you have 2 failures and are NOT related, as posts suggests. the fan-switch or resistor block is bad , just looking at the block, with eyes, can see of the naked coils are burned up, if not,? the switch is bad, speeds bad... is SOP fix and is my heater page.
the A/C always works on high,
the fans switch blows air on high
so that sends 12vd to the A/c switch does it glow.?
if it glows, then it sends 12v to the next part.
why is this hard?
DO NOT BE TEMPTED by the DARK side to force the A/C clutch. do not.
ask how and the correct order to proceed.
the schematic is clear, see that 12v leaving the a/c switch (own a volt meter?)
see that lamp?
it can be burned out so check BLUE wire on the Amplifier . it will have 12dc on high. i bet. (it did new)
this AMP is a logic box , so you dont burn up the Compressor. see? do not
try to fool it. (fooling the over heat is ok ,if engine is not overheated , ok?)
fuses good, no brainer there.. huh.?
the next step is the clutch do you have 12vdc to it.
if you do the compressor is spinning, is it?
if not ask for help. do not bypass the clutch or the dual pressure switch
or doom awaits you.... i promise...
if the over heat switch is bad, do by pass it.
if the Hi/lo switch is open then fill the system to spec , Freon.
when that is done, then the switch closes, and the system comes on line.
ask for help.
first the electrical must work then the loop, im the guy on the Elect. side. the loop side is 100x more complex. laws and pitfalls. "ozone depletion, etc"