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Weak Blower Motor


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#1 bmx_02

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Posted 15 November 2007 - 02:21 PM

I have done alot of searching on this but cant really find any definate answers or results, all speed settings on my HVAC 1-5 work but they just all seem very weak compared to any other vehicles i have drivin.. #1 setting you can hardly feel anything at all, its pretty much usless and my #5 setting is hardly enought to flip a leaf. now iv heard of replaceing the blower motor resistor but from what i hear this is usually only done when certain settings dont work at all... or could this be the problem for a weak air flow.. oh and i have cleaned the cabin filter and checked for any blockage but still got nothin.. any advise would be great

Edited by bmx_02, 15 November 2007 - 02:22 PM.


#2 M. Cueva

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Posted 15 November 2007 - 03:54 PM

I have done alot of searching on this but cant really find any definate answers or results, all speed settings on my HVAC 1-5 work but they just all seem very weak compared to any other vehicles i have drivin.. #1 setting you can hardly feel anything at all, its pretty much usless and my #5 setting is hardly enought to flip a leaf. now iv heard of replaceing the blower motor resistor but from what i hear this is usually only done when certain settings dont work at all... or could this be the problem for a weak air flow.. oh and i have cleaned the cabin filter and checked for any blockage but still got nothin.. any advise would be great



without a proper diagnosis, I would say that it is your HVAC control module, here is some reading information:


Document ID# 774868


Air Delivery Description and Operation
The air delivery controls are divided into 4 areas.
  • HVAC Control Components
  • Air Speed
  • Air Delivery
  • Recirculation Operation


    HVAC Control Components
    HVAC Control Module The HVAC control module is powered up by the ignition 3 voltage circuit. When the mode switch is rotated a variable resister in the HVAC control module changes the voltage on the mode door control circuit for an actuator position change. The module does not utilize keep alive memory (KAM). The module does not have Class 2 communication.


    Mode Actuator The mode actuator is a 5 wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5 volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5 volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5 volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts.

    The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.


    Air Speed - Front Control
    The blower motor forces outside air into the vehicle's interior. The vehicle operator determines the blower motor's speed when the driver places the blower switch in one of 5 blower speeds. The blower motor will always operate in any switch position other than OFF, as long as the ignition switch is in the RUN position. The blower motor and mode switches are located within the HVAC control module. The blower motor OFF input is connected in series with the HVAC control module by the off blower motor control circuit.

    Depending upon the selected speed, power is provided to the blower motor from either the ignition 3 voltage or battery positive voltage circuits from the fuse block. The battery positive voltage circuit only provides power when the High blower switch position is selected. Power and ground are provided to the HVAC control module by the ignition 3 voltage and the ground circuits.

    Low Blower Speed When the Low 1 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the low blower motor control circuit. Voltage is divided between 4 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

    Medium Blower Speeds When the Medium 1 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 1 blower motor control circuit. Voltage is divided between 3 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

    When the Medium 2 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 2 blower motor control circuit. Voltage is divided between 2 series resistors, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

    When the Medium 3 blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the medium 3 blower motor control circuit. Voltage is divided between a series resistor, a blower relay, and the blower motor to achieve the desired blower speed. The blower motor is grounded through the ground circuit.

    High Blower Speed When the High blower speed is selected, the HVAC control module applies voltage to the blower motor resistor assembly through the high blower motor control circuit. The voltage energizes the blower relay, causing the blower motor to be connected directly to the battery positive voltage circuit. The blower motor and blower motor relay are grounded through the ground circuit.


    Air Distribution
    The HVAC control module controls the distribution of air by the use of a defrost actuator and a mode actuator. The modes that may be selected are:
  • Defrost
  • Defog
  • Panel
  • BI-Level
  • Floor
The mode actuator is connected to the mode door by a cam type linkage system. Depending on the position of the door, air is directed through the HVAC module and distributed through various ducts leading to the outlets in the dash. If the HVAC control module detects a fault with the mode door the HVAC control module will try to drive the actuator for a predetermined amount of time, to defrost, which is the defaulted position for the mode door actuator. When the mode switch is placed in the defrost or defog positions the A/C is commanded on and the recirculation door is moved to the outside air position to help reduce window fogging. A/C is available in all modes and recirculation is only available in the panel and bi-level modes.

Mode Actuator The mode actuator is an electronic stepper motor with feedback potentiometers. The HVAC control module sends signals to the mode door actuator through the mode door control circuit. Zero volts drives the actuator in one direction while 5-volts moves the actuator in the opposite direction. When the actuator receives 2.5-volts, the actuator rotation stops. A 5-volt reference signal is sent out over the 5-volt reference circuit to the mode actuator. When you select a desired mode setting, logic determines the value of the mode actuator signals. The HVAC control module's software uses this reference voltage in order to determine the position of the mode actuator through the mode door position signal circuit. The motor moves the mode door to the desired position.

Front Defrost When defrost is selected, the A/C compressor is activated. The A/C compressor clutch will engage when ambient temperatures are above 3C (38F). The blower motor will be activated, regardless of the coolant temperature. The HVAC control module will override the auxiliary HVAC control module so a high volume of air is delivered to the front defrost vents. The rear window defogger does not affect the HVAC system.


Recirculation Operation
The HVAC control module controls the air intake through the recirculation actuator. The recirculation switch closes the recirculation door in order to circulate the air within the vehicle. The outside air switch opens the recirculation door in order to route outside air into the vehicle. Regardless of the blower motor switch position, recirculation is available only in the panel and bi-level mode switch positions. Including the OFF position. The mode switch must be placed in either the panel or bi-level position before the blower motor switch is placed in the OFF position. In order to reduce windshield fogging, outside air is circulated when the mode switch is in the defrost or defog positions. If the recirculation switch is pressed into the ON position when the mode switch is in an unavailable mode position, then the recirculation switch LED will flash 3 times. If the HVAC control module detects a fault with the recirc door the HVAC control module will try to drive the actuator for a predetermined amount of time, to outside air, which is the defaulted position for the recirculation actuator.

Edited by M. Cueva, 15 November 2007 - 03:58 PM.

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#3 Grumpy Aero Guy

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Posted 15 November 2007 - 07:36 PM

Something's definately wrong... have it checked out....

I have owned fords up until my present GMC Sierra. (Be easy on me, please. Even a blind elephant eventually finds the peanut) :crackup:

One (there are many more, mind you) of my many complaints with Fords were terrible HVAC systems. From F250SDs to Explorers to F150s...Luke warm air in the summer, blower motors that SOUNDED like you had your AM tuned between stations and your volume cranked up to "11" with insufficient air flow, and worthless AC --- even with an auxillary cooling system.

As a matter of fact, GET THIS, my '05 explorer had a "Vent" and "Bi-Level" setting... I could tell that the airflow didn't changed one iota between the two settings. Took it in. They called me, and said "checked the manuals, and, sure enough, there is NO airflow difference between the settings. Bi-Level was basically a second VENT setting. Called three additional dealers and the factory service center in my town, all of which confirmed this correct assessment. Can ya believe it????

That POS was GONE within the week... Off to GM, and NEVER looked back. I am impressed with everything about GMC.

My Sierra could be used to hang beef in it in the middle of July while sitting in the sun at idle. I get air flow tailored to exactly what I want via a fan etting I select.

You clearly have an issue which can be fixed. Take it in.

Edited by Grumpy Aero Guy, 15 November 2007 - 08:00 PM.

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#4 Chevymanfmr

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Posted 15 November 2007 - 07:52 PM

Something's definately wrong... have it checked out....

I have owned fords up until my present GMC Sierra. (Be easy on me, please. Even a blind elephant eventually finds the peanut) :crackup:

One (there are many more, mind you) of my many complaints with Fords were terrible HVAC systems. From F250SDs to Explorers to F150s...Luke warm air in the summer, blower motors that SOUNDED like you had your AM tuned between stations and your volume cranked up to "11" with insufficient air flow, and worthless AC --- even with an auxillary cooling system.

As a matter of fact, GET THIS, my '05 explorer had a "Vent" and "Bi-Level" setting... I could tell that the airflow didn't changed one iota between the two settings. Took it in. They called me, and said "checked the manuals, and, sure enough, there is NO airflow difference between the settings. Bi-Level was basically a second VENT setting. Called three additional dealers and the factory service center in my town, all of which confirmed this correct assessment. Can ya believe it????

That POS was GONE within the week... Off to GM, and NEVER looked back. I am impressed with everything about GMC.

My Sierra could be used to hang beef in it in the middle of July while sitting in the sun at idle. I get air flow tailored to exactly what I want via a fan etting I select.

You clearly have an issue which can be fixed. Take it in.


I had the same problem in my 03 s-10 nevr did work right if I recall

#5 bmx_02

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Posted 15 November 2007 - 09:36 PM

Thanks guys i think the first thing ill check is the HVAC control module im sure its some kind of resistance issue but if i get no where.... i guess ill just have to take it to the dealership :crackup:

#6 bmx_02

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Posted 15 November 2007 - 10:04 PM

dose anybody know the appropriote HVAC control module resistances for all 5 speed or any

#7 bmx_02

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Posted 15 November 2007 - 10:10 PM

dose anybody know the appropriote HVAC control module resistances for all 5 speed or any


sorry the resistors are in the blower motor resistor assembly that being said dose anybody know the resistance numbers?

#8 JNP07CC

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Posted 16 November 2007 - 10:02 AM

i had an issue similiar to this - it was the heater core was clogged with leaf debris - the HVAC worked fine - just was clogged / chocked

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#9 RyanZ71

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Posted 16 November 2007 - 08:05 PM

Take the Filter OUT and leave it out, I bet it will blow very nicely then! I took the filters out of my old 99 as well as my old Company 2000 GMC Sierra, and MAN what a difference!

They do not put those filters in the 2004+ I believe...