cars78md

THE HEATER FAN SWITCH IN MY 1978 CORVETTE WORKS ON THE FIRST THREE SETTING FINE,ON THE HIGH SETTING SOMETIMES IT WORKS AND SOMETIMES IT DON"T. ANY IDEA"S.....

mark6669

Check the high blower relay on top of outside evaporator box.
Mark

pancake

I had the opposite problem.. but the fix is the same. Disconnect the plug, pull the relay, and pop the cover off of it.. and take an emery cloth or fine grit sandpaper and lightly clean both sides of the contacts. You don't have to do much and it'll work just fine.

menardd

Had the same problem, I replace the relay still did not work highest speed other speeds work. I took the cover off of relay left wires on it touch down on contact point and the high speed worked????May be the new relay was defective??

mark6669

Check for ground on black wire on relay with volt ohm meter and for 12 volts on pink wire with fan switch on high speed ( pink is from 77 wiring diagram not sure if same in 78 but probably is).
Mark

dmrodco

just fixed mine today it was the relay check to see if you have 12VDC on the pink wire when the switch is on high if it is then its the relay of not the fuse in line with the pink wire is bad.