2005 XC70 interior blower fan won't turn off (at all) and ultimately kills battery

For the past three days the interior blower fan will not turn off after shutting off the ignition, ultimately it runs all night and the battery dies and must be jump started. It's not the fan associated with the engine or radiator but a cabin fan of some type. I know that there is a built-in fan that can run for 5-6 minutes by design after you turn the ignition off and that this is normal, but that is not what is happening, it will run for hours and hours. Nothing basic has worked, such as starting the ignition and turning it on/off several times. It seems that the fan is running at a very low mode, but regardless if just never turns off.

Trying to prevent having to take it to the dealer and spend hundreds if there is a self-serve solution to this problem. Any advice on what to try from those who have come before me ?

The blower motor and transistor power unit need to be replaced. Usually the blower failing and being bound up enough to draw more current will overheat the transistor circuit and it fuses conductive parts. The blower has 12v+ feed all the time and the power unit is the ground. When the power unit fails it is grounding the motor to operate it when there is no signal from climate unit.

Unfortunately our rig seems to be experiencing a simlar problem. I can usually get the blower to quit when I pull the 30A Climate Control System Fan fuse. Might help save your battery while you are working through cattlecar's solution.

In addition to blowing for hours at both low and high speeds when the igntion is off, our rig will blow at high speed when the ignition is on and no button or control will adjust the speed. Also (usually only after driving for a few hours on the highway) the blower fan will not blow at all, again regardless of how the controls are manipulated. Am I too looking at a blower motor / transistor power unit replacements? Or do my additional symptoms suggest another ailment?

Thanks in advance for your assistance.

If the fan regulator transistor unit fails, it will most probably always show the same behavior,
either always blowing ful speed, or not blowing at all. If the fan sometimes blows and
sometimes not at all, I think the problem may be something else than the regulator.
The regulator (power unit in Vadis) can be replaced seperately, contrary to the engine fan
where fan and regulator are one assembly.
The best thing you can do to prevent the regulator unit from failing is to replace the cabin
filter in time. When the filter gets clogged, the fan needs to work harder, the regulator gets
hotter and its cooling becomes compromized.
Should you try to replace the power unit yourself, I can post a few pdf's describing the job
and a parts list of the fan and regulator unit.
Willy

My previous statement that the power unit can be replaced seperately may be wrong since I referred to
XC's until MY2004 and the problems in this topic occur in more recent models.
I also don't have a Vida version of Volvo's workshop manual running at this moment so I can't verify it.
But since I am not aware of any changes concerning the interior fan I think it may be useful to post the procedures.
The attached pdf pages show the removal of the complete fan assembly and the power unit itself for cars until MY2004.
Willy

Took advantage of some extra time onver the Labour Day weekend to replace the power-unit. Looks like this was the culprit climate blower systems seem to function normally and the fan has not continued running after the ignition has been shut off for 6 days now.

Thanks for your help Willy!

In addition to the PDFs you provided I also found the following forum useful:
http://www.volvoxc.com/forums/showth...g-battery-Help!

And this forum on another site:
http://www.matthewsvolvosite.com/for...hp?f=9&t=21343

The replacement should have only taken me an hour or so, but one screw on the blower fan housing was a pain in the %#* to get out ... will have to get myself a flexible screw driver as I'm sure that would work much faster and simpler than a T25 bit aligned at just the right angle in a pair of vice-grips.

I recalled replacing a very filthy cabin filter shortly after we got the rig - so I figured Willy's advice must have been bang on... power unit replacement solved the issue. It has been two weeks and all climate control systems appear normal. All blower fan controls function and the fan shuts off when the ignition is turned off.

Thanks again for your help Willy!! [thumbup]