Hello! Voltage Drop when i turn off the heater

[Mordan]

Hello and Merry Christmas!

Just a quick advice.

My heater(basic version no AC) stopped working unless on position 4 and then Battery Voltage drops to zero.

Problem is not the Voltage Regulator.

Why would a current consumable in the car drop Voltage to near Zero and sometimes going back up to 10V?

Cheers!

EDIT: Error in title "turn on"

[John in CT]

Merry Christmas Mordan;

The climate control circuitry is about as complicated as the Space Shuttle. There is a fan controlling device called a "Sword" that may be related to your troubles. Shogun has written the following troubleshooting guide but unfortunatly it looks like you have to dis-assemble about half of the interior of your car.....

Behr sword MOSFET, Siemens sword (http://www.bimmerboard.com/forums/posts/136145)

Good luck,

John

PS; Well not really half but here is the proceedure for E32, ours are not real different.

http://www.meeknet.co.uk/E32/Microfilter/Index.htm

[myles]

The heater/fan unit with no a/c is a very simple unit by comparison to the ihkr and ihka units that we see with air conditioning. The logic circuit is all contained within the switch panel and a simple resistor pack.

I've never seen a wiring diagram for the heater unit, but it couldn't be too hard to pull the switch panel and the resistor pack and start testing with a multimeter. Don't forget to test the resistance of the blower motor.

The system is otherwise controlled with cables.

[ss2115]

Hello and Merry Christmas!

Just a quick advice.

My heater(basic version no AC) stopped working unless on position 4 and then Battery Voltage drops to zero.

Problem is not the Voltage Regulator.

Why would a current consumable in the car drop Voltage to near Zero and sometimes going back up to 10V?

Cheers!

EDIT: Error in title "turn on"

Does the same thing happen if you turn on the headlights? (ie: something else with a big current pull).
If so, it may be your battery with a weak/dud cell, or a poor battery connection.
I would also look at the battery connection on the back of the alternator, and also the earth lead(s) between engine and chassis.
Lastly, test the charging voltage and current from the alternator under load and no load situations.

[Mordan]

when i turn on the headlights, voltage drops to 13.5 so i think it is acceptable.

[genphreak]

The in line fuse on the smaller red wire about 8" from the positive terminal of the battery (assuming it is a model that has the battery under the back seat) is intermittently causing problems. The blower is the main consumer of power on this circuit- except for the windscreen wipers. Maybe you can test to see if they only work on maximum sometimes and/or perhaps cause the same symptom you describe.

The fuse actually wears out- I think there is invisible corrosion in the riveted joints, the only fix is to replace the fuse- messing with it will not work out!

It is 50 or 80A I can't remember which...