Heater Motor Question - Impala Tech
Electrical & Wiring Troubleshooting electrical problems

 
LinkBack Thread Tools
post #1 of 4 (permalink) Old 12-18-2016, 09:13 PM Thread Starter
Member
 
Join Date: Jul 2016
Posts: 84
 
Heater Motor Question

I don't quite understand the relationship between the resistor and the fan motor. It appears the motor is on high when the resistor is bypassed, medium and low through the resistor. Assuming that's true, how can I determine if the motor is at fault or the resistor is at fault (seems to run on low speed only). Possibly wire the motor directly to the battery and see what happens?? Or could the switch be at fault?? I do see a faint spark when moving the switch between positions but that may be normal. This is a '62 without A/C (blower motor has a single wire to it).
rbwinston is offline  
Sponsored Links
Advertisement
 
post #2 of 4 (permalink) Old 12-18-2016, 11:30 PM
Moderator
 
Join Date: Jan 2006
Posts: 12,362
 
A DC motor (all DC motors from fans to toy trains) rotate faster as the voltage increases, or slower as it decreases. They also rotate backwards if you reverse the polarity (+ with the -, and the - for the +).

Now you can reduce line voltage by adding resistance to the circuit. In the case of a toy train or your gas gauge sending unit it utilizes a rheostat (some ni-chrome wire wrapped around an insulating form that has a contact point that sweeps across the windings to vary the voltage). In the case of the toy train it controls the speed of the locomotive by varying the voltage to the DC motor. In your gas gauge the float moves the rheostat arm depending upon the gas level that reduces the amount of voltage that goes to ground. As the resistance increases to 60 Ohms (more windings) the voltage to ground drops and the gauge reads empty. At the full nominal voltage of 12 Volts to ground (few windings in the circuit it reads full. If you have a bad ground (with a lot more resistance than 60 Ohms) then it will always just sit ther at empty and laugh at you!

DC circuits are extremely easy to understand if you understand the function of resistors, batteries and the concept of a switch or load. In fact it is as easy as PIE (the letters used to express Ohm's Law) that is used to calculate values to predict what the reading should be ahead of time. Or allow you to correct or tune a circuit to make it behave as expected (say you are trying to use a 12 volt battery in an older than a 1955 Chevy that used a six volt battery for everything). Plug in a 12 volt battery in a six volt car and your volt gauge and your gas gauge go up in smoke though your head lights are much brighter till they also burn up.

From your description of the problem you have either a bad switch or a blown (burned open) resister. My money is on the switch being bad as it isn't feeding any power on high speed. My guess is the contact points in the switch have burned away and are not making contact to complete the circuit.

Big Dave
Big Dave is online now  
post #3 of 4 (permalink) Old 12-23-2016, 07:10 AM Thread Starter
Member
 
Join Date: Jul 2016
Posts: 84
 
Quote:
Originally Posted by Big Dave View Post
A DC motor (all DC motors from fans to toy trains) rotate faster as the voltage increases, or slower as it decreases. They also rotate backwards if you reverse the polarity (+ with the -, and the - for the +).

Now you can reduce line voltage by adding resistance to the circuit. In the case of a toy train or your gas gauge sending unit it utilizes a rheostat (some ni-chrome wire wrapped around an insulating form that has a contact point that sweeps across the windings to vary the voltage). In the case of the toy train it controls the speed of the locomotive by varying the voltage to the DC motor. In your gas gauge the float moves the rheostat arm depending upon the gas level that reduces the amount of voltage that goes to ground. As the resistance increases to 60 Ohms (more windings) the voltage to ground drops and the gauge reads empty. At the full nominal voltage of 12 Volts to ground (few windings in the circuit it reads full. If you have a bad ground (with a lot more resistance than 60 Ohms) then it will always just sit ther at empty and laugh at you!

DC circuits are extremely easy to understand if you understand the function of resistors, batteries and the concept of a switch or load. In fact it is as easy as PIE (the letters used to express Ohm's Law) that is used to calculate values to predict what the reading should be ahead of time. Or allow you to correct or tune a circuit to make it behave as expected (say you are trying to use a 12 volt battery in an older than a 1955 Chevy that used a six volt battery for everything). Plug in a 12 volt battery in a six volt car and your volt gauge and your gas gauge go up in smoke though your head lights are much brighter till they also burn up.

From your description of the problem you have either a bad switch or a blown (burned open) resister. My money is on the switch being bad as it isn't feeding any power on high speed. My guess is the contact points in the switch have burned away and are not making contact to complete the circuit.

Big Dave

Sounds more than reasonable. I'll start there. Thanks!
rbwinston is offline  
 
post #4 of 4 (permalink) Old 12-24-2016, 12:51 AM
Senior Member
 
Join Date: Apr 2013
Location: Canada
Posts: 324
 
Quote

At the full nominal voltage of 12 Volts to ground (few windings in the circuit it reads full. If you have a bad ground (with a lot more resistance than 60 Ohms) then it will always just sit there at empty and laugh at you!

__________________________________________________ __________________________________________________ __________________________________________________ __________


For those who read this, I think Dave meant to say " If you have a bad ground (with a lot more resistance than 60 Ohms) then it will always just sit there at full and laugh at you!

A 60's GM with a bad ground on the fuel gauge will show way past full.
Darth is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Impala Tech forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome