Do i have a bad HVAC Fan Switch?

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.

Tell us what make an model of vehicle you are using in your description of the problem. Blower not working can be caused by:
1. Blown fuse
2. Bad fan switch
3. Bad resistor speed selector unit (changes voltage going to fan motor.
4. Melted or bad connector, usually between switch and motor.
5. You have lost the ground from the fan going back to the battery. ie, a bad connection.
You will need a volt/ohm meter after you check the fuse.
Make sure you have battery voltage (about 12 volts) coming to the fan switch. If you do get 12 volts, follow it in the circuit going to the blower fan until you stop getting 12 volts. Where it stops is where the problem is. You can also start the test right at the blower fan with a meter to see if the fan is getting 12 volts and work backwards towards the switch.
Most likely cause: Bad resistor pack or connectors melted going to it, followed by a bad fan switch.
Good luck!

Check for voltage and ground at the fan connector, with hvac turned on. If good voltage and ground with no fan action, suspect the fan. Use a testlite. Did you check for voltage at the applicable fuse circuit? Even if the fuse is good, if no voltage, the circuit is still dead.

Do you know how to use a volt meter ? Need to check for voltage at the motor ! , need a wiring diagram. Most of the time other people on here will tell you to check the fuse's , that doesn't end up being the cause ! Most of the time it's the motor or a wiring problem ! I have seen the wire in side the rubber boot ,when you open the rear hatch break causing a no power situation to the motor . If you open the rear hatch ,door ,lift gate , what ever you call it . If you look when it is open there is a rubber boot connecting the body to the door , there are wires in side . There have been known to break ! This next part is a FORD pinpoint test. This is how ford says how to check !
PINPOINT TEST B: THE WIPERS ARE INOPERATIVE - REAR WINDOW Test Step Result / Action to Take B1 CHECK CIRCUITS CBP43 (GY) AND SBP19 (BU/RD) FOR VOLTAGE

• Key in OFF position.
• Disconnect: Rear Wiper Motor C476.
• Key in ON position.
• Measure the voltage between rear wiper motor C476-3, circuit CBP43 (GY), harness side and ground; and between rear wiper motor C476-4, circuit SBP19 (BU/RD), harness side and ground.
  >
• Are the voltages greater than 10 volts?

Yes
GO to B2 .

No
VERIFY SJB fuse 43 (5A) and fuse 19 (25A) are OK. If OK, REPAIR the circuit(s) in question. TEST the system for normal operation. B2 CHECK CIRCUIT GD150 (BK/WH) FOR OPEN

• Key in OFF position.
• Measure the resistance between rear wiper C476-1, circuit GD150 (BK/WH), harness side and ground.
  >
• Is the resistance less than 5 ohms?

Yes
GO to B3 .

No
REPAIR the circuit(s) in question. TEST the system for normal operation. B3 CHECK THE MULTI-FUNCTION SWITCH

• Key in OFF position.
• Disconnect: Multi-function Switch C202.
• Carry out the multi-function switch component test. Refer to Wiring Diagrams Cell 149 for schematic and connector information.
  
• Did the multi-function switch pass the component test?

Yes
GO to B4 .

No
INSTALL a new multi-function switch. REFER to Section 211-05 .

id find blower motor and hit it with a hammer if it turn on its bad also look at the wire to the resistor they melt down if its bad put new connector and resistor in iv done a few

Have you replaced the fan switch? Or if you have a voltage meter you can check for voltage at the motor, and at the switch then in between where you can to isolate the short if there is one. Also since you mention running a separate 12 positive wire into the controls be sure that you connected it correctly. Also check and see if you have voltage at the wire you added. If you have voltage at the wire you added, then you need to check if the switch is letting power through it. So use your volt meter to test for voltage, check all the fan speeds also. I'm guessing you had problems with this before and that is why you have ran your own wire. So you probably kept blowing the fan fuse, this would most likely be from a bad switch, a short, or a bare wire.

I would check all fuses associated with the HVAC, if all fuses are good and you are sure the new part you bought is good then the problem would be in the control unit.

{: ) Regardless of the blower motor switch position, recirculation is available only in the panel and bi-level mode switch positions. Including the OFF position. The mode switch must be placed in either the panel or bi-level position before the blower motor switch is placed in the OFF position. In order to reduce windshield fogging, outside air is circulated when the mode switch is in the defrost or defog positions. If the recirculation switch is pressed into the ON position when the mode switch is in an unavailable mode position, then the recirculation switch LED will flash 3 times. If the HVAC control module detects a fault with the recirc door the HVAC control module will try to drive the actuator for a predetermined amount of time, to outside air, which is the defaulted position for the recirculation actuator.
As for your blower not full force at level 5, check first the BLWR fuse 40A at the underhood fuse block. If its okay, most likely you have a malfunctioning blower motor resistor assembly.

Hello,

I have a 2003 Chevy Cavalier. The HVAC airflow dial only works on high setting. We checked the fuse and it's o.k.

What now?  Any estimate as to repair cost? 

Thank you

CHECK THE HVAC CTRL FUSE.

WITH A TEST LIGHT CHECK THE BLOWER RESISTOR FOR POWER ON THE YELLOW, TAN, PURPLE, AND LIGHT BLUE WIRES. THE ORANGE WIRES CONTROL THE HIGH SPEED CIRCUIT. DO THIS FOR EACH POSITION OF THE BLOWER SWITCH.

THE BROWN WIRE ON THE HVAC CONTROL CONNECTOR 1 POSITION B COMES FROM THE HVAC FUSE 20 AMP. NO POWER ON THAT WIRE WILL CAUSE THE BLOWER TO NOT FUNCTION ON THE LOWER SPEEDS.