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General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 09-15-2016, 07:37 PM   #1
Barry Beamer
Registered User
Join Date: Jul 2015
Location: Gippsland
Posts: 7
My Ride: e46
Power loss when air-con is on

Hi Team,

My 1999 E46 5 speed manual has now developed a problem where the power basically cuts out when the air-con is turned on. When the air-con/fan is off it runs very smooth, but when its on it will backfire and get to about 2000rpm in second and then its like you took the key out of it. You have to wait till it stalls and then start it again. If you can get the revs stay above 4000rpm it seems ok, but as soon as you change gears downwards it will cut the power out again.

Strangely, at the same time this happened the temperature gauge started playing up, and will swing all the way to hot, then slowly drop back to normal temperature.

The start up lights on the dash to the left hand side of the odometer have also stopped working.

My mechanic has disconnected the air-con wire so the car is running ok, but the temp gauge is still swinging all over the place and the start up lights are not working. He replaced the air flow metre etc etc but wasn't until he discovered the connection between the fan/air-con and the power that we could work out why the power was cutting out.

Does anyone have any ideas about how to fix this, or encountered anything similar? We are at a bit of a loss as even the main BMW distributor here in Australia has not heard of this happening before!

Thanks if anyone has any thoughts.

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Old 09-16-2016, 04:51 AM   #2
Registered User
Join Date: Aug 2011
Location: oregon
Posts: 478
My Ride: bmw 325i
The ac is tied into the idle circuit so I would trace the wires through a diagram and then locate certain, spots where the harness may be damaged.
A mechanical hobbyist and car enthusiast
1971 Datsun 240z Devil Z red
1999 740il Titanium Silver
2004 BMW 325i CW,PP and Sports Package
1996 toyota avalon-263,000-Sold
2003 Lexus Is300-Sold
2000 Acura TL-Sold
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Old 09-16-2016, 07:16 AM   #3
Barry Beamer
Registered User
Join Date: Jul 2015
Location: Gippsland
Posts: 7
My Ride: e46
Thanks Loaded325i. The idle has certainly been rough and we could never work out why. We replaced a few thousand dollars worth of parts and it was still no good. Your tip could unlock the answer! Thanks so much I really appreciate it!
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