Your are very welcome. I am perplexed by that, very odd. That is behaving as if there is a bad capacitor in the circuit that has a, "hot at all times" fuse /power source. But there are 3 fuses for the A/C system circuit. Number 1 is a 30Amp fuse and that is for the blower motor. Fuse numbers 9 and 19 are 10 and 40 Amps and run the relays and the cooling fans.
When the fan is on full or position 4 it runs straight from the fuse to the motor to the Switch which runs to ground. There is a thermal limiter but it does not appear to have any affect in this position. In the other positions there is a resistor that has a longer path, the lower the setting. These run from power to motor to the Thermal Limiter which would act like an off switch if the circuit gets too hot, then on to the resistor and then to the switch and then to ground. I am giving you the wiring diagram as you should check the grounds for the control panel that the switch uses and any others that might affect the circuit.
If all the grounds are free of corrosion and have a good fit, then I think the blower motor resistor, which contains the thermal limiter switch, needs to be replaced. The switch is normally closed but may be sticking open and resets to closed when the fuse removes power to it. You could check this with a multi-meter by testing for voltage beyond the resitor but before the switch when the car is off and then in the ON or RUN position. If voltage is not present, try testing the fan in the full position or 4. This eliminates the resitor and thus the thermal limiter. If it has voltage then the resistor is probably bad. Even though the circuit wires pass through the resistor assembly, in the full blower switch position the resitor circuit is bypassed and just runs by the resitor and thermal switch and essentially just goes straight to ground. If there is voltage in position 4 and the fan does not work, there may be a fault in the control panel or the ground may need to be cleaned and checked.
I cannot think of another scenario that would cause this behavior.
Let me know how it goes or if you have any questions.
Friday, December 23rd, 2011 AT 3:19 PM