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When the blower engine resistor fails on your GMC pickup or SUV, the blower motor will only work in one speed and also in a few cases no at all.

You are watching: Test blower motor resistor with multimeter

Thankfully, experimentation the blower engine resistor is not that hard and also in this indict I"ll present you 4 different tests the will assist you troubleshoot it and also find out if it"s bad (or not).

This tutorial uses to numerous Chevrolet, GMC and also Oldsmobile pickups and also SUVs. To find out if your particular vehicle is covered by this repair tutorial, examine the box title “Applies To:” top top the appropriate column.


Contents that this tutorial:


This indict compliments this one on trial and error the blower engine resistor:

Basics that Troubleshooting The Blower motor Resistor

As you"re currently aware, her pickup"s heater manage panel gives you the alternative of 4 various blower motor speeds.

These speed are:

LO.M1 (medium 1).M2 (medium 2).HI.

The palliation in blower fan speed is achieved thru" resistors (inside the blower resistor assembly). ‘HI’ is the only blower rate that doesn"t depend on the blower resistor come function.

When the blower motor resistor fails, 1 the the 3 or every 3 first speeds prevent working. To describe this a bit further, this is because of the nature of exactly how a resistor to reduce the voltage that passes thru" it by converting several of it right into heat. This procedure causes these resistors to get exceptionally hot.

Over time and use, this resistors burn up. When this happens, one or all 3 of the very first speeds protect against working and also you deserve to (usually) remove the blower resistor and also see one (or several) of the resistor coils have actually burned and are ‘open’.

Unfortunately, periodically the individual coils look OK, but are not letting the present pass on to the blower motor. Also when this happens, troubleshooting the blower resistor assembly is still no hard and I"ll show you how in this tutorial.

The blower engine resistor"s exploit connector has actually 4 wires coming the end of it. These 4 wires it is provided it with specific signals and in the adhering to chart you"ll find a quick description that each:

Blower Resistor Circuit DescriptionsPinWire ColorDescription
AYELLO Input native AC-Heater Panel
BDK BLUOutput come Blower Relay
CTANM1 Input native AC-Heater Panel
DLT BLUM2 Input indigenous AC-Heater Panel

NOTE: There"s a good chance that the color of the wires described over DOES NOT match what"s on your particular vehicle. This is no cause for concern because the circuit descriptions space the same for every one of the GM vehicles extended by this repair tutorial.

Where to Buy The Blower Resistor and Save

The adhering to links will assist you comparison shop for the blower engine resistor:


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The very first thing we have to do is make certain that battery strength is existing in every blower fan rate selection.

By this I median that once the blower rate dial is in LO, girlfriend should have voltage in terminal A of the blower resistor connector.

Then once you turn the blower fan speed knob come M1, you must see battery voltage in terminal C and 0 voltage in terminal A of the blower resistor harness connector and so top top (for rate M2).

If battery voltage IS NOT existing where indicated in the procedures below, then the A/C-Heater manage panel has a problem.

IMPORTANT: It"s a good idea to affix a battery charger and collection it to low while you carry out the complying with tests. This will certainly avoid having your pickup"s (or SUV"s) battery getting low on charge.

OK, these room the check steps:


Turn the key to the on place and set the blower rate knob come LO.Now, verify that terminal A that the blower resistor"s connector has actually 12 Volts DC v your multimeter.


With the crucial in the on position and the blower speed knob to M1.Now, verify that terminal C of the blower resistor"s connector has actually 12 Volts DC with your multimeter.NOTE: speed M1 is the blower speed right over LO.


With the an essential in the on position and also the blower rate knob to M2.Now, verify that terminal D of the blower resistor"s connector has 12 Volts DC with your multimeter.NOTE: rate M2 is the blower speed right below HI.

Let"s take it a look in ~ what your test results mean:

CASE 1: One or an ext of the terminals walk NOT have 12 Volts once the blower fan rate knob to be turned. Repeat the tests just to make sure of your test results.

If voltage is not current where indicated in the test steps above and this missing voltage coincides with the blower fan speed that"s not working on your pickup or SUV, then you"ve uncovered the cause of the problem.

Replace the blower motor rate switch in the A/C-Heater manage panel v a brand-new one to deal with the problem.

If you want to check the blower control (speed) switch, the adhering to tutorial will present you how:

CASE 2: every 3 terminals had 12 Volts where suggested in the test steps. This is good and is the correct and expected test an outcome that tells you the the blower pan switch (in the A/C-Heater regulate panel) is OK.

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Your following step is come bypass the blower resistor utilizing a simple jumper wire. For this test walk to: check 2: making use of A Jumper wire To Bypass The Blower Resistor.