AC Blower Speed Slows Down On its Own When Set to High and Running Car for A While

Hey Everyone,

I have a 2006 Prius and lately, the fan will stop blowing hard on long drives on hot days when the fan is set to High. This happened on a 3 hour trip on the interstate and again when I was driving some back road for about 2 hours. The first time, I noticed the cabin temp was getting hotter so I went to switch the fan speed higher and noticed it was already on high. It was not set to Auto. When I got home, I let the car cool down for about 30 minutes and when I turned on the car, the AC was blowing full speed and was getting cold like normal. When the fan speed slowed down on its own on the interstate, it was probably blowing at a speed similar to what the fan would normally blow if set to the middle position or maybe even below that. I have no idea why the fan would slow down on its own when set on high.

I also just checked the temperature coming from the vent after running the AC on LO temp for about 10 minutes. It was reading 50 degrees with a digital meat thermometer and 46 degrees with an infrared thermometer. So, when the car is cool, the AC seems to be working fine.

Just wondering about the fan speed and the fact that the car gets really warm when it slows down on its own.

Any help or ideas would be most appreciated. I'm not ready to take it to a dealer, just hoping to figure it out.

 

Yes, it slows down when the fan is on full bars all the way to the right. The cabin filter is clean. The car has 180K. Thank you!

 

My mechanic was replacing the front brakes for the first time at 180K (nice!!) and I asked him what he thought it might be. He speculated that the fan motor could be starting to fail so it ends up slowing down when it has to work hard on hot days, but he also said it could be a relay, capacitor, or another problem. I am wondering why the air coming out does not seem as cold when the fan slows down. Its like the compressor is not fully working and the fan is slowing down to match the compressor. Again, I have no idea though.

 

Yes, my mechanic said he probably could only diagnose it when it is having the problem. His shop may not be the best place to diagnose this issue. I am hoping someone on this forum may have experienced this problem too or might have a pretty good idea of what it may be.

 

Thanks!!!