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2004 Lesabre no heat

11-29-2014, 03:04 PM
A few weeks ago my battery died and I had to jump start my car. After the jump start, my heat wasn't working - no air will blow out on heat or A/C. I checked the fuses - all good.

I pulled the blower motor out and tested it and it worked hooked up to a battery. At one point when the blower motor was still in the car I banged it with a hammer and it turned on momentarily then shut off again.

Since the blower motor seemed to work outside of the car, I assumed it was the resistor that was bad. Replaced that today, and still no heat.

Could the blower motor be bad and just have worked hooked to a battery intermittently?

What else could it be?

Blue Bowtie
11-30-2014, 10:55 AM
Welcome Aboard!

The blower is controlled by several items. The main power feed from the interior fuse panel via a 30A fuse. If this is intact there should be 12V at the orange wire at the blower control module/resistor. Without this supply the blower will not operate at any speed.

In addition to the power feed, there is also an instrument panel integration module which receives signals from multiple inputs including the heat/cool control module HVAC module), at least five interior temperature sensors, the sunlight sensor, and the vehicle powertrain control module. This integration module also controls the air delivery damper stepper motors, the blower control module, and the AC compressor.

The blower control module/resistor needs to receive signals from the HVAC control module in the instrument panel through the integration module. This control panel can become out of synchronization with the air damper and temperature control modules if power is lost on the vehicle. The control panel will stop or vary the blower speed is the HVAC system is not within some limits relative to the temperature and function settings. In other words, if the control panel is set for maximum heat (90) and the engine coolant temperature is below about 150F, the control panel will refrain from operating the blower since the system cannot deliver heated air to the vehicle interior. A similar thing happens when a cooling setting is selected and the evaporator pressure is too high for the system to presume the AC compressor is running properly. The passenger side zone controls also signal the control module and affect its operation.

In short, verify the power source. If it is present, start the vehicle and allow the engine to reach full operating temperature. Set the HVAC controls for full heat, and wait several minutes for the controls to synchronize. Then set the HVAC controls to full cool, and allow several minutes for the controls to synchronize. At some point in either of these cycles the blower motor should vary its speed.

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