Heater blower does not work on settings 1 2 and 3 but does work on setting 4 do you know why?

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.

Blower motor relay , resistor , control module . any one of these could be the culprit . You have to test to determine which one is at fault ! Do you have a DVOM - digital volt ohm meter an do you know how to use it ? Heater Blower Motor Troubleshooting Blower Motor Problems Auto Repair Help

If setting 4 is high, it usually means the blower resistor has failed.

The most common problem is heater resistor defect or blower motor worn
hope it helps

SOUNDS LIKE THE SWITCH & OR THE BLOWER MOTOR RESISTOR, ARE THE PROBLEM WITH THE LOWER SPEEDS. SPEED 5 MAY HAVE ITS OWN FUSE, REFER TO OWNERS MANUAL FOR INFORMATION ABOUT THE HEATER/AC FUSE.

you need to change your blower motor resistor it should be located neer or on the blower motor housing.

Yup. Refer to your owner's manual for location. The HIGH side of the blower is fused on it's own circuit, usually a 15 AMP fuse.
Good Luck . . .

I would replace the blower resistor first. its down by the blower motor.

Your blower motor resistor has gone bad, it should be located next to your blower motor in the car, held in place with a couple of screws, remove it and replace it. The resistor is responsible for making the blower motor run at slower speeds than high or (4). Let me know if this helps.

I just had the same problem on my Nissan Xterra and the prblem is the resistor for the AC blower speed.Just get it and you will know.It is right behind and below the glove compartment and it looks like a card once you get it out. It is really easy to replace.