Posts: 37
Joined: Mon Jan 07, 2019 12:45 pm

Heat pump? Best mode to "idle" in?

Tue Mar 12, 2019 12:00 pm

Can someone tell me if the B-Class uses a heat pump for cabin heating/cooling? I presume not, since I have seen no mention of it, but I've never seen it in a Tesla spec. either. I think the Leaf is the only car that owners brag about their heat pumps.

And if you're going to sit in the car and eat lunch, does it make any difference if the car is ready to drive or not? I mean you can pull up and just sit there, or you could switch the ignition key off and on, without going that extra step to "start" the car. I think in some cars the 12V battery provides power until the car computer activates the high-voltage. So I suppose I could be running down the 12V battery. If I get a chance to put a voltmeter on the 12V battery in both modes maybe I can tell.

In general I wish I could find a little more technical information on what's going on inside this car. No Haynes manual for us. :-(

Posts: 848
Joined: Thu Dec 11, 2014 9:12 am

Re: Heat pump? Best mode to "idle" in?

Tue Mar 12, 2019 6:45 pm


Ah, a fellow idler. I often idle in my B250e after I drive my kids somewhere. Better than sitting in some noisy coffee bar, plus I can make phone calls from the car using the super speakerphone. Not to mention listen to whatever I want on the radio, either sports talk or Spotify/Pandora. The seats are comfortable to boot.

For sure if turned off but COMAND system on, we are likely drawing from the 12V. But to get heat or ac with the ignition on but car not in gear, I assume we are drawing on the main battery given the AC/Heat requires a lot of juice. Sometimes I just leave it in gear, I don't think it makes a big difference that the intermediate stop if you are not moving. Maybe a few more systems on of course.

We have a member who owns in Edmonton, Canada, who will know the answer to your heat pump question. I knew the answer at one time but did not retain that nugget.

Good to see you back posting sir.
Jeff in NYC
MB '17 B250e; MB '06 E500W; MB '81 380SL

Posts: 37
Joined: Mon Jan 07, 2019 12:45 pm

Re: Heat pump? Best mode to "idle" in?

Wed Mar 13, 2019 9:48 am

So I had time to do a little detective work at lunch today. The "Smart key" ignition switch has 4 positions:

0 - OFF, The 12V battery voltage 12.3 V
1 - Some lights on dashboard, The 12V battery measures 12.1 V
2 - Ventilation fan on and more dash lights, 12V battery is now being charged at 15 V
3 - READY, Everything on and dash shows "READY", 12V battery being charged at 15V

So the two take-aways from this are:

- Never sit in the car with the key turned to the 1st position, you'll drain your 12V battery
- The 2nd and 3rd positions both charge the 12V battery from the High Voltage system so you can sit as long as you want.

And note to self... 12.3 Volts for a lead-acid battery under no-load conditions probably means I need to replace it!

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Joined: Fri Jan 25, 2019 12:25 pm
Location: UK

Re: Heat pump? Best mode to "idle" in?

Wed Mar 20, 2019 3:35 pm

My understanding is that the hvac system is powered from the traction (HV) battery, so you can have it working for hours with little battery depletion (you can watch the range indicator slowly reducing). However, the 12 volt battery powers all the domestic loads, such as lights, radio, wipers and navigation system etc. In order to stop the 12 volt battery from depleting you must have the ignition on; this powers the inverter, charging the battery from the HV battery. Never deplete the 12 volt battery as you cannot then turn on the ignition, meaning you are well and truly stuffed!

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