HVAC Blower Relay 13 (Underhood fuse block)
Hi Blo Motor Fuse 53 (Underhood fuse block)
Hi Blo Motor Fuse 53 (Underhood fuse block)
HVAC Blower Fuse D (Right instrument panel fuse block) not shown here.This fuse D is in the instrument panel fuse box.
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Electric current supplied by the battery is routed through fuse D, and then to the fan speed selector switch. If the switch is set to 5 (high), the current gets directed to the control side of the realy #13. The relay trips and connects power from fuse 53 directly to the blower motor. If the speed selector switch is set to any other fan speed (1-4), current gets directed through the resistor pack, then to the "normally closed" side of the (un-tripped) relay #13 which routes the power to the blower motor.
Conditions where fan speed 5 would fail but speeds 1-4 work:
1) Fuse 53 blown
2) Relay won't trip because it is stuck. You can bench-test this.
3) Relay won't trip because there is a bad ground on the control side.
4) Relay trips but won't connect because it is badly pitted. Difficult to bench-test because it requires a load in the circuit to make a determination.
5) Switch is bad.
Conditions where fan speed 5 would fail but speeds 1-4 work:
1) Fuse 53 blown
2) Relay won't trip because it is stuck. You can bench-test this.
3) Relay won't trip because there is a bad ground on the control side.
4) Relay trips but won't connect because it is badly pitted. Difficult to bench-test because it requires a load in the circuit to make a determination.
5) Switch is bad.
You can try swapping relay 13&15 because they're the same relay and see if that works.
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