Heater blower motor doesn't run

Based on the detailed information you've provided, it seems that you've done a thorough job of testing the major components related to the blower motor system in your 1999 Chevy Tahoe.
Here are a few possibilities and additional steps to consider:

High Resistance in the Circuit: Even though the wiring and connectors appear to be in good condition, there might be high resistance somewhere in the circuit that only becomes significant under load. This could be due to a partially broken wire, a corroded connector, or a faulty switch. Carefully inspect the wiring harness for any signs of damage, wear, or heat exposure.

Issue with the Control Switch or HVAC Control Unit: The problem might be with the control switch or the HVAC control unit in the dashboard. These components can sometimes develop internal faults that are not immediately apparent. Consider testing the switch and control unit if possible.

Ground Connection Problem: A poor ground connection can cause voltage drop issues. Make sure the ground connections related to the blower motor circuit are clean, tight, and free of corrosion. This includes not just the ground for the blower motor, but any related grounds in the HVAC system.

Voltage Drop Test: Perform a voltage drop test on the blower motor circuit. This test is done by measuring the voltage across different parts of the circuit while the circuit is under load. A significant voltage drop across any specific part of the circuit would indicate where the resistance problem lies.

Check for Overloading or Short Circuits: There could be an issue elsewhere in the electrical system that's causing an overload or short circuit when the blower motor is connected. This might be difficult to diagnose without specialized equipment.

blower , heater dead.?
use a voltmeter, and find out what is wrong, in minutes.
first check voltage to the blower,
on fan high.
got voltage there. then the blower is bad.
no voltage there, then its not the blower bad. its controls or power feed.
my guess is you dont know that fuses that look good can in fact be bad.?>
old post. but here goes.
of lost, use a schematic, they tell you how the circuit works.
click here
on TJ
then heater........
FSM
http://www.jeep4x4center.com/knowledge-base/index.htm?utm_source=cj#service

shows 7 things can be wrong. (omg what to do, use a meter)

now click A/C heater page.
same FSM.
got 12vdc to both JB fuse 8 and PDC fuse , keyon,
both sides of fuse must be 12vdc or the fuse is BAD.
got 12vdc to blower relay pin 1, (bad relay if not, or?)
if you have 12vdc on pin1 then then check voltage at
blower B wire,
if wires is at 12vdc that means the blower switch is bad.
if the wire to the switch C3 pin C is 12vdc that means the ground to the heater control is open. correct that
if the pin C3pin C is 0v, that is good, if switch is on high
and the C1 pin A is 12v, that means the switch is bad, or wires to it cut
or the connectors to IT are corroded.

just a $10 walfart DMM meter, and bam , why is know.
no guessing or pulling out hair.
as you can see the dash heater switch grounds the blower.
if it can not ground the motor, the motor will be dead.
that is how it works.

The brown wire at the speed switch is the power wire. Powers is then directed to the blower motor resistor throught the orange, lt blue and yellows wires. The blower motor receives power through the orange wire. Check for power at the fuse with the key on. If there is no power the problem could be the ignition switch or the wiring in between the switch and the fuse block

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

According to my wiring diagram, the blue and white wire from the blower motor gets power from the key switch. The fan switch and resistor grounds the motor.
No blower fuse is listed.

Check whether you might have bad connection or contact,or e ven bad switch.

Don't know where you got your info . The heater blower motor electrical B+ power comes from Fuse F 64 a 40 amp fuse . This goes right to the blower motor on the green with orange stripe wire , The black with red stripe wire goes to the switch for high speed . There is Splice 24 that ties into the black with red stripe wire. The splice 24 turns into a black with orange stripe wire . An this wire goes to the blower motor resistor . All the switch does is route the B+ voltage through the different resistors to ground .

Thermal resistor "usually" stops working is because of faulty fan speed switch ???? Totally not true , resistor assemblies fail because of the heat associated with dropping voltage across the resistors , That is why they put the resistor assembly in the air box . Air blows over to cool the resistors . The switch is nothing more then a way to direct different speeds to ground .

Rather then listening to other people ,why not learn the right way to test electrical circuits .
Electric Testing Techniques You Need to Know

Do you know what a wiring diagram is ?
http://www.bbbind.com/free_tsb.html Enter vehicle info . Under system click on HVAC , under subsystem click on heater . Click the search button , then on the link . Use a volt meter an test , don't guess !

Either the blower motor is bad,or the blower relay is bad,check the voltage at the blower motor to see if it is getting voltage.If not,check the fan switch ,and then the relay,it is most likely the blower motor.

It sounds like the blower motor is not working. If you don't hear it running when you switch it on, check the fuse first. If the fuse is OK, you will probably need a new blower motor. It could also be a faulty fan switch or blower motor resistor. Once you remove the blower motor assembly, you can test it by putting battery voltage across the contacts with jumper wires, making sure to get correct polarity. If it does not spin, it should be replaced. If the blower does work when removed, the fan switch is probably at fault. The resistor is usually indicated when the fan works only at certain switch positions, but not all.