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The blower motor relay is energized when the Blower Motor Control is set to the High position. This removes the blower motor resistors from the circuit and battery voltage is then applied directly from the HVAC BLO fuse (RH IP Accessory Wiring Junction Block) to the blower motor though the relay switch contacts. The blower motor then runs at high speed.
HVAC Blower Controls Circuit Description
The blower motor is a variable speed motor. The motor operates at a higher rate when voltage is increased to the maximum level.
The blower motor resistors reduce the voltage supplied from the A/C FAN fuse (LH IP Accessory Wiring Junction Block) when the blower control is set at low and medium speeds (speeds 1-4). The blower motor relay is energized when the Blower Motor Control is set to the High position. This removes the blower motor resistors from the circuit and battery voltage is then applied directly from the HVAC BLO fuse (RH IP Accessory Wiring Junction Block) to the blower motor though the relay switch contacts. The blower motor then runs at high speed.
Take out the temperture sensor switch and put it into very hot water to see if it works. Plug the hole with something to stop losing water. If the fan doesn't work put some voltage on the motor and try that. If that doesn't work it is the fan motor. If it does then it is a faulty switch.
check for a blown fuse first, then check the relay (you can swap out another one with it to see if the relay is bad, like the ABS or a horn relay)-if they check out ok, run a wire from the battery positive post to the positive wire on the fan connector to see it the fan runs-if so, does your temperature gauge work? If not, it is the sender unit, if it does, you fan motor is probably bad.
You can have a couple things going on. One being a bad temperature sensor. Dont be to surprised many cars have 2 and for one of them its only function is to tell the fan when to turn on. The other is a bad fan motor. Jumper a wire from the battery to the connector and see if it turns on. If it doesn't then you need a new motor.
Two possible areas I would check using an ohm meter.First is the blower resistor which is usually located by the blower motor and looks like a cement rectangle or a ceramic tube with wires attached to it. The resistor should have very low resistance but should not read open from the common lead to the other terminals. If it tests good test the continuity of the fan switch. Some cars have a fuse for the high and low blower speeds so you can check your fuse diagram and look for two blower or fan fuses. Good Luck.
You have a problem with the blower motor resistor. This is a very commen problem on all gm cars and light trucks. The part is not to pricey. You can find the resistor under the glove box buy the blower motor. Two bolts and out it comes.
With electric fans it’s almost always the fan motor. To check it run wires from the positive and negative battery posts directly to the fan motor connector. If it doesn’t run the fan motor is defective.
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