TEST 4: Jumpering Connector Terminals B And D (LO, M1, M2 Speed Circuit)

How To Test The Blower Motor Relay (1991, 1992, 1993 2.8L Chevy S10/ GMC S15)

In this test section, we're gonna' jumper relay connector terminals B and D of the blower relay connector.

Terminal D has a dark blue (DK BLU) wire connected to it. Terminal B has a purple (PPL) wire connected to it.

Once terminal D and B are jumpered together, we're gonna' activate blower speeds LO, M1, and M2 and see if they work.

IMPORTANT: The blower motor itself has to be functioning OK before doing the test in this section. This tutorial will help you test the blower motor (if you haven't already): How To Test The Blower Motor (2.8L Chevy S10/ GMC S15).

WIRING DIAGRAM: You can find the blower motor circuit diagram here: 1991-1993 2.8L Chevy S10 Blower Motor Circuit Diagram.

These are the test steps:

  1. 1

    Disconnect the blower motor relay from its electrical connector.

  2. 2

    Jumper terminals B and D of the blower relay connector together using a jumper wire (see illustration above to identify the terminals).

  3. 3

    Turn the key ON and place the vent control switch in any vent position that is not OFF.

  4. 4

    Place the blower switch in LO fan speed. The blower motor should run in LO speed.

  5. 5

    Place the blower switch in M1 fan speed. The blower motor should run in M1 speed.

  6. 6

    Place the blower switch in M2 fan speed. The blower motor should run in M2 speed.

Let's examine your test result:

CASE 1: The blower motor ran in LO, M1, and M2 speed. This is the correct and expected test result.

If blower speeds LO, M1, and M2 do not function with the relay connected to its connector, but does work when you jumper terminal B and D, then you can conclude that the blower relay is defective and needs to be replaced.

CASE 2: The blower motor DID NOT run in LO speed but ran in M1 and M2 speeds. This test result eliminates the blower relay itself as bad.

The most likely cause of this no LO blower speed is an open in the BRN/WHT wire between the blower resistor and the vent control switch (see the circuit in the wiring diagram here: 1991-1993 2.8L Chevy S10 Blower Motor Circuit Diagram).

Where To Buy The Blower Motor Relay And Save

You can find the blower motor relay in any auto parts store. If you're wanting the buy the original AC Delco blower motor relay, you can buy it online for a whole lot cheaper than somewhere local.

The following links will help you comparison shop for the blower motor relay and hopefully save you a few bucks:

More GM 2.8L Tutorials

To see all of the 2.8L S10/S15 specific articles, go to: GM 2.8L Index Of Articles.

Here's a sample of the articles you'll find in the Index of Articles:

  1. How To Test The MAP Sensor With A Multimeter (2.8L Chevy S10, GMC S15).
  2. Vacuum Hose Routing Diagram 1988 GM 2.8L S10/S15.
  3. How To Test For A Bad Alternator (2.8L V6 S10/S15).
  4. How To Test Engine Compression (2.8L S10 Pickup/Blazer).
  5. How To Bench Test The Starter Motor.
  6. How To Test The Starter Motor On the Car (Step by Step).
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