Electrical Heater fan out

[jeepwrecksd]

Fan is out. Just replaced it 10 mos. ago. Fuse is fine. What is the second most usual suspect besides a worn out motor?

 

[TSB8C]

Other than wiring itself (corroded/rusted connections or burned wiring), the resistor block is a common failure point. You have a resistor block that allows your fan switch to select different speeds. It is mounted in the airflow path in your plenum on the passenger side. It is easy to test or replace if needed. Just unplug the connector and then remove the two mounting screws to take the resistor out. You can visually inspect it for any burned areas or broken elements (the wire "loops" on it). Obviously replace it if any are seen. You can also measure resistance through the elements with a multi-meter. The low speed is 1.83 ohms, the medium-low is 0.87 ohms, and the medium high is 0.31 ohms, and of course there is no resistor for position 4 the high speed setting. This is also a great place to confirm other wiring by measuring voltage at this connector plug to confirm your switch and associated wires are all good. With the connector unplugged, you can measure +12V on the various pins (3 of them) when the control switch is in the different speed positions. Of course, the Chevy Blazer fan motor mod is a great way to go as well once you get the fan working again.