W202 CDI Heater Booster Draining Battery

[David Pemberton]

Hello

Is the heater booster meant to draw current from the battery when the ignition is off?

I've been having problems with the battery on the car not having enough oomph to provide a cold start. At first I thought it was down to the (I think) original battery being at the end of its 8 year life. But a new battery hasn't fixed the problem so it was time to get the multi-meter out (which I couldn't do first time as I was 70 miles from home...).

Ignition off I get ~12.8V, engine idle 13.6V, 2000 rpm 14.0V, 2000rpm lots of electrical load on 13.5V. It doesn't seem to be a battery/alternator fault.

Current drawn when ignition off ~1.0A. Pull all the fuses one-by-one and it drops to 0.25A when the fuse for the heater booster is out. Engine cold and outside temp 4C so in the range where the heater booster would work. But surely it should only need to draw current when the ignition is on?

I'm not even convinced that the heater booster has been working for some time, perhaps even the last 30,000 miles during which I've owned the car. Warm-up isn't prompt and fuel consumption doesn't seem to vary much even when conditions mean that the booster should be working.

For now I've pulled the fuse for the heater booster and will leave it out until I get some inspiration.

Any ideas very welcome.

Best wishes

David

 

[Kallisti]

Well, I have no clue, but the above looks very wrong - I assume you've got a faulty unit.

On the same topic, how effective is the heater booster for people? Does it take the chill off, or does it actually put out warm air? Mine doesn't appear to do anything much at all (E320 Estate, W Reg W210)

 

[television]

Hi Dave, all of your figures seem rather on the high side 0.040 would be the normal max current when locked

 

[mattkh]

On the same topic, how effective is the heater booster for people? )

Hi
What is a heater booster ?

 

[Cnics]

The Heater booster is a ****** annoying thing that seems to be causing trouble on everyones cars and vans this winter.

its a diesel fueled water heater that heats the water to allow the engine and cab to heat up quickly on colder mornings, it works when external temp is below 5degreesC and cuts in and out to keep the engine at its normal operating temp, which for me is 85degrees.
The system does run on for a moment or so after you switch the engine off, but if its working right you should hear it running and then wind down so no current should be drawn after this point.

 

[David Pemberton]

Hi Dave, all of your figures seem rather on the high side 0.040 would be the normal max current when locked

Hello Malcolm

Thanks for current draw the data. I probably hadn't done a very good job of "turning the car off", e.g. it was unlocked, the tailgate was open (though the boot light out). And some odd things were happening such as the current going up when I pulled two of the fuses (can't remember which, radio might have been one), again suggesting the car didn't think it was "off".

So far, with the heater booster fuse out I've been OK. Now I know it can't work, I'm certain it actually wasn't working for the last 30,000 miles as I haven't noticed any difference!

Best wishes

David