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E39 (1997 - 2003)
The BMW 5-Series (E39 chassis) was introduced in the United States as a 1997 model year car and lasted until the 2004 when the E60 chassis was released. The United States saw several variations including the 525i, 528i, 530i and 540i. -- View the E39 Wiki

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Old 01-22-2013, 10:19 AM
kgorczyn kgorczyn is offline
Officially Welcomed to the 'Fest
Location: Melbourne, FL
Join Date: Jul 2005
Posts: 337
Mein Auto: 2000 528i SP/PP
AC Will Not Engage

So my HVAC system has been acting 'funny' last few months. Sometimes when I start the car it doesn't work (it turns on and looks ok, but changing the fan speed, vents, temp, etc. does not work - it shows the changes on the LCD but does not apply them) - I turn off and on the car and then it's fine again.

Now however, I have a different problem that a restart will not fix.

HVAC Unit turns on fine, I can regulate the temp, all functions work, except the AC. When I press the AC button it turns green, but compressor does not engage, RPMs do not kick up. It's like it isn't doing anything.

Any ideas on what this can be? I reseated all the HVAC connections on the back of the unit, it did not help. I also disconnected the battery for 15+ minutes, did not help.

Last edited by kgorczyn; 01-22-2013 at 10:21 AM.
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Old 01-22-2013, 11:22 AM
DHoang's Avatar
DHoang DHoang is offline
Location: Austin, Texas
Join Date: Dec 2008
Posts: 1,097
Mein Auto: '98 528i, '82 323i
YOu may have a refrig leak.
THE A/C system needs a minimum amount of refrig pressure in order to
activate the clutch on the compressor. WIth a leak, your system pressure drops
too low to have the compressor working properly.
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Old 01-22-2013, 11:24 AM
Nervous Nervous is offline
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Location: Washington State
Join Date: Sep 2010
Posts: 571
Mein Auto: 01' 330CI 6MT / 00' 540i
Oh, man. This is a loooong story. Too many variables. I had a similar issue on my e46 and created this topic:

Even though it is for e46, most of the info is still relevant to e39.

Start with checking pressure in high and low ports using DECENT gauges. DO NOT ADD ANY FREON FROM EASY-TO-SCREW-UP-YOUR-COMPRESSOR kits from Walmart / Autozone / Advance / etc!
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