The blower motor resistor (located on top of the heater core housing and behind the glove box) isn't hard to test.
In this tutorial I'll show you how to continuity test it with a multimeter in Ohms mode (Ω).
NOTE: This tutorial only applies to the 1988 to 1993 vehicles listed in the ‘Applies To:’ box on the right column. Some 1994 Chevy/GMC pickups use this type of blower resistor.
For the 1995 and newer blower resistor test, the following tutorial will help:
To aid you in further knowing if this tutorial applies to your specific vehicle, the testing procedures apply to the following blower motor resistor numbers:
- Airtex/Wells 3A1030.
- AC Delco 1580556.
- Duralast DR791.
- Everco 20074.
- Four Seasons 20074.
- Standard Motor Products RU57.
Contents of this tutorial:
The following tutorial on testing the blower switch may come in handy:
Basics Of Troubleshooting The Blower Control Resistor
Two individual resistors make up the blower motor resistor assembly on your Chevy pickup.
As you're probably already aware, these resistors are located between the A/C-Heater control panel and the blower motor.
The purpose of these resistors is to reduce the amount of the blower motor's current that's passing through them.
As you select a blower speed, the blower motor switch reroutes battery power to a specific combination of one, two or all three of these resistors (within the blower motor resistor assembly).
It's this reduction in current (that the combination of resistor provokes) that makes the blower motor turn slower than full speed (HI).
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.
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|
|A||TAN||Input From HI Blower Relay.|
|B||PPL||To Blower Motor. Also Input From HI Blower Relay.|
|C||YEL||Input From LOW Blower Relay.|
NOTE: There's a good chance that the color of the wires described above DOES NOT match what's on your particular vehicle. This is no cause for concern since the circuit descriptions are the same for all of the Ford vehicles covered by this repair tutorial.
TEST 1: Checking Continuity Of The Blower Resistor
What usually happens when the blower resistor assembly fails is one of the resistor's wires burns ‘open’.
So, it's a good idea to remove it and visually check that both resistors are not burned ‘open’. If any are, then there's no need to do the continuity tests below since you've found the problem.
If the resistors look OK, there's still a good chance the resistor assembly is bad and the best way to test them is by doing few simple continuity tests with your multimeter in Ohms mode (Ω).
Don't worry, they're pretty easy to do and in the test steps below, I'll explain it all in the test steps below.
NOTE: All of the continuity tests are done on the blower resistor assembly itself. For the pin id, see image 3 of 3 in the image viewer).
OK, these are the test steps:
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: Abe's Multimeter Recommendation (found at: easyautodiagnostics.com).
Probe terminals A and B with your multimeter test leads (see image 1 of 4 in the image viewer).
Your multimeter should register continuity of about 0.2 to 1.2 Ohms. Your multimeter should NOT register OL (open loop).
Probe terminals A and C with your multimeter test leads (see image 2 of 4 in the image viewer).
Your multimeter should register continuity of about 0.8 to 2.2 Ohms. Your multimeter should NOT register OL (open loop).
Let's take a look at what your test results mean:
CASE 1: One or more of the resistors you tested DID NOT have continuity (multimeter registered OL). 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 need to replace the blower motor resistor, 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.
If your pickup's blower motor resistor passed this continuity test, you can stop here. But, if you're having a blower motor fan speed issue, I would suggest the next test. The next test indirectly tests the blower switch and blower motor relay. For this test go to: TEST 2: Checking Blower Relay Voltages.