How to Test a Blower Motor Resistor Pack.

Adam Mechanic

How to test the resistance or failure in a blower motor resistor pack with a multimeter. Why do they fail and what are the symptoms? Please like and follow for more content.

Transcript

00:00Hi everyone just a quick video on variable resistors, resistor packs as some people call

00:06them that you use for your blow motor fan for inside your car so where are these used these

00:12are only used on the older older type of fans where you've actually got different speed settings

00:17if you've got a new digital one that's got a a constant variable all the way around there then

00:22that'll be a variable resistor or more accurately it'll be a potentiometer because that'll have a

00:28track there and that'll give different resistance as you go around so you'll only get these resistor

00:33packs for these that have different fan speeds so how does it work well as the name suggests there's

00:41various levels of resistance within this for different speed settings so obviously zero the

00:47supply to the fan will be zero volts as you'd expect and then at speed four what you get is direct

00:56battery voltage so that would actually bypass these and you'd end up with direct 12 volt

01:01straight from the battery so at speed 4 you get 12 volts so the resistor pack is for the settings

01:08in between so that's your answer to what the symptom would be if your blower motor only works on full

01:12speed or not at all on zero then it'll be the resistor pack that's failed the resistor pack goes

01:17down all the speeds in between full speed and zero will go down so we're going to test the resistor pack

01:25because this one has failed this is the old one and i've got the new one here um roughly speaking

01:29you can obviously leave these plugged in the car and test them uh for voltage and what you'd expect

01:35at speed three is around about nine volts because the resistor's holding back three volts at speed two

01:41you'll be looking for something around six volts and at speed one it'll only be allowing three volts

01:46worth of current uh to the fan and that's why the speed of the fan changes at different speed settings

01:51because you're using resistors to restrict the amount of current and voltage uh to your fan

01:57so if i look at this brand new one here that i'm about to put in the car i'll have four pins here

02:02um and that is i'm going to be putting my red multimeter lead onto this pin and then the other three

02:07will represent the three speeds one two and three uh on the um on the on the on the dashboard there so

02:14set my multimeter to omega to ohms to resistance and i've put it on the lowest setting here which is

02:20200. i'm not expecting huge amounts of resistance there's not a lot of wiring in these uh and as you

02:26can see the black wires on com which is for earth and then i've put it on the the ohms uh omega sign

02:31there as well um one showing open circuit if i quickly cross these it should show complete circuit

02:37and give me a reason of how much resistance is lost um so i know that it's calibrated and working so

02:43first of all put it on on this one as i said i would so pop it there and then i'll move along so the first pin

02:54is dancing around a little bit let me just get that to settle down

02:58one ohm so i've got one at one ohm

03:04on pin number one on pin number two i have

03:13two point

03:16five or thereabouts 2.5 ohms

03:23got 200

03:27and then the third one will be

03:32because they're not necessarily in order so i'm doing this test so i can show which speed settings which

03:36excuse me

03:50got a lot of movement here

03:51point four ohms or thereabouts so 0.4 ohms at 200. so look at it this one here is giving the least

04:09resistance so that will be speed four the middle one's giving the highest resistance so that will be

04:14speed one and then the first one that i touched is showing one ohms of resistance that will be speed

04:19two the more resistance the less current and voltage is allowed through the slower the motor will go

04:24just so you know if yours has failed the quick test to look at it is i'll do it on this one as well so

04:29you can see the difference so as i say when these packs go down they all go down so if i put my

04:35red one there again and touch any other pin i touch all three of them

04:42still showing open circuit one represents open circuit open circuit there open circuit there and

04:48open circuit there so all these packs collapsed and therefore the customer would only have their

04:54fan block where working on on 12 volts on the highest speed setting for the fan only

04:59um so yeah why do they fail well obviously they live in the dashboard so they get pick up moisture

05:06and sometimes like this one is hopefully you can see a little bit of corrosion on there so that can be

05:10a reason corrosion obviously is going to take more current to push through to do its job so the current

05:15is going to build up and that could blow a resistor such as this one here but also there might be

05:20another reason a common one this was um normally the blow motor so that's your blow motor itself

05:27if it's sat in the dashboard for 10 or 12 years or so uh maybe even less and it builds up resistance

05:32in the motor the motor can degrade also the bearings and the output shaft can get rust on them and bits

05:38of moisture and it doesn't run smoothly so it takes more effort for that motor to be turned and spun

05:43and therefore it needs more current so the current coming in through this resistor pack will be higher than

05:47what it was designed for so you can take this out and replace it but a lot of customers will find

05:52that within two or three weeks it's blown the brand new one because this isn't the cause this is the

05:58consequence of normally your blow motor uh wearing out generating more resistance and therefore

06:03blowing your resistor pack um i hope that makes sense and uh we'll see you on the next one

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