[beachmiles]

If it is a significant use of energy They will get around to cutting off the heater. It may be that the hvac cooling system isn't able to be variable. In that case, it would cycle on and off continuously. I have to think Tesla did a cost/ efficiency analysis and we are where we are. iows it cost more than they wished to
spend for not enough energy savings.
I would think the constant on-off cycling would be effective for what you want, but there might be an issue with sustainability.

You sir sound like a gentleman and a scholar. Maybe that was Teslas concern of wearing out some part/ball valve trying to throttle the cabin AC on and off all the time vs just leaving it on and using the cabin heater to "set" the temp. Or maybe like you said they have bigger fish to fry, but in certain climates/driving styles this fish may be 5% increased power usage. I need to get that CAN setup going to / my own current sensor to verify my estimated power savings. I think this also explains why some people feel hot air coming out when they expect only cool AC to be operating.

 

[beachmiles]

Just did a quick test with my dc amp meter clamp on one of the power cables to the cabin heater after reconnecting the CAN connector to the cabin heater after a failed software update which later worked after I reconnected the CAN connector.
Anyways It was only 72 outside with a cabin temp of 73 according to the app and I set the temp to 71 with recirculate on in manual mode.
No current showed on the meter until the inside temp went to my set point of 71.
Then the current started bouncing between .50 and .60 amps continuously, seemed to stick around .57 amps. That's about 200 watts at 350V... not chump change as far as wasted power in my electric car.
So leaving the AC on def uses the heater when it's hotter outside the car. Thats about 15 100watt equivalent LED bulbs I accidentally left on while running my car off a battery.

This doesn't take into account the extra power draw from the AC running all the time while fighting the heater.

 

[JWardell]

Just did a quick test with my dc amp meter clamp on one of the power cables to the cabin heater after reconnecting the CAN connector to the cabin heater after a failed software update which later worked after I reconnected the CAN connector.
Anyways It was only 72 outside with a cabin temp of 73 according to the app and I set the temp to 71 with recirculate on in manual mode.
No current showed on the meter until the inside temp went to my set point of 71.
Then the current started bouncing between .50 and .60 amps continuously, seemed to stick around .57 amps. That's about 200 watts at 350V... not chump change as far as wasted power in my electric car.
So leaving the AC on def uses the heater when it's hotter outside the car. Thats about 15 100watt equivalent LED bulbs I accidentally left on while running my car off a battery.

This doesn't take into account the extra power draw from the AC running all the time while fighting the heater.

I'm not sure a clamp meter will get a reliable reading if any if the wires are shielded, as they hopefully are being high voltage and needing the extra layer of safety. I do think we can read CAN data though. I did some specific tests with heat off and on, I will have to go through them to see if I can find actual heat currents.
You can easily do with with no tools though, by looking at the current when plugged in but not charging...the car will draw the same power from the wall as it is sending to the heater.
The heater will draw about 8000 watts (20+ amps) when cold and under full power, though I do believe it is fully variable.

 

[JWardell]

Well, here's the proof in the pudding! Here's a drive I made on a warmish day in September, and you can see I start with HVAC on, and you see ~1000W of heat used while just keeping the cabin around its set point of 21C. I turn off HVAC and you see the compressor and heaters turn off. I open the window and you can see the interior temp start rising. Halfway through I turn the HVAC back on and soon after the heat starts ramping back up as the cabin is cooled.
Then you see that huge spike at the end...I purposely cranked the heat to Hi and fan to max, and you see it ramp to 3350W per side...6700W total.
I'll add these to my DBC file so others can do their own sleuthing.

 

[beachmiles]

Well, here's the proof in the pudding! Here's a drive I made on a warmish day in September, and you can see I start with HVAC on, and you see ~1000W of heat used while just keeping the cabin around its set point of 21C. I turn off HVAC and you see the compressor and heaters turn off. I open the window and you can see the interior temp start rising. Halfway through I turn the HVAC back on and soon after the heat starts ramping back up as the cabin is cooled.
Then you see that huge spike at the end...I purposely cranked the heat to Hi and fan to max, and you see it ramp to 3350W per side...6700W total.
I'll add these to my DBC file so others can do their own sleuthing.

View attachment 30526

Awesome data, it looks like its 1000w used by both driver and passenger side cabin heater so that would be 2000w total power used heating the car when it's hot outside right?

In any case that's a lot of lightbulbs being left on accidentally. Unless there is some fear of wearing out the actuator that turns the cabin AC on and off this seems like some very low hanging fruit to increase the range if you have the AC on and you are only trying to cool the cabin and not heat it.

 

[brur]

OP, have you been reading the "heater" thread over at Tesla Motor Club? Last post mentions pulling the connector to heater- saved him considerable energy.

 

[beachmiles]

Here is a quick vid I made on how to unplug the CAN connector to the cabin heater

 

[beachmiles]

Posted the link on Reddit only to get savagly attracted. Please upvote if you get a chance.

 

[beachmiles]

Did another test with my DC current clamp meter in the right position this time on and was seeing a steady 1-1.6kW pulled from the cabin heater. It was 67 outside with a 66 degree setpoint with the car having been parked for a couple hours. Will try to do another test again after the car has been driving for a while in 75ish temps, and another with 90ish temps to see what kind of diffs I get. I need to get the CAN interface setup!

 

[EchoCharlie3189]

I've been trying to trick heat off as well by running outside air up the windshield to keep it from fogging. If I set the temp to LO with A/C off and my seat heat on max, I still get too cold with the fan on 1.

I've been resorting to setting it to 18 or 19 degrees C (when I normally do 20-21 for comfort) and letting the fan modulate with A/C off and it seems to control humidity while just being on the cold side of comfortable.

Thanks for all of the research on this front, I might unplug my heater next summer if they don't come out with a heat button by then!

 

[nobrien1]

I have a basic question about how heating should work. I typically set my car to 67 degrees in cooler weather. With the temp outside well below that and the car not heated up, and HVAC on Auto, I have cold air blowing on my through the dash vents. Should that be happening? It's not comfortable!

 

[EchoCharlie3189]

I have a basic question about how heating should work. I typically set my car to 67 degrees in cooler weather. With the temp outside well below that and the car not heated up, and HVAC on Auto, I have cold air blowing on my through the dash vents. Should that be happening? It's not comfortable!

Does the air eventually warm up? Mine takes a little bit for the heating elements to reach temperature and make the air warmer. You can turn A/C off as well just to test if it has an effect.

 

[nobrien1]

Does the air eventually warm up? Mine takes a little bit for the heating elements to reach temperature and make the air warmer. You can turn A/C off as well just to test if it has an effect.

The car does warm up but it continues to blow cool air through the dash vent. If I boost the temp to 70 it stops and the car becomes decidedly warm. Turning the air off doesn't seem to change things. And, with 'automatic climate control', I shouldn't have to do that.

 

[android04]

If the plug that controls the heater has 4 wires and uses a CAN signal, then the wires might be CAN-H, CAN-L, ground, and 12V. If you want to easily enable/disable the heater you can put a toggle switch inline with the 12V wire and mount the switch in an easy to reach place under the dash or on the center console side panel.

 

[beachmiles]

Ya i think that's the simplest fix until Tesla lets us control the heater via their software.

I got the scanmytesla setup and verified my current clamp meter measurment from the cabin heater when just trying to cool the car was not a fluke and roughly the same current draw I measured was shown on the scanmytesla app. Although only 1/2 of the heater wattage values ( right or left side heater I can't remember) appeared to show good results with the scanmytesla app do to some api changes I guess. But that one side of the heater showed half of the wattage I was measuring with the meter so I feel confident this is not just in my head.

 

[EchoCharlie3189]

Ya i think that's the simplest fix until Tesla lets us control the heater via their software.
.

So I'm thinking about doing this to save some energy this summer but have you lived with it day to day? The error message would be annoying but acceptable, my only concern is the system might be oversized and will not run long enough to dehumidify the air. If it cools it down to 68 quickly then it doesn't have time to dry everything out before people in the car get too cold.

While I don't like burning more energy than I have to, reheat on the air might be necessary in the humid summer.

 

[beachmiles]

So I'm thinking about doing this to save some energy this summer but have you lived with it day to day? The error message would be annoying but acceptable, my only concern is the system might be oversized and will not run long enough to dehumidify the air. If it cools it down to 68 quickly then it doesn't have time to dry everything out before people in the car get too cold.

While I don't like burning more energy than I have to, reheat on the air might be necessary in the humid summer.

I drove with it off every day for about 3 months this past summer with no humidity issues / window fogging, but as it got closer to fall/winter when I left work late at night the windows would get fogged up so I would have to reconnect heater to defrost.

The humidity here in the LA desert is generally comfortably low humidity so your results may vary.
To mitigate the fact that the car would continue cool the cabin I put the fan to the lowest setting and moved the vents up and away from me and enabled the rear vents. I would have to toggle the AC off/on generally once per trip as it tends to just get too cold inside when its boiling outside ( 90F outside, temp setpoint is 80F/HI, and inside it gets close to 62F). But once I turned the AC off it only took like 5 minutes for the interior to shoot way up so I would have to re-enable.

So its kind of a pain in the ass but if you have no home/workplace charging or if ever find yourself trying to make the next supercharger when its boiling outside you can keep cool while increasing your range by about 5%.
Also if for some reason the car is not cooling down fast enough this mod feels like it doubles the AC ramp down speed without having that stubborn cabin heater fighting you.