Chevy and GMC Duramax Diesel Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
1,044 Posts
Discussion Starter #1
Replaced the resistor next to the blower fan under the passenger side dash a couple of years ago. Went out again about a yr ago, autozone warrantied it no big deal. Just went out again and autozoned warrantied it again a couple of weeks ago. But now it decides to quit blowing again today? Any ideas? Its free to keep throwing the part at it but annoying


Sent from my iPhone using Tapatalk
 

·
Premium Member
Joined
·
574 Posts
Did you ever replace the fan or fan witch? something is drawing a higher load than normal, I would use a meter to check load
 

·
Registered
Joined
·
1,044 Posts
Discussion Starter #3 (Edited)
Did you ever replace the fan or fan witch? something is drawing a higher load than normal, I would use a meter to check load


Im not familiar with a fan witch could you elaborate on what it is and where it is? Check load going to the resistor you mean? I tested the fan the first time i replaced the resistor and that was fine. Also it worked perfectly for a few days after i replaced the resistor this time so i would doubt that it is the actual fan


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
1,044 Posts
Discussion Starter #4
Im about to test voltage how much should it be drawing?


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
1,548 Posts
I think about 8 amps or so. Look at the fuse that protects that circuit and make sure your motor is 50% or less than the fuse.



You will be checking AMPS, not VOLTS. Most DVOM testers will only be able to test 10 AMPS before blowing the tester fuse, so be careful.
 

·
Registered
Joined
·
4,933 Posts
if the winding in the blower motor have a short, it will lower the resistance of the motor and increase the current through it (and the resistors). Im not sure what the factory spec is for the resistance of the motor. The current draw of the motor will be the running voltage of the truck (14.4V) / the resistance in ohms of the motor. so a 1 ohm load will draw 14.4 amps, a 2 ohm load will draw 7.2 amps and so on. If the motor winding is low enough for the current to approach the fuses rating the motor is probably bad.

Alternately, a very dirty squirrel cage will drastically increase the load on the motor, and that will increase the current through the motor, so a cleaning of the squirrel cage may also fix your issue. Personally given how easy it is to pull out, i would start with a cleaning and then you can meter it while its out.
 

·
Registered
Joined
·
4,933 Posts
I think about 8 amps or so. Look at the fuse that protects that circuit and make sure your motor is 50% or less than the fuse.



You will be checking AMPS, not VOLTS. Most DVOM testers will only be able to test 10 AMPS before blowing the tester fuse, so be careful.
to add to that, its usually a fast blow fuse thats not cheap, so personally id measure the resistance and calculate the current as its safer for the meter.
 

·
Registered
Joined
·
1,044 Posts
Discussion Starter #8
if the winding in the blower motor have a short, it will lower the resistance of the motor and increase the current through it (and the resistors). Im not sure what the factory spec is for the resistance of the motor. The current draw of the motor will be the running voltage of the truck (14.4V) / the resistance in ohms of the motor. so a 1 ohm load will draw 14.4 amps, a 2 ohm load will draw 7.2 amps and so on. If the motor winding is low enough for the current to approach the fuses rating the motor is probably bad.



Alternately, a very dirty squirrel cage will drastically increase the load on the motor, and that will increase the current through the motor, so a cleaning of the squirrel cage may also fix your issue. Personally given how easy it is to pull out, i would start with a cleaning and then you can meter it while its out.


What do you mean by squirrel cage?


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
1,044 Posts
Discussion Starter #9
I think about 8 amps or so. Look at the fuse that protects that circuit and make sure your motor is 50% or less than the fuse.



You will be checking AMPS, not VOLTS. Most DVOM testers will only be able to test 10 AMPS before blowing the tester fuse, so be careful.


Just to be clear im testing it at the fuse box correct? Or does it not matter


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
895 Posts
To test for amps. You either need an in-line amp meter to hook into wire or a clamp on type that just clamps onto one wire. I bought a clamp on type years ago to chase down a parasitic draw.

The other thing I found was on a 2010 canyon. There is a grounding block under the hood that a bunch of circuits use to ground with. It was ok however and the trouble was in the wiring harness just upstream of the motor in the dash. The connector was burnt there and was shorting when it bounced around intermittently. I just bypassed the plug with a splice and it's been good since.
 

·
Registered
Joined
·
4,933 Posts
What do you mean by squirrel cage?


Sent from my iPhone using Tapatalk
im not sure if this pictures from our truck, i think its actually or a ram, but its close enough. i just pulled a quick image off google. This is a blower motor, it consists of the motor at the bottom, which is connected to the squirrel cage on top. That is the part that spins to move air through the system. It gets layers of dust, and can pick up leaves and even animal nests over time so it can get pretty loaded up. Taking it out and cleaning it will reduce the load on the motor, which will use less current and may extend the life of the resistors if the cage is very dirty.









Just to be clear im testing it at the fuse box correct? Or does it not matter


Sent from my iPhone using Tapatalk


the way i would do this would be to disconnect the electrical connector for the blower motor under the dash, and meter the power and ground supply to the motor with a meter for ohms. 14.4 / whatever your meter says gives you the current draw of the motor at full power.

You could do a inline current test at the fuse box, but you would likely get additional circuits on the reading besides JUST the blower motor, since the fuse likely supplies more then 1 circuit.


If you really want to test for amps without doing math, you should use one of these. They are not super accurate at low current values but it should be within 5% or so which is fine for what your trying to do. You just open the clamp, put it around the wire and it measures the current via induction. This is not as accurate as an inline read, but also doesn't pass the full current though the meter, so it can read much higher currents then a standard meter.

This is commonly called an "amp clamp" were you to want to look it up online.

 

·
Registered
Joined
·
1,044 Posts
Discussion Starter #12
im not sure if this pictures from our truck, i think its actually or a ram, but its close enough. i just pulled a quick image off google. This is a blower motor, it consists of the motor at the bottom, which is connected to the squirrel cage on top. That is the part that spins to move air through the system. It gets layers of dust, and can pick up leaves and even animal nests over time so it can get pretty loaded up. Taking it out and cleaning it will reduce the load on the motor, which will use less current and may extend the life of the resistors if the cage is very dirty.













the way i would do this would be to disconnect the electrical connector for the blower motor under the dash, and meter the power and ground supply to the motor with a meter for ohms. 14.4 / whatever your meter says gives you the current draw of the motor at full power.

You could do a inline current test at the fuse box, but you would likely get additional circuits on the reading besides JUST the blower motor, since the fuse likely supplies more then 1 circuit.


If you really want to test for amps without doing math, you should use one of these. They are not super accurate at low current values but it should be within 5% or so which is fine for what your trying to do. You just open the clamp, put it around the wire and it measures the current via induction. This is not as accurate as an inline read, but also doesn't pass the full current though the meter, so it can read much higher currents then a standard meter.

This is commonly called an "amp clamp" were you to want to look it up online.



Ok thank you for clarifying i did have the blower motor out a yr or two ago and it was very clean inside. Ill take it out and check it again first though. I believe my dad has an “amp clamp” like you were talking about because he is an ex-electrician so i will talk to him about borrowing it.
If the blower motor turns out to be toast does that mean it will need another resistor as well since it will be “blown”?


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
1,044 Posts
Discussion Starter #13
Sorry if these are basic questions but i am mechanically inclined but electrically dumb


Sent from my iPhone using Tapatalk
 

·
LHN...We ARE the Joneses
Joined
·
26,320 Posts

·
Registered
Joined
·
1,044 Posts
Discussion Starter #15
Blower motor was clean when i took it out just now so that eliminates that possibility


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
4,933 Posts
Ok thank you for clarifying i did have the blower motor out a yr or two ago and it was very clean inside. Ill take it out and check it again first though. I believe my dad has an “amp clamp” like you were talking about because he is an ex-electrician so i will talk to him about borrowing it.
If the blower motor turns out to be toast does that mean it will need another resistor as well since it will be “blown”?


Sent from my iPhone using Tapatalk
depends, if the resistor pack is shot now, then yes, you will need to replace it either way, but i would not replace it until you find out why it keeps blowing. My guess is the motor is shot as that is the most likely way the circuit would exceed current rating without blowing fuses, but without being hands on its hard to tell you what it is or is not, just what it could be.

If you dad was an electrician there is a very high chance he has an amp clamp.

Edit: To clarify, an electric motor for those who may not know uses a ton of very thin wire with a very thin enamel insulation wrapped up tighly into coils. So normally, current would have to flow through the entire winding. This creates higher magnetic flux for a stronger motor, but it also reduces the current drawn by the coil, as the longer the wire is, the more resistance the winding has, and the less current can flow through it.

If you were to have a section of the coil rub through the enamel insulation, it could short a section of the coil which would bypass that length of wire. This would reduce the power of the motor, but more importantly would increase the current through the coil, possibly significantly depending on where the failure is in the winding.

Since its not a dead short, the fuse does not blow, but the current draw goes up which means the resistor pack has to dissipate more heat then it is designed for which results in failure of the resistor elements.

Were you to pull the motor apart to the windings you could verify this but its not really worth it, you should be able to meter the pigtail off the motor for resistance and get basically the same result, you may want to turn the cage to several points so that you get readings across each coil.



This is a cross section of a generic brushed motor.

B points to the brushes, A points to the commutator bars and C is the windings previously mentioned. The D winding are replaced by magnets so dont worry about them. when the motor turns, 2 of the bars on the commutator touch the brushes, this connects certain coils to spin the motor, when the motor turns, different cars connect to the brushes and connect different windings to spin the motor and so on until you remove power. You may have several good windings, so if you dont meter the motor through its whole range of motion you may not test the bad winding if one exits because the 2 power wires into the motor (+ and -) go to the brushes.
 
1 - 16 of 16 Posts
Top