FUSE!
Check the fuses first and the blower relay.
The most common cause of the heater blower being on high only is the blower resister failing. The second most common problem is the blower switch going bad.
Blown fuse, bad heater blower motor control switch, bad blower motor, or a bad blower motor resistor pack.
The most likely cause is a bad blower motor resistor.
The most likely problem with the heater blower on your 2003 Sable is the blower resister. The resister can go bad and cause you to only have one speed.
A bad control switch can cause your 2003 Nissan Sentra heater blower to stay on. The motor or a bad sensor can also cause the heather not to work properly.
You probably have mold in the heater vent ducting.
While there are a variety of reasons your Lexus ES350 heater is not working, the most common 3 are a broken heater blower motor, a problem with the thermostat, or a failed heater blower motor resistor.
Resistor on the heater blower motor has failed
Could be, heater blower motor has failed. blower motor fuse is burned out. blower motor speed resistor is burned out. blower motor switch is bad. or, if the blower motor works but you have no heat it could be, cooling system is low on coolant. thermostat is stuck open. heater core is plugged. temp blend door actuator is faulty.
check crank sensor
can be the heater blower motor resistor located in either the ductwork or under hood near blower motor on firewall