Question about Jeep Grand Cherokee

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Hi, I am looking fo the schematic for the heater fan blower circuit and how the fan speed switch,resisitor pack and the wiring to the motor itself are related.I dont understand where the motor physically gets its power and how the other two relate.Can you help

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  • Dennis Dietrich Mar 07, 2009

    Changed wire set. Which fuse is it on ?

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  • Jeep Master
  • 6,982 Answers

If your motor has two wires on the hot plug, one side gets power from the relay, the other gets power from the resistor pack which gets power from switch. They keep changing this from year to year, but generally that's the most comon. Best thing to do is to check both the relay and resistor for operation and check power at motor.Don't forget fuse. Unless visibally melted or burned, generally wiring does not suddenly fail. I'm usually really good at reading diagrams but have not recently found any that make any sense when compared to what I'm looking at on a particular jeep.(there may be one somewhere though!)

Posted on Jan 17, 2009

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1 Answer

Where is the resistor pack located that is in the heater circuit, for a 1998 mercury Mistique?


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Sounds like double work to me


The wd40 will only work until you have
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I would replace the blower motor &
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I like to tinker as you do, but only one time

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I only get the fan to work on high speed, the lower speeds do not work


Hi!!
The Blower Motor Resistor also called Manual Temp. Control resistor), is fried, replace. The price with floor console $25 and without floor console $65. here is a pic.
87b9810.jpg

the resistor is located on the blower motor housing, fastened by two screws. It is the part where the electrical plug connects, the plug on the pic. goes to the blower motor.
A HELPFUL - 4 THUMBS rating for this solution would be greatly appreciated. Thank you for using FixYa.

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What does it take to get air to come out the vents?

1. Power from the battery or alternator, wiring thru a fuse and possibly an accessory relay to the switch

2. Switch and wiring to channel voltage to the appropriate resistor corresponding to the desired speed

3. Resistor set to reduce voltage to the blower for settings less than high

4. Final wiring to blower and blower itself

Because there is usually no relay between the switch and the resistor, all of the blower current runs through the switch. This sometimes causes the switch to overheat and fail over time. Depending on how the switch is designed, the failure may allow multiple currents to run to the resistor pack, and this may in turn cause the resistor pack to overheat and fail. An example of the circuit I'm describing is shown below:


88d29df.gif

Note that if the above switch was to contact both terminals 2 and 3 simultaneously, there would be more current than the resistor pack is designed for. This can burn the resistors and/or blow the thermal breaker. Also note that if the resistor pack fails, the blower can still run at full speed.

Troubleshooting: The last sentence above is a clue.

If your blower is working only on high speed, the likely cause is a failed resistor pack. However, because of the other discussion above, you should also troubleshoot the switch to see if it is the reason the resistor pack failed.

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The blower is usually accessible from above the passenger

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