My 97 f 250 blower motor only runs on high - 1997 Ford F250 SuperCab

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.

this is an indication that the blower motor resistor is bad and needs to be replaced. the system is designed to always work on high if the resistors go bad.

Here are some possible solutions. http://repairpal.com/ac-blower-inop-due-to-failed-resistor-447 Blower Motor resistor replacement Silverado Sierra Tahoe Yukon Suburban...

try resistor...

the resistor

Blower motor resistor,you need a new 1. It is close to the blower motor in the black casing.

May need a high blower relay. Under fan motor on firewall.

Run's continuously ? High speed , low , med 1,2, 3 . ????
Probably the high speed relay contact's stuck closed . The fuse for the high blower is hot at all times , low blower fuse is hot only with key on. It sparks becaused the motor turns on . If it had a short the fuse would blow . The blower motor relay is part of the resistor pack near the blower motor .

the blower motor speed control module is defective, replace it.

yes, all blower motors have them to control their speed, High, medium, low.. etc. I earn nothing by helping you, but my rating, a fixya rating and I will walk you through this