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John
John, Master Automotive Technician
Category: Car
Satisfied Customers: 9176
Experience:  ASE A1-A8 & L1 Master GM Tech 40 years experience
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2004 envoy: NO FAN, NO DEFROST, NO AIR, NO HEAT.

Resolved Question:

HAVE A 2004 envoy. I CHANGED THE BATTERY NOW I HAVE NO HVAC. NO FAN, NO DEFROST, NO AIR, NO HEAT. I ASSUMED IT WAS A FUSE...NOPE.
Submitted: 8 years ago.
Category: Car
Expert:  John replied 8 years ago.

HelloCustomer

Did you check the fuse block under the passenger rear seat ? HVAC1 &HVACB

Customer: replied 8 years ago.
yes hvacb was blown i replaced the fuse still nothing then i took battery cales off for 1 hour th e put back on still nothing
Expert:  John replied 8 years ago.
The HVAC B fuse is the main power to the HVAC control module.A fuse only blows if there is a short on the circuit & sometimes a voltage spike like this can take out a computer.Go to the processor & test for voltage & ground,if it is there (with the key on),use a 12 volt jumper to the blower motor.If the motor runs ,replace the processor.Test the wiring for a shorted circuit before plugging the new one in.
Customer: replied 8 years ago.
where is the processor located?
Expert:  John replied 8 years ago.

This should help.

Blower Motor Control Processor Replacement

  1. Remove the right closeout panel. Disconnect the electrical connector from the blower motor.
    Object Number: 759902  Size: SH

  2. Disconnect the electrical connector (3) from the blower motor control processor (1).
  3. Remove the blower motor control processor mounting screws (2).
  4. Remove the blower motor control processor (1).


    Object Number: 759902  Size: SH

  1. Install the blower motor control processor (1).

    Notice: Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.

  2. Install the blower motor control processor mounting screws (2).

    Tighten
    Tighten the screws to 1.9 N·m (17 lb in).

  3. Connect the electrical connector (3) to the blower motor control processor (1).
  4. Connect the electrical connector to the blower motor.
  5. Install the right closeout panel.
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