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AC is ON even when selected to OFF?

AndreyATC

Member
Dec 19, 2013
541
152
Cape Coral FL, USA
Hello all
Temperatures have been on a low side for a while
I usually turn on a fan to circulate air
however I noticed that when the fan is on the AC kicks in as well
no matter what I do I cannot turn it off
I can understand if this was an auto setting but this is a manual override when I turn it off
example:
outdoor temp 64f, car setting 72f, cabin temp is 75f
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,028
1,025
I contacted Tesla about this. The car monitors relative humidity and will activate the compressor when the humidity gets too high to prevent window fogging, even when the setting is "A/C off". I was told this is intended behavior.
 

jerry33

(S85-3/2/13 traded in) X LR: F2611##-3/27/20
Supporting Member
Mar 8, 2012
20,117
25,398
Texas
I contacted Tesla about this. The car monitors relative humidity and will activate the compressor when the humidity gets too high to prevent window fogging, even when the setting is "A/C off". I was told this is intended behavior.

Other cars do this same thing. Normal and expected.
 

Electric700

Active Member
May 21, 2013
1,758
435
Florida, United States
Also if the battery requests cooling for optimal efficiency, the compressor will turn on. As a result, my guess is that you may experience a cooling benefit even with just the fan on.

Still, most of that cooling is going toward the battery. Other cars like the Chevrolet Volt (which has a battery cooling/heating system also) work this way too.

Consider using the heated seats or increasing the cabin temperature if you're too cold.
 

scaesare

Well-Known Member
Mar 14, 2013
8,577
15,165
NoVA
My issue is that often I'd like to have outside temperature fresh air thru the vents... particularly in the spring and fall. Even when there's not sufficient humidity to come even close to fogging the windows, it will enable the A/C. And if the window-vents are enabled, the compressor remains on the entire time.
 

andrewket

Well-Known Member
Dec 20, 2012
5,704
1,541
Also if the battery requests cooling for optimal efficiency, the compressor will turn on. As a result, my guess is that you may experience a cooling benefit even with just the fan on.

Still, most of that cooling is going toward the battery. Other cars like the Chevrolet Volt (which has a battery cooling/heating system also) work this way too.

Consider using the heated seats or increasing the cabin temperature if you're too cold.

This was true for the roadster but I don't believe true for the S. The S has independent cabin and battery cooling systems.
 
Last edited:

scaesare

Well-Known Member
Mar 14, 2013
8,577
15,165
NoVA
This was true for the roadster but I don't believe true for the S. The S had independent cabin and battery cooling systems.

Sort of. The A/C subsystem is common to both, but can selectively loop the battery and cabin in or out of the chain.
 

theapple

Member
Oct 15, 2013
20
1
Massachusetts
I've noticed the same, but I was under the impression it only happened when the AC kicked on to cool the battery; I can feel it cycle on and off, usually because it gets unpleasantly cold, but it behaves most of the time.

Far, far worse in my opinion is that the 'recirculate' setting also has a mind of its own. It likes to switch to fresh air while you're following a diseasel truck, and also in the winter, when doing so causes it to gobble up precious battery capacity to heat the -10 degree outside air instead of the 70 degree cabin air. This is my only real gripe with the car, but it definitely annoys the heck out of me.
 

AndreyATC

Member
Dec 19, 2013
541
152
Cape Coral FL, USA
My issue is that often I'd like to have outside temperature fresh air thru the vents... particularly in the spring and fall. Even when there's not sufficient humidity to come even close to fogging the windows, it will enable the A/C. And if the window-vents are enabled, the compressor remains on the entire time.
+1
i'd like to be in control of the whole system
it doesn't make sense when the car decides when to turn on the AC compressor
if it gets foggy I can just press the button, what's the big deal?
I actually don't remember having this "future" with previous firmware
 

mknox

Well-Known Member
Aug 7, 2012
10,103
1,894
Toronto, ON
I have not seen this behavior, and it gets pretty stinkin' humid around here. In my case, the a/c compressor will only kick in (if set to off) if I select defrost mode either alone or in combination with another vent setting.
 

scaesare

Well-Known Member
Mar 14, 2013
8,577
15,165
NoVA
Assuming by "defrost" you mean specifically enabling the separate button on the main lower button bar (not the popup panel). If so, try this:

Set the A/C to off, and then enable all the vents. Set the temp to "Lo" (so that there's not potential for the heater to kick in).

Observe the air coming out the vents is colder than outside ambient.
 

Lloyd

Well-Known Member
Supporting Member
Jan 12, 2011
6,335
2,205
San Luis Obispo, CA
I believe that if the temperature of the battery is above the active cooling target, the AC will kick on, and some of the cooling will be ducted to the cabin if the temperature inside calls for cooling. Not verified, just MO.
 

FlasherZ

Sig Model S + Sig Model X + Model 3 Resv
Jun 21, 2012
7,028
1,025
This is the response I received:

With regards to the A/C question you had, after manually turning off your AC, the cabin humidity levels reached 75%. At this level, the windshield is in danger of fogging, which resulted in the A/C running every so often to prevent the fogging.
 

mknox

Well-Known Member
Aug 7, 2012
10,103
1,894
Toronto, ON
Assuming by "defrost" you mean specifically enabling the separate button on the main lower button bar (not the popup panel). If so, try this:

Set the A/C to off, and then enable all the vents. Set the temp to "Lo" (so that there's not potential for the heater to kick in).

Observe the air coming out the vents is colder than outside ambient.

Yeah, either hitting the discrete Defrost button OR selecting defrost on the pop-up panel would result in the compressor kicking in. When you say "enable all the vents" I assume that would include the defroster vent, and as I say, it WILL kick in if the defroster vent is selected.

Have you seen the a/c kick in if the defrost vent is NOT selected? By that I mean either floor or dash or both floor/dash vents. I have not personally seen that happen.

Having the a/c compressor kick in whenever the defrost vent is selected is consistent with other vehicles I've owned in the past, but having it kick in when only the other vents are selected, and a/c is switched off, is not.
 

scaesare

Well-Known Member
Mar 14, 2013
8,577
15,165
NoVA
Yeah, either hitting the discrete Defrost button OR selecting defrost on the pop-up panel would result in the compressor kicking in. When you say "enable all the vents" I assume that would include the defroster vent, and as I say, it WILL kick in if the defroster vent is selected.

Have you seen the a/c kick in if the defrost vent is NOT selected? By that I mean either floor or dash or both floor/dash vents. I have not personally seen that happen.

Having the a/c compressor kick in whenever the defrost vent is selected is consistent with other vehicles I've owned in the past, but having it kick in when only the other vents are selected, and a/c is switched off, is not.


I have other vehicles where if the A/C was disabled, i could get fresh air from the windshield vents without the A/C kicking in.

My preference would be for the the "defrost" main panel button to be a "quick preset" that enables windshield vents, turns on A/C, selects appropriate recirc settings, etc...

However when I manually over-ride settings on the sub-panel, I'd like the car to honor that.
 

mknox

Well-Known Member
Aug 7, 2012
10,103
1,894
Toronto, ON
However when I manually over-ride settings on the sub-panel, I'd like the car to honor that.

I agree, and come to think of it, even on my past cars that did turn on the compressor in defrost mode, I could hit the a/c button and turn it right back off again. (I wonder if that works with the Tesla... it would be at least a workaround to using the defrost vent without the a/c running)
 

scaesare

Well-Known Member
Mar 14, 2013
8,577
15,165
NoVA
I agree, and come to think of it, even on my past cars that did turn on the compressor in defrost mode, I could hit the a/c button and turn it right back off again. (I wonder if that works with the Tesla... it would be at least a workaround to using the defrost vent without the a/c running)

Interesting idea worth testing...
 

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