Forum | Marketplace | Knowledge Base | | H1 site | H2 site | H3 site
Click Here To Visit California Gold Products
Click Here To Visit California Gold Products
Click Here To Visit Adventure Accessories
Click Here To Visit Adventure Accessories
Click here for a listing of all HUMMER Network sponsors

Hummer Knowledge Base

The Hummer Knowledge Base


Heater Blower Diagnostics:


  1. No fan any speed(s):
    1. Check for voltage at A/C control module Connector A (brown) 2 (gray) and 12 (red) with ignition in run position. If voltage not present, check fuse 2C, Fuse 7D. If fuses are OK, then check wires from fuse to control head. If voltage is present:
    2. Check for grounds at A/C control Module connector 8 (black) B (black). If ground is not present fix the ground wire(s). If ground is present:
    3. Check for ground at blower motor. If ground is not present fix the ground wire. If ground is present:
    4. Apply power directly to blower motor, if motor does not run, replace motor. If motor runs replace A/C head.

  2. No fan in Low:
    1. Check for voltage at low blower relay connector 86 (brown) and connector 30 (red) with ignition in run position. If no voltage, repair or replace the red or brown wires as approprate. If voltage present:
    2. Check for continuity between low blower relay pin 85 (lt blue) and A/C controller connector M (lt blue). If no continuity, replace/repair lt blue wire. If continuity:
    3. Check for continuity between low blower relay pin 87 (yellow) and blower resistor block. If no continuity, replace/repair yellow wire. If continuity:
    4. Check for continuity (resistance) between blower resistor block pins with yellow and pink wires. If no continuity, replace/repair resistor block. If continuity:
    5. Switch the low blower motor relay with the medium blower relay. If system works in low speed now, replace the low blower (which you now have in the medium relay socket) relay. If system does not work, replace the A./C head.

  3. No Fan in Low/Medium:
    1. Check for voltage at medium blower relay connector 86 (brown) and connector 30 (lt green) with ignition in run position. If no voltage, repair or replace the lt green or brown wires as approprate. If voltage is present:
    2. Check for continuity between medium blower relay pin 85 (dk green/white) and A/C controller connector L (dk green/white). If no continuity, replace/repair dk green/white wire. If continuity:
    3. Check for continuity between medium blower relay pin 87 (orange) and blower resistor block. If no continuity, replace/repair orange wire. If continuity:
    4. Check for continuity (resistance) between blower resistor block pins with orange and pink wires. If no continuity, replace/repair resistor block. If continuity:
    5. Switch the low blower motor relay with the medium blower relay. If system works in low/medium speed now, replace the medium blower (which you now have in the low relay socket) relay. If system does not work, replace the A/C head.

  4. No Fan in Medium/High and/or High:
    1. Check for voltage at high blower relay connector 86 (brown) and connector 30 (lt blue/black) with ignition in run position. If no voltage, repair or replace the lt blue/black or brown wires as approprate. If voltage present:
    2. Check for continuity between high blower relay pin 85 (brown) and A/C controller connector C (brown). If no continuity, replace/repair brown wire. If continuity:
    3. Check for continuity between high blower relay pin 30 (lt blue/black) and blower resistor block. If no continuity, replace/repair orange wire. If continuity:
    4. Check for voltage at the resistor block, lt blue/black wire with ignition in run. If no voltage, replace/repair lt blue/black wire. If continuity:
    5. Check for continuity (resistance) between blower resistor block pins with lt blue and lt blue/black wires. If no continuity, replace/repair resistor block. If continuity:
    6. Check for continuity between high blower motor relay pin 87 (purple) and blower motor (purple). If no continuity, replace/repair purple wire. If continuity:
    7. Switch the low blower motor relay with the high blower relay. If system works in high speed now, replace the high blower (which you now have in the low relay socket) relay. If system does not work, replace the A./C head.

There are four relays in the heat A/C system:

Low Pin 30 is Red wire
Medium Pin 30 is Lt Green Wire
High Pin 30 is Lt blue/black wire
A/C Clutch Pin 30 is Brown wire

The blower resistor block has two resistors connected to three terminals. Terminal H, M and L. Terminal M is common, and you should read resistance between any two pins. This resistor block has Yellow, pink and orange. This one is used for low and medium speeds. There is a second resistor block with one resistor. This resistor block has lt blue and lt blue/black wires. This resistor block is used for medium/high speeds. There is no resistor block used for the high speed, the fan motor gets full battery voltage in this speed.

AFAIK, all four relays are identical

Peter Hipson
Founder New England Hummer Owner's Group (NEHOG) the free Hummer Owner's group!
1995 White NA Hummer Wagon


Back to main page

The Hummer Knowledge Base is a collection of informative posts from the Hummer Network forums and mailing lists, contributed material and links to outside web sites.
The Hummer Network is not responsible for the accuracy of the information contained herein or on outside web sites, nor for any situation arising from the use thereof.
2006-2011 by The Hummer Network. No material from the Hummer Knowledge Base may be reprinted or republished in any form without permission.