Blower motor does not work on high.

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.

Could be a number of thing's ! Testing the electrical circuit is the way to find out what's wrong . Using a wiring diagram and a DVOM - digital volt ohm meter . Videos on youtube showing how to test it ! Without testing i would only be guessing . Does it work in high speed ? In high speed it by-passes the resistor . If it doesn't work in any speed more then likely the blower motor is the problem !
Air Speed
The HVAC control assembly applies ground to the blower motor control circuit that corresponds to the selected blower speed. The resistors and the blower motor are in a series circuit. The following list represents the number of resistors in series with the blower motor per particular speed request:
• Low speed--3 resistors
• Medium 1 speed--2 resistors
• Medium 2 speed--1 resistor
When the operator requests High speed, the HVAC control assembly applies ground directly to the blower motor through the high blower motor control circuit. The resistor card has a fusible link which, if blown, will require that the card be replaced.

Blower Motor and Resistor Diagnostics by Wells

I agree with Dan.... The blower motor resistor is the problem

should be just above the blower motor. You will need to remove the glove box door to gain access.

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

You can replace the relay and see if it works,if not Autozone will refund the money back.Here's a link to relay.

I would say the switch

The Blower Motor Resistor is located on the passenger side firewall, not far from your A/C's H-Valve (or expansion valve), going inside of the vehicle. The blower motor resistor has a 4 or 5 way black connector plugged into it and this is the only visible portion of the Resistor you will see. Remove the wiring connector and remove the 2 or 3 screws with an 8 mm or 5/16" socket (8 mm and 5/16" are the same). Once the screws or fasteners are removed, just pull the blower motor resistor out of the firewall and if you look at it, it will have various coils of wire on it, sometimes it will show burnt coils, but you can always check the various coils with an Ohm-meter.

Aside from that, install the new Blower Motor Resistor and Voilà! Your inside Blower Motor should work just fine.

A brief note here, if your fan doesn't work when the fan switch is on High, then it's not the Blower Motor Resistor, but possibly the Blower Motor itself. Should this occur, please get back to me insofar as how to replace the blower motor and why the blower motor's wires have to be twisted...even with the new blower motor fan.

Best of Luck,

"00 Buck"

"Still living on the Right Side of Dirt..."

The switch, high blower speed relay or the wire harness at the blower motor has gone bad. The highest setting 5 has no resistor, so the blower runs on high but the high current flow ends up burning up the switch's contact on that setting or the relay and may be the resistor wire harness at the blower motor has gone bad. Common would be the switch it self, if the switch is good. Then it's going to be the blower relay or wire leads at the speed resistor by the blower motor under the glove box by the passenger leg compartment. Keep me posted, be glad to help you get your Silverado running 100% again soon.

When the blower is on speed 5, it is a direct 12 volts for high speed and the first four operate through the resistor, check your breaker for the blower motor to insure it is not cutting out.

you need to change blower motor resistor by blower motor right behind blower right side under dash.