Blower Motor Relay Test (1991-1993 2.8L Chevrolet S10 Pickup, GMC Sonoma)

TEST 4: Jumpering Connector Terminals B And E (HI Speed Circuit)

If you've reached this point, you have confirmed the following:

• The blower relay is getting 10 to 12 Volts DC (TEST 1).
• The blower relay is getting Ground (TEST 2).
• The blower relay is getting its activation signal on terminal C of the relay connector (TEST 3).

Now, we're gonna bypass the blower motor relay and activate the blower motor in HI speed.

This test simply involves jumpering (connecting) connector terminal B to terminal E.

If the wiring between the connector and the blower motor is OK, connecting both terminals should activate the blower motor to run at HI speed.

IMPORTANT: Before testing the blower motor relay, make sure that the blower motor itself is OK. This tutorial will help you test the blower motor (if you haven't already): How To Test The Blower Motor (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).

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 E of the blower relay connector together using a jumper wire (see illustration above to identify the terminals).
   
   Terminal B has a purple (PPL) wire connected to it.
   
   Terminal E has a red (RED) wire connected to it.

3. 3

   The blower motor should run in HI speed as soon as you jumper both female terminals of the connector.

Let's examine your test result:

CASE 1: The blower motor ran in HI speed. This is the correct and expected test result.

If the blower motor does NOT work in HI (with the relay connected to its connector), but does work when you jumper terminal B and E, then you can conclude that the blower relay is defective and needs to be replaced.

If the blower motor does not work in LO, M1, and M2 but does work in HI (with the relay connected to its connector), then your next step is to go to: TEST 5: Jumpering Connector Terminals B and D (LO, M1, M2 Speed Circuit).

CASE 2: The blower motor DID NOT run in HI speed. If have tested the blower motor by directly applying power to it, then this test result usually means that the purple (PPL) wire between the relay connector and the blower motor has a problem.

Your next step is to check the continuity of the purple (PPL) wire. If the PPL wire does not have continuity, then you've found the problem that's causing blower HI speed to not work. Repair the open in the PPL wire.

TEST 5: Jumpering Connector Terminals B And D (LO, M1, M2 Speed Circuit)

In this last test section, we're gonna jumper relay connector terminals B and D together.

In case your wondering:

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

Once terminals D and B are jumpered together, we'll select blower speeds LO, M1, and M2 from the AC-Heater Control Panel.

If all is OK, you should see the selected blower speed running with the jumper wire connecting terminals D and B.

IMPORTANT: The blower motor itself must be in good condition before performing 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 (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).

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 brown with white stripe (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).

More 2.8L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials

You can find a complete list of tutorials for the 2.8L V6 Chevrolet S10 pickup, GMC S15 pickup, and GMC Sonoma in this index:

• GM 2.8L Index Of Articles.

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

• How To Test The Fuel Pump (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
• How To Test Engine Compression (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
• How To Test The EGR Valve (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
• How To Test The Starter Motor (1988-1993 2.8L V6 Chevrolet S10 Pickup, GMC S15 Pickup).