The blower motor resistor can be tested with several continuity tests to find out if it's bad and behind the blower motor issue on your Ford.
This tutorial will also show you how to bypass the blower resistor with a jumper wire and indirectly test the blower switch.
Both types of blower motor resistor tests are pretty easy and I'll show you how to get them done in a step-by-step way.
As a cross reference: If your Ford vehicle uses one of the following blower motor resistor numbers, this tutorial applies to it:
- Airtex/Wells 4P1367.
- Dorman 973014 and 973015.
- Duralast JA1505.
- Motorcraft YH1699.
- Standard Motor Products RU445.
Contents of this tutorial:
The following tutorials on testing the blower motor and blower switch may come in handy:
- How To Test The Blower Motor (Ford 4.6L, 5.4L).
- How To Test The Blower Motor Switch (Ford 4.6L, 5.4L).
Basics Of Troubleshooting The Blower Control Resistor
The Ford blower motor resistor assembly, covered by this tutorial, has 3 different resistors in series and depending through which resistors the blower motor current is flowing thru' (on its way to ground) you'll get one of three speeds: LO, M1, and M2.
To be more specific, these resistors reduce the amount of current flowing thru' the blower motor (and thus reducing its speed).
The one blower motor speed that doesn't depend on the blower motor resistor assembly is HI since the blower motor switch accomplishes this speed by completely bypassing the blower motor resistor assembly.
This reduction in the blower motor's current is the end result of the resistor converting this electrical energy into heat energy and boy does the resistor assembly get hot! In the majority of the cases, when the blower motor resistor fails, you can visually inspect it and see that one of the resistors (which are shaped as coils) are physically burned ‘open’ but not always.
The cool thing is that you can check the integrity of each resistor and the state of the thermal fuse with a multimeter and that's how I'll show you how to test it in this tutorial.
|Blower Resistor Circuit Descriptions|
|1||LT GRN/WHT||M1 Speed Input From Blower Switch.|
|2||ORG/BLK||Input From Blower Motor.|
|3||BLK||Output to Chassis Ground.|
|4||YEL/RED||M2 Speed Input From Blower Switch.|
NOTE: If the color of the wires described above DOES NOT match what's on your particular vehicle, don't worry. The circuit descriptions are the same for all of the Ford vehicles covered by this repair tutorial (see the ‘Applies To:’ box on the right column).
Where To Buy The Blower Resistor And Save
Ford's blower motor resistor connectors usually are found melted. If this is the case in your case, you'll need to replace the connector. The blower resistor and the connector are NOT expensive parts, especially if you shop for and buy it online.
The following links will help you comparison shop for the Ford Motorcraft blower motor resistor and the resistor connector:
Not sure if the above blower motor resistor fits your particular Ford? Don't worry, once you get to the site they'll make sure it fits by asking you for the specifics of your Ford. If it doesn't fit, they'll find you the right one.
TEST 1: Checking Continuity Of The Blower Resistor
The first thing we'll do, to find out if the blower motor resistor is bad (or not) is to check the continuity between certain pins of the blower resistor.
In the test instructions below, I'll tell you which ones you'll be testing. The illustrations in the image viewer will help you in further identifying the pins that should have continuity.
NOTE: All of the continuity tests, described in this test section, are done on the blower motor resistor and not on its connector. The illustration in the image viewer identify the male spade terminals on the blower resistor.
OK, let's get this show on the road:
Disconnect the blower motor resistor from its electrical connector and remove it from its location. Set your multimeter to Ohms mode (Ω).
Don't have a multimeter or need to upgrade yours? Check out my recommendation: Buying A Digital Multimeter For Automotive Diagnostic Testing (found at: easyautodiagnostics.com).
Visually inspect the condition of the blower resistor's coils and it's electrical connector.
Is the connector melted? Are the coils in one piece?
Probe terminals 2 and 3 with your multimeter test leads to check the LO speed circuit (see image 1 of 4 in the image viewer).
Your multimeter should register continuity. You'll probably see a resistance of about 7.1 Ohms ( Ω).
NOTE: See image 4 of 4 to identify the proper male spade terminals to probe).
Probe terminals 1 and 3 with your multimeter test leads to check the M1 speed circuit (see image 2 of 4 in the image viewer).
Your multimeter should register continuity. You'll probably see a resistance of about 3.3 Ohms ( Ω).
Probe terminals 4 and 3 with your multimeter test leads to check the M2 speed circuit (see image 3 of 4 in the image viewer).
Your multimeter should register continuity. You'll probably see a resistance of about 0.6 Ohms ( Ω).
This test also test the continuity of the blower resistor thermal fuse.
IMPORTANT: There's a good chance that you won't see exactly the resistance values I've listed (on your multimeter). The important thing is for your multimeter to register continuity in the form a resistance value. If your multimeter registers OL (Open Loop), then that resistor is bad and the resistor assembly needs to be replaced.
Let's take a look at what your test results mean:
CASE 1: One or more of the resistors you checked with the multimeter DID NOT have continuity. Repeat the tests just to make sure of your test results.
If continuity is not present where indicated in the test steps above then this confirms that the blower motor resistor is bad and needs to be replaced.
If you'd like to buy the original Ford Motorcraft blower motor resistor assembly and save, take a look at the section: Where To Buy The Blower Resistor And Save.
CASE 2: All circuits tested had continuity where indicated in the test steps. This is good and is the correct and expected test result that tells you that the blower motor resistor is OK and not the cause of the blower motor speed problem.
You can stope here if your blower motor resistor passed all of the continuity tests in this test section. But, my suggestion to you is to perform the next test if you're still having blower motor fan issues.
The next step indirectly tests the blower switch on the A/C Heater control panel by bypassing the blower resistor with a jumper wire: TEST 2: Using A Jumper Wire To Bypass The Blower Resistor.