My fan switch is not working on the 1, 2, and 3 settings. it only works on the 4 and 5 settings. Is this a fuse problem, fan switch problem or heater fan problem?

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.

Does it work on any setting? Like 1 2 3 or 4?? If only works on say...4 then it's your resistor in the switch. Not bad easy fix. YouTube or Google it. You'll see

problem in your blower switch

You must have a problem in the fan circuit, either the fuse, the relay, power to the relay, or the sensor. Easiest place to start is the sensor, on Toyotas of his vintage the sensor is wired so that if it is unplugged the fans will turn on (providing the ignition is switched on) Look to the bottom of the radiator, there will be a sensor with 2 wires. Unplug the sensor and turn the ignition to ON. If the fans go, the sensor is faulty, and is he cause of you fans not turning on when the engine heats up. If the fans remain off, the next thing to check is the fuse. In the fuse box under the bonnet you should find a fuse or fuses labeled fan No. 1 and fan No. 2 (if air conditioning is equipped) NOTE these are sometimes labeled RDS and CDS The labels are on the underside of the fuse box cover. Check the fuse/s by either looking through the top if they are the square type, or pulling them out and looking through the side if they are the blade type. If none of these fuses are blown there is an electrical fault that requires some electrical knowhow to diagnose. The problem could be a blown AM1 or AM2 fuse, which you could also check, these are the battery feeds from the ignition switch to the rest of the car. Usually a blown AM fuse will mean other electrics will not be working either. Another possibilty is a stuck relay, though highly unlikely, as they usually fail to work, meaning the fans will be constantly on. They're named fan No.1 and Fan No. 2 usually You really need to understand how a relay works to check if there is a problem, for instance you can check if the relay coil is being energised by using a test light across the pins in the socket when the relay is removed. You can also check that ignition voltage is being supplied to the contacts of the relay while it is removed. Toyota relays have numbers 1 2 3 4 & 5 for the pins on them. There is usually a small diagram on the relay to tell you which pin is which number, and possibly which pins are the winding and which are the switchable contacts aswell. In general, pins 1 & 2 are the winding, or activator in easier terms, and pins 3,4 & 5 are the switched contacts. Pins 3 &4 are usually common and are disconnected & joined with pin 5 when the relay is energised. NOTE some relays exclude pin 4, and some replace pin 5 with pin 4, leaving only 4 pins in total.
To check the fan circuit with the relays removed, bridge across the sockets where pins 3 & 5, or if it only has 4 pins, pins 3 & 4 and the fan should turn on with the ignition switched on. If not, there is a problem with the ignition circuit.

You'll have to find the correct wiring diagram in order to trace down the fault in your system.. Once you obtain the wiring diagram you'll be able to see what else beside wire is between the #4 speed setting and the blower motor. My guess is you might find a high speed fan relay is triggered from the #4 fan switch setting, applying full battery voltage to the blower motor. If locating the appropriate diagram proves to be difficult you can try looking around the underhood and passenger compartment fuse panel to find a relay. Keep in mind not all relays are always in fuse boxes which makes the diagram important.

common problem, replace the blower motor (fan) resistor, this is what controls the fan speed,its located on heaterbox next to blower motor.heres a picture of it,its on the rightside of dash toward the bottom. hope this helps.

these systems use a resistor pack,setting 1 2 3 go through resistors to vary fan speed, 4 is fast speed-- no resistor in circuit. don't know where it is located but usualy in aplace it can get cool air, try follow the wires back from the fan motor to the switch.

A resister near the fan - check with Auto Zone, they might find it for you.

it sounds like the fan speed switch ...but im no expert