Hello all. I had the heat cranked up in the blazer today, and after a while the it started making a squealing noise at any fan speed . (Manual controls, 04 blazer) Now the interesting thing: when I turn it to cold, and wait a bit, the noise stops. It also stops if I turn off the fans entirely.

What do you all think I should look at first? Blower motor?

 

Actually the first thing I'd check based on those symptoms is the blend door actuator. The plastic gear inside the motor can crack and not push the door to close fully when heat is selected, which causes a whistling noise.

The blend door actuator sits on top of the heater box, and the shop manuals say you have to remove the entire dash to replace it.
It is accessible from behind the glove box IF you have small agile hands and a flex head ratchet to get to the three 7mm screws that attach it to the heater box. There are a couple videos on the YouTube showing how to do this. If I can find it later I'll add the link.

 

Okay, I'll check out the blend door. Is there a way to check if it's closing without disassembly?

If I set it to heat, it doesn't start squealing right away- it took about 10 minutes of driving with heat on to start squealing.

 

Ok, I did a little more troubleshooting at home, instead of the "try to troubleshoot on the way to work" kind.

It's doing it regardless of temperature now, and squeals a lot more on the higher fan speeds. I'm going to go ahead and order a blower motor since it's a lot easier than blend doors, haha. I'll be sure to report back!

 

It might be visible from the engine bay if you remove the blower motor resistor. That sits on top of the heater box.

Good luck, and I hope that it's a simple fix for you to solve the whining noise.

 

I recently had that same issue on my 2001 Blazer, and the problem turned out to be a blower motor that was bone dry inside.

I took the blower motor out, and took it apart. There are 4 metal tabs you can pry open to take the housing off the motor.

All I did was clean the brushes, the magnet, and everything on the inside with electrical cleaner. There was lots of dried up grease on the inside. It was black. I cleaned it till there was zero grease on the inside. You don’t want grease on brush motors. And then I coated everything with Deoxit so it doesn’t corrode.

Now there is a shaft that rides on a brass bushing. The brass bushing is on the housing, and the shaft is attached to the motor and the fan blades. I put some thick silicone grease and a couple drops of silicone spray lube on the bushing, and I put every back together.

You can actually see the shaft and the brass bushing from the engine bay when you look at the front of the blower motor towards the coolant overflow tank.

It’s been about 4-5 months since I did all this, and the blower motor still works great, no noise at all. And it’s the original blower motor from 2001. Still going strong.

Or….

You can just buy a new blower motor and swap it. I just didn’t want to spend the money, and I knew it was gonna be a simple fix. Usually, if something that spins makes noise, there’s probably not enough lubrication, or the bearings are shot. There’s no ball bearings, just a brass bushing in our blower motors, and my bushings were in good condition, surprisingly.

 

Noted! I've got a spare blower motor sitting on my shelf for when the noise comes back, but it's actually been behaving recently, haha.

 

lol. Yeah, the intermittent noises are always fun to hunt down. Good luck!