The blower fan in my 2008 Subaru Outback starts freezing up when it's about 0 degrees outside. After I drive it for 10 or 15 minutes, the blower comes on and works very well. 

 

Until it comes on, I can't defrost the windshield and it's pretty darn cold. 

 

I'm not sure if it's really frozen or what the actual problem is.

 

Note, I live in Fairbanks, Alaska, so we'll be seeing temps like this for the next several months. 

Simplest test is next time it does it smack the housing of the blower motor with a screwdriver handle. If it starts working, it's because the brushes are worn or stuck in the brush holders.

 

Sometimes the rear cover can be removed ( once the blower is out of the car ) and the brushes can be cleaned off with some electrical cleaner and a few shots of compressed air.

If the whole housing is sealed then you pretty much just have to replace the motor.

Sticking brushes like he said.

 

It's 100% repeatable like that every time - comes on after a few minutes or just happened like that one or two times?

 

I've seen some 05-09 models have clogged/linked condensation drainage lines and flood the interior. It's probably not possible for that water to get to the fan and you'd most surely see wet spots in the interior if it did. So I can't foresee that being an issue

could this be a cabin air filter issue?

It happens every time the temperature gets below single digits. Even if I warm the car up for 15 minutes, I still have to drive it a few miles before the fan will come on. Thanks for the tips -- I'll check the brushes.  

Makes sense.  Driving the car jars the brushes loose.

 

But, another thought:  Do the relays on these get flaky, like the ones on the Loyales?  Vibration from driving could kick a relay loose, too.

I've had this happen to 2 OEM blower motors on the same car. One was the original, and the other from a salvage yard. Same symptoms. At first, occasional failure to come on, getting worse with time. Tapping the motor as mentioned, or sometimes just hitting a bump would cause the motor to come on. I disassembled and cleaned both motors, and at first that helped, but finally the problem was permanent, and was worn brushes. I found two places to buy brushes. One set wore out in 2 days. Not sure if it was the brush material, or the commutator was too rough from wear. It may be possible to put the armature shaft in a drill press and polish the commutator with fine sandpaper/emery cloth, but I haven't done that yet on the other motor. I found that the aftermarket motors were all designed with the wrong mounting hole pattern for the 93 Legacy, so that's why I went with salvage yard. For my 93 Legacy, the brush size is .31x.31x.55" with a 1.5" shunt wire. I found them at Eurton Electric.

http://store.eurtonelectric.com/brushlowvoltage33e-2-1-1.aspx

 

Not sure if your motor uses the same size brushes. Check them with calipers.

You might find the commutator is so worn that by the time you polish it smooth, there's nothing left.

Maybe these photos will help, even though you are dealing with a newer Subaru. These photos are from my '93 Legacy.

The first shows the screws to remove to access the base of the motor. From what I have seen, aftermarket motors like the VDO brand from Rock Auto have no access point here

Next, what a dirty motor looks like.

Then, the commutator and worn brushes. Note the grooved wear on the commutator

If you decide to use new brushes, it is hard to remove the original brush pigtails from the crimp connections. it's easier to cut the original pigtails, leaving enough to splice in the new pigtail with solder.

I think the commutator needs to be polished smooth to prevent premature wear on the brushes.

Subaru Online Parts sells OEM motors if you need to do a genuine replacement.