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Apr 19, 2011 | Isuzu Pickup Cars & Trucks
Jan 25, 2011 | 2001 Ford Focus
Dec 30, 2010 | 1999 Oldsmobile Alero
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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