Blower Motor Problem is driving me nuts
This is for a 2011 Volvo XC90
About a week ago I started having problem with my blower motor.
The first time I noticed something wrong I started the car but the motor wouldn't blow. I drove for about 30-45 minutes and it started working. This was in the late afternoon so the hottest part of the day. Then a day or two later it just stopped.
I replaced the motor itself last year about this time but I was too cheap to replace the resistor. So I hoped it was the obvious thing and went ahead and replaced the resistor and everything worked fine. I drove it for about 4 or 5 hours overnight but then it stopped running again.
The next night (I'm in Texas and it's too hot to work on during the day) I checked the cabin air filter and it was filthy so I pulled that out, vacuumed a bunch of junk out of the duct but the fan still didn't run. Assuming maybe some junk had gotten to the fan I pulled I out again. I didn't see any junk but the fan did run just fine while it was out. I put it back in and it ran fine. Drove it again overnight (I drive Uber) and it ran fine until the morning. I stopped at the store and when I got back in and started the car the fan wouldn't start. (I had stopped and started the car a few other times throughout the night)
So the next night I checked it and it still wouldn't start so I pulled it out to check for junk and debris, nothing but as usual it would start when it was not installed. I put it back in, it still worked but only when I manually selected the fan speed, if I hit auto it would not work. So I used the manual speed and drove all night. About for or five hours into it noticed the fan was blowing a lot slower even though the dial was on high. I moved the dial back and forth and the fan went back to high. About an hour later it did the same thing but when I moved the dial the fan died.
I did a little more troubleshooting because I'm getting pretty sick of taking the fan out so I got out a multimeter and verified that the fan was getting voltage and the resistor was passing full voltage when the fan was set to high and lower voltage when it was set to lower speed so it seems the resistor is working ok. The control panel seems to be working ok. All the lights and controls seem to be working as expected. When I change the air source or air route I hear and see the right things moving and everything seems consistent except the blower motor.
I noticed that the large black and red wires still had full voltage even when the key was off, I assume that has something to do with the condensation protection it has. So I thought maybe disconnecting and reconnecting the power while removing and replacing was doing something. I unplugged it and left it for several hours, but no luck.
I also tried the old resistor and it seems to have the same functionality as the new one.
When I went to pull it out again I loosened the screws just enough to reach in and touch the fan cage and I was able to verify that it moved freely. I turned the key on and set the fan control but the fan didn't do anything. So I finished pulling it all the way out, without unplugging it this time, and it ran just fine.
So it seems like something is resetting it when I pull it out because it runs just fine but then dies after four or five hours. I have the fan out and sitting on the floorboard but running to see if it will eventually die and then I can check voltages and temperatures. Any other ideas?