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I bought a used Mini cooper countryman 3 years ago. Since I've owned it when the weather hits around -5 degrees F and I cold start the car, the heater won't work properly. The dash says it's slowly building up blower speed as the engine warms up but nothing is actually coming out the vents. When the weather warms up to around 5 degrees it miraculously starts working again. If I let the engine warm up I'll get residual heat coming from the vents to thaw the windows, but no actual blown heat. If I try and drive it like this the windows often frost up obstructing my vision. When the car eventually runs long enough to warm everything up (2 hours or more) the heater will start working. I've talked to the dealership a couple times and every time they've said it's a battery issue, in the cold the battery strength is lower than it normally is in warm weather and the car shuts parts of the car down to save electricity. I've had the battery tested and they say it's in perfect shape.

I'm told it has some sort of an alternator style battery that slowly charges the battery as needed, and I'm hitting some sort of sweet spot where it's doesn't charge enough to allow the heater to work, but not enough to realize it's a problem. They suggested installing a trickle charger which for the first couple of years I didn't have consistent power to plug into. Too many roommates had to park down the street. New living circumstances, I can now plug it in every night, but it's getting cold again and still no heat. I don't think it's the blower, thermostat, or anything like that (I wouldn't say I'm even close to a mechanic however). In warmer conditions everything works perfectly. Any suggestions on What the problem could be, or even a work around. I'm thinking of trying a battery blanket, but the battery is in an enclosed spot that I'm not sure I can easily accomplish this so I'm hoping for a better solution.

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The battery "issue" as stated by the service department doesn't make sense to me either. If it has enough power to start/run your vehicle, it has enough power to operate the blower motor. If the system were smart enough to know you were having a power issue, I believe it would be smart enough to tell you about it as well ... it could easily be incorporated into an OBDII code, or a warning on the dash of some kind. Again, this makes no sense to me.

You need to check to see if there is power going to the blower motor when this problem occurs. For your vehicle, the blower motor should be under the dash in the passenger's foot well. It should be covered by a shroud. Under the shroud, you should see something like the right side of this image sticking down:

From RockAuto.com

Pull the power lead which has the two wires. Check to ensure one wire has power and the other side is able to ground. You'll need a multi-meter to do this. To properly check this, the vehicle must be on with the dash showing the blower should be running. If your test indicates there's no power, the problem lies in the control itself. If there is power, the problem lies in the blower motor. At this point, with the plug unattached, you could apply power directly from a 12vdc source and see if the blower motor is energized. This would confirm there's no power getting to it from the controls. If it is determined to be the controls, about the only way to fix this would is replacement of the control itself. Why the cold would be causing this is beyond me, but I've seen crazier things go wrong.

If there is power, the problem may reside in the blower motor. If, for some reason, the blower motor freezes up (say, the lubricant has an issue), it will no longer work until it is warmed up. The blower motor resides outside of the heating loop (where the air flows) so it doesn't overheat while in operation. This wouldn't allow the motor to warm up to the point of working, either.

To check and see if this is the issue, locate the blower motor itself (see above). Take a hair dryer or heat gun and heat it up the bottom of the blower motor. If it starts to work after getting fully warmed, my suggestion is to replace this.

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