1998 Isuzu Rodeo is having issues.

A mechanic would check for voltage at the blower motor, the resistor, the relay, and the fuse.

just unplug the fan motor and connect a tester with a light bulb to it turn the fan control on and watch for the light to get brighter as the speed goes up, if it does replace the fan motor . if not check fuses and power to the switch itself.good luck

sorry to say but sounds like heater core needs replaced might try back flush and see if that helps but it most likly wont help much but will let u know for sure if that is problem because it will help alittle (after all it dose take alot of time to change core) hope it helps

check your IAC or stepper motor operation run the vehicle with the AC on and see if its makes a difference

could be a plugged up heater core. need more info about what your vehicle is doing

Thermostat! or blockedf heater matrix, no idea where the thermostat is on that car never worked on one.

hope this helps

The resistors are in circuit only on the lower fan speed settings.
On the highest speed setting, power is switched directly to the fan motor.
Check fan power supply fuses,
Check power is available to the fan when high speed selected.
If all above OK, apply power directly to the motor to verify fan motor runs- if it doesn't the motor may need replacement/repair.

look on the y pipe just in front of the cats.......

System needs to be recharged with R134 freon

Get a new blower motor and relay.