AC/Heater blower motor does not work on high.
 

Searched and did not find this issue. The blower motor shuts off when switched to high. Works on all other speeds. Not sure if it switch, relay, or the motor. Suddenly stopped yesterday while using AC. Changed to Bi-level to use the fan speeds, except high.

I did run a jumper from B+ to blower motor, and motor did run on high. Removed connectors from relay and resistor and reset both and no change. I will remove connectors and clean contacts tomorrow and I am planning to have the resistor tested by a co-worker that is an electronics engineer to see if it is still good. May need a new resistor or relay, not sure yet.

Re: AC/Heater blower motor does not work on high.
 

The resistors are used to drop voltage for low and medium speeds. They are bypassed when the dash switch is set to HI speed. The problem is probably the dash switch itself or the connection to it. Neither would be an uncommon problem.

Re: AC/Heater blower motor does not work on high.
 

Today removed relay, cleaned connector prongs, took apart and cleaned contacts. No difference. I was tapping on relay and fan came on high for maybe a minute then stopped. Decided to replace relay and still same problem. Also removed resistor, inspected and cleaned contacts and same problem.

Tomorrow, plan to remove climate control unit just enough to inspect unit and switch. I have inspected and lubricated temp lever when I bought truck cause lever was super hard to move. All things have been working well lately until this.

Re: AC/Heater blower motor does not work on high.
 

Figured out the problem. There is an orange 10 ga wire on motor relay that goes thru harness to firewall that has an inline fuse connected to the junction block. The fuse holder was burnt. Replaced fuse holder, now have the high speed on blower. This wire has a constant 12v.

Re: AC/Heater blower motor does not work on high.
 

Glad you found the issue. Never have seen a fuse holder on one.