How to Test a Blower Motor Resistor ?


Blower resistors, being a mechanical component, are inclined to wear and are the foremost common point of disappointment in a car’s warming framework. 

Blower resistors are resistors which are utilized to control the fan speed of car blowers. The fan speed can be changed either by exchanging the blower resistor resistance mechanically, employing a pivoting lever, or electronically by air conditioning framework.  

The change in resistance at that point limits the current through the engine, which directs the speed at which the blower fan works. Blower resistors, being a mechanical component, are inclined to wear and are the foremost common point of disappointment in a car’s warming framework.  

This blog will focus on mechanical blower resistors, their development and troubleshooting.  


A blower fan is associated to the negative battery terminal (too called ground) on one conclusion and to the positive battery terminal through a blower resistor on the other conclusion. The blower resistor is associated in arrangement with the blower fan. This implies that the current running through the blower engine and in this way is speed is controlled by the resistor esteem.  

 blower resistor

The client chooses a reasonable fan speed by employing a selector to put through one of the resistors within the blower resistor pack. Blower resistors are made of a few resistors with distinctive resistances. There are also two extra circuits utilized for the off state and the most noteworthy fan speed state.  

Within the off state, the blower engine is disengaged from the control supply. Within the most elevated speed state, the blower resistor is bypassed totally and the fan is associated specifically to the car’s battery, which permits greatest current through the engine.  

How to test blower motor resistor? 

When a blower resistor is defective, the fan will more often than not work at one speed as it were, ordinarily the most elevated speed setting conceivable. In some cases, as it were a few of the speed settings will be defective whereas others might work. 

Identifying the fault 

When attempting to analyze a blower fan engine, the taking after steps ought to be followed: If a car’s blower engine doesn’t work at all, there are a few components to be checked within the system: Check the combine for power on both closes employing a multimeter. 

blower fan engine

By chance that there’s control on one conclusion of the blower fan combine but not the other, at that point fuse should be replaced. Check the fan hand-off, on the off chance that the car is prepared with one. Such transfers can be tried by putting a finger on them and exchanging the fan’s control on and off. Clicking from the hand-off is a sign that the relay is working correctly. 

Check the fan itself for control nearness by turning on the fan control and checking the fan itself for +12V at its terminals. To do this, switch your multimeter to voltage measuring mode and confirm that the voltage distinction between the fan’s terminals is 12V. In case there’s no control show at the fan, suspect a wiring blame.  

In this case, it’s best to require the car to a certified auto circuit repairman. In the event that control is show on the fan’s terminals and the fan isn’t working, the blower fan is defective. If the fan works at a few speed settings, but doesn’t work at a few other speed settings, this implies that the blower resistor is defective and ought to be replaced: Find the blower resistor and segregate it from the rest of the circuit. A few common areas are close the blower fan engine, beneath or behind the dashboard, around the traveller foot well etc. 

 blower fan engine

Once the resistor is found and withdrawn, it is regularly conceivable to say whether the resistor has burned out or not judging by the physical appearance as it were. A burned out resistor ought to be supplanted by the suitable substitution from your car manufacturer. 

 If the appearance is ordinary, it is essential to degree the resistance over each person resistor. The resistors are all associated to a common point.  

Switch the multi-meter to the resistance measuring mode, join one test of the multi-meter to the common point and utilize the other test to degree resistances at other focuses. In case any of these resistances appear an open circuit; at that point the blower resistor ought to be supplanted. 

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