96 K1500. High setting on blower motor not working. Every other setting working, new blower motor. I suspect this is the high speed relay under the dash, or wiring, or blower switch on the dash.



Any thoughts?

 

Welcome from Florida. Don't forget to check the blower resistor.

 

Because of the heavy current required for the blower motor to work ,to prevent early destruction of switch contacts, a hi speed relay is used to accomplish this .
That relay is usually located on the firewall in the engine compartment, but can be anywhere in the engine compartment including in the power distribution panel or fuse /relay panel.under the rear seat.

 

I think you're right about the relay being the likely problem. I think it's accessible behind the glove box. Any idea about how to test this?

 

Swap it with a different relay.

 

Any idea which ones will swap in to test?

 

Whatever one is next to it, horn, fuel pump etc.

 

I second the blower motor resistor. Common failure point when some of the speeds are inop.

 

All speeds work, except for high speed, which doesn't flow thru the resistor. This leads me to look at other suspects

 

The relay is working. I tested it on the bench, and the contacts closed properly when voltage was applied across the control side. This was confirmed when I installed it and turned on the fan, all speeds worked, but when I turned it to high, the relay clicked and nothing happened. This means the switch in the dash is good, since the switch supplies voltage to the control side of the relay when the switch is on the "high"setting.

This leads me to believe there is a short or break in the red wire from the underhood fuse panel to the relay.

Anyone have knowledge on the path of this red wire? Or maybe it's easier to run a new wire from the fuse panel to the relay?