/C button regardless of inside or outside temperature. It's annoying how much I have to fiddle with the A/C to make the cabin comfortable, about the only thing I'd be willing to trust the engineers about is that they are trying to give me heat stroke.

Is there a way to stop e-Heat from coming on? I live in the tropics and personally would be fine if it wasn't even an option.
 

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So I've been digging through the forum trying to find solutions to the issues that bug me most and this was one of the top.
Outside temp will be in the 90s inside temp set to 73 and the A/C blows hot air at me until I go into the A/C setting and shut off e-Heat which seems to come on every time I hit the Auto A/C button regardless of inside or outside temperature. It's annoying how much I have to fiddle with the A/C to make the cabin comfortable, about the only thing I'd be willing to trust the engineers about is that they are trying to give me heat stroke.

Is there a way to stop e-Heat from coming on? I live in the tropics and personally would be fine if it wasn't even an option.
Just leave it on and ignore it, it doesn't use that much power in the summer. I posted about this on the first page, but the reason E-heat turns on is for dehumidification. If you don't like that, then you will have to use manual control and never hit the AUTO button. When the dew point is above 70ºF I recommend using the recirc option to reduce the need for dehumidification. This will save more energy then shutting off E-heat in humid conditions. If you enter a hot car you may want to use the Max A/C function right away. I use Max A/C for a couple minutes if I didn't remote start the car ahead of time.
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