heater not working right any suggestions???

i got a 90 4runner with a 22r lastnight the heater stopped working completly so today i changed the fuse now it works on low and medium but wont go on high any suggestions to fix this??? thanks guys

Electrical will be only the blower.
The hot water flows through a valve found on the fire wall, operated by a cable.
Check the cable & the valve ( remove the hoses each side & run water or blow air through )!

the most common thing is the blower restitor if its not working on high speed