2003 tundra A/C and Heat fan squeels - how can i fix?

this sounds like you will have to replace the blower motor resistor board to fix the problem.

Above the passenger's feet, 3 bolts to loosen and it comes right out...

May have broken a connection/shorting in the blower resistor pack which controls motor speed. Can get fragile with older vehicles.

1st of all, you need to check your anti-freeze level. If its not full, the coolant cannot/will not flow throughout your heater core which the coolant flow through to heat your vehicle. If it is indeed up to the proper level? Than, yes I would look into the thremostat. It may not be opening up.

That's what it sounds like to me.

If the blower is making noise than the only thing you can do is replace it.

Blower resistors typically operate by dropping voltage through a set of resistors. The lower the speed the more resistance is needed. High speed requires no resistance and usually bypasses the resistor assembly.

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That means the fanbelt on the alternator is not tight enough or needs to be changed, if the belt on powersteering goes via A/C than it might be too tight on the powersteering pulley.

Well it sounds like the blower motor relay is out you might also need a blower motor if it is using to much juice on high speed then the blower motor is probabley about to go out and with the noise you are describing it sounds like a bearing in the blower motor is about to go out so probabley should change the blower motor and the blower motor relay.

Run 12V directly to the motor and see if it will run, if it dosent than the motor is bad, if it does than the resister is bad, the resister makes the blower run and also regulates the speeds for the blower, but chanses are if it was making a high pitch squeel before it quit the motor went out.

Sounds like something in the blower motor fan (also called the squirrel cage) Sometimes mice bring things into this for a nest.