Same issue with blower fan

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.

for the fan the motor resistor would be a possible cause, but the heat itself doesnt come up to temp? That wouldnt be a fan problem.

Hi, check fuse 12 first. If it is good, you will need to replace the blower resistor. The high speed relay is built into the resistor. The resistor is next to the blower motor and looks like the picture below. There is a connector in the resistor and the 2-wire connector coming out of the resistor attaches to the blower. The blower is usually under the dash above the passenger's feet. You may have to remove a kick panel to see the motor and resistor. Please let us know if you have any questions, and thanks for using FixYa.

The blower motor fan is controlled by the blower motor resistor.Its the resistor which controls the fan on respective speed which you select.But if the resistor goes faulty,then it will not be able to set the required speed which you set for fan,so it works on high speed only. In this case you will have to replace the blower motor resistor. Check fog for the location of blower motor resistor location:--- see part number 8 in the diagram below.

The blower motor resistor is located next to blower motor under the dash.Its fitted with 2 screws and a wiring connector.You have to remove the screws and wiring connector and take the resistor out and place the new resistor in same position and connect the connector as well as screws. ------------------- this should help.Thanks.Helpmech.

Hi!!
It could be the Blower Motor Fuse or Relay and they should be located in the cabin Fuse Box, if both are OK, it could be the blower motor resistor, located on the blower motor housing, it is the part where the electrical connector goes into and it's got a pigtail connector that goes to the blower motor, it is attached to the blower housing by three screws. Here are some pictures for better identification.
FRONT VIEW
CONNECTOR FROM RESISTOR TO BLOWER MOTOR
SIDE VIEW

To test it, make sure the electrical connector has voltage when the FAN is on, if voltage is present, it means relay and fuse are OK, plug the connector into the resistor and check voltage on the pigtail connector, if voltage is present, the resistor is OK, voltage varies according to the speed selected. To check the blower motor, apply 12 volts and ground the the motor terminals, it should kick in in Hi speed, if not Replace Blower Motor.
A HELPFUL - 4 THUMBS - rating for this solution would be greatly appreciated. Thank you for using FixYa.

It's the switch in the control panel. Would you like instructions for replacing it?

on this model you need to inspect the blower resistor and connector,
a poor connection at the resistor and connector causes heat and burns the wiring.
if its burnt replace the resistor and find a good connector at the salvage yard.
it is near the blower motor

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

No heat or no air volume? No heat may mean no coolant! check it now! Your 4.2 wont stand for being overheated. No volume, check the fuse, if ok then turn on you fan and check for voltage at the electrical connector at the blower motor (under the glovebox). If you dont have a test light, tap the blower motor . If that kicks it to life you need a blower motor.