Question about Jeep Grand Cherokee
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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Might be the Resistor pack located close to the blower. Could be under the dash or under the hood, but always close to the blower itself. Usually has a flat connector with 4 or 5 wires, and two small screws holding in the duct. It may be a crispy critter. It happens... The blower moves air across it to keep it cool. The blower motor may be bad as well, or possibly the fan speed switch. May very well be the fuse for the blower as well. The blower connector may be loose. Let me know what you find.
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Blower Motor not working for all speeds or not at all.
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:
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.
If the blower does not work at all, odds are that the problem is the fuse, relay, or the motor itself.
Repair: The resistor pack is installed in the air stream of the system to help cool the resistors. It is usually accessible from under the dash on the passenger's side or sometimes from the engine compartment along the firewall. It is identifiable by the connector with several wires coming out-some going to the switch and some to the blower motor. The resistor is replaced by unscrewing it from the duct and reinstalling the new resistor pack.
The blower is usually accessible from above the passenger
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