4 speed blower (fan)

The blower motor relay is energized when the Blower Motor Control is set to the High position. This removes the blower motor resistors from the circuit and battery voltage is then applied directly from the HVAC BLO fuse (RH IP Accessory Wiring Junction Block) to the blower motor though the relay switch contacts. The blower motor then runs at high speed.

HVAC Blower Controls Circuit Description
The blower motor is a variable speed motor. The motor operates at a higher rate when voltage is increased to the maximum level.
The blower motor resistors reduce the voltage supplied from the A/C FAN fuse (LH IP Accessory Wiring Junction Block) when the blower control is set at low and medium speeds (speeds 1-4). The blower motor relay is energized when the Blower Motor Control is set to the High position. This removes the blower motor resistors from the circuit and battery voltage is then applied directly from the HVAC BLO fuse (RH IP Accessory Wiring Junction Block) to the blower motor though the relay switch contacts. The blower motor then runs at high speed.

I looked at 05 avalanche 1500--automatic hvac. The blower fuse is hot all the time. The fuse has an input leg and output leg, even if the fuse is blown, the input leg would still have voltage. If no voltage, you could use jumper wire connected to voltage on the output side of fuse cavity to see if blower would work. If you use jumper, use an inline fuse.
Yes, it could be something wrong with fuse box or wiring circuit?

YJ car.
the blower is dead. is that it?
does it blow full speed on high
do you have 12v on terminal A of blower , term B is 0v ground
got that, then the blower is dead.
if not 12v, then the controls are bad.
http://www.jeep4x4center.com/knowledge-base/index.htm?utm_source=cj#service

page 47
4 parts to make blow
1: fuse 12 good.
2: switch heater /on off.
3: high, med,low speed, use high, its direct.
4: the blower,
one of those points has no 12v on high,
use a simple voltmeter to find the failed point.

possible faulty new resistor, could be a bad ground wire shorting out.
older chevys are good for the ground wire corroding, heating up and shorting wit the wires near it, this can cause the fan to get stuck on high.

you probably need new control switch.

There should be a high speed blower relay that bypasses the resistor for slower speeds.
Check with an auto parts store or the dealer.

Check the blower motor resistor.

You need to get the blower motor resistor replaced.This is your problem.It is located by the blower motor.There will be a connector from the blower to the resistor.The resistor controls the fan speeds when you turn the knob on the control head.The blower motor is on the passengers side under the dash.Hope this helps.Good luck.

THE BLOWER MOTOR RESISTOR FAULTY IF YOU HAVE ONLY 1 FAN SPEED ALSO AC AND HTR CONTROL SWITCH BAD.WATER LEAK UNDER GLOVE BOX COULD BE THE HEATER CORE LEAKING IF LEAKING ALL THE TIME WHEN THERE IS NO RAIN.

The problem usually stems with the blower motor resistor,high speed by-passes it and there-fore the controller is sending power but the resistor has gone open and the speeds can't be regulated.