Problems with a blower motor resistor are common in many cars. The most common symptom of a failed blower motor resistor is when the heater fan only runs at the highest speed setting (4 or 5) and doesn’t work at low speeds. In some cars, a failed blower motor resistor can cause a heater fan to stop working completely.Aug 1, 2021
In the highest speed state, the blower resistor is bypassed completely and the fan is connected directly to the car’s battery, which allows maximum current through the motor. Power to the blower motor is fed through the blower motor resistor, so if it fails or has any issues power can be cut off to the motor.
Power to the blower motor is fed through the blower motor resistor, so if it fails or has any issues power can be cut off to the motor. A blower motor without power will not be able to produce any air pressure, and as a result the heating and air conditioning system will be left with no air coming from the vents.
Trent, one of the biggest reasons for blower motor resistors to have shorten life is actually because of faulty blower motor drawing too many amps, some times melting wires/plugs, heating up resistors shortening their life.
Blower works on slow speeds, but not on high speed
Check for bad fuse or bad high speed relay. Swap the high speed relay with another relay with the same part number. Also, check the fuse for the control side of the high speed relay. Make sure the ground side of the high speed relay is working.
In a blower motor, the relay supplies the power that allows the fans to circulate warmed air. Essentially an on/off switch, the blower motor relay’s reactions start and end the heating process in HVAC systems by controlling the flow of current between the power source and the motor.
When a blower resistor fails, the highest fan speed usually is the only one that still works because it essentially bypasses the resistor and receives the maximum amount of voltage. When the resistor is working, it reduces the amount of voltage going to the lower fan speeds, so the fan runs slower.
The fan switch may be at fault, but a more likely reason is that a blower motor resistor that controls the voltage going to the blower has packed it in, resulting in only one speed remaining operable – usually the highest speed. …
This would be normal. Many blower motor resistors are designed such that they would burn up if they are not in the path of the air from the blower fan.
When a resistor has been overloaded with voltage exceeding its power rating, the resistor will become very hot to touch, darken considerably and possibly even melt or catch on fire. … However, it may be functioning with less resistance than it was originally designed for.
Using a multimeter set on the Ohm scale, use the positive lead and test the black wire. To check the purple wire for current, use your ignition key and turn it to the run setting, turn the heater power to full power and set the multimeter to DC power. If your meter reads “no current” the motor is no good.
It sounds like this may be a sign of a faulty blower motor or bad wiring between the motor and the resistor. … The electrical contacts may also wear out causing the motor to fail. I would recommend having an expert from YourMechanic come to your location to diagnose and replace your blower motor.
Connect a test light or multimeter to the ground (black lead). Turn the ignition key to the on position (engine off), and remove the relay. Using the probe, test all terminal sockets in the relay connector. Two of the four should have power.
The fan switch usually has two settings: auto and on. Switch the fan setting to “on,” instructs Fireplace Hubs. Listen for the sound of the blower turning on. Check that air is being sucked into the cold-air returns and being blown from the warm-air registers.
A fuse is often located on the resistor board. The fuse only protects the low and medium blower speeds.
Many vehicles have two fuses for the blower motor, one in the interior fuse block and the other under the hood. The blower motor is usually under the dashboard on the passenger side.
Common warnings signs that your furnace control board is bad include warning lights on your furnace’s diagnostic system (see step 1 below), temperature instability (significant fluctuations in temperature, especially when the thermostat is ok) and interruptions in the normal sequencing of your furnace.
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