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This is more likely to be a bad switch, if you only have the lowest speed. The switch has several positions, in each position another resistor in the resistor block is added into the circuit. ANy open resistor makes the blower not work from the point when the open resistor is switched into the circuit, as well as all subsequent speeds from tht position on.
In the lowest speed, all of the resistors in the assembly are used to drop voltage to the blower motor to make it run as slow as possible, therefore there are no open (failed) resistors. The problem is either a switch that is not making electrical contact in the other positions, or a broken wire somewhere. Also note: in high position the resistor block is bypassed entirely, and full 12 volts is fed to the blower motor from the switch; so if you have no high speed either it is not possible for the resistor assembly to be responsible since it is not used in the circuit in that position.
Therefore the posting from the other specialist is obviously incorrect and replacing the resistor assembly will be a waste of money and will not correct the problem. The switch is the likely failure for the symptoms described.
If this is helpful, clicking my accept button would be most appreciated.... thanks!
Please ignore this second specialist's futile attempt to discredit my answer. He is wrong and trying to sound right. Switches DO NOT generally drop some speeds and not others. I stated both were possible and it can be tested easily using a ground testing, testlight. Simply test for ground signals arriving at different wires on different settings at the resister plug. If all the ground signals arrive for the speeds in question, the resister is bad. If not the switch is bad.
Please ignore the other disgruntled specialist's attempt to hijack the question and click on the accept button for MY answer.