blower doesn't work

[zone1090]

My stepson has a 96 taurus that has a heater blower not operating. I've checked the fuses, relays, resistor, and have pulled and tested the motor itself. The fan works like a champ when I put 12 volts to it. I measured the voltage at the plug end for the blower, and have 14 volts with the car running. It drops to 6 volts when I plug the blower in,the switch seems to be fine.
Help?
John

[KimMG]

If possible by-pass the pulg. It is possible the plug may have loose or shorted connectors.

[TomV]

Originally Posted by zone1090

My stepson has a 96 taurus that has a heater blower not operating. I've checked the fuses, relays, resistor, and have pulled and tested the motor itself. The fan works like a champ when I put 12 volts to it. I measured the voltage at the plug end for the blower, and have 14 volts with the car running. It drops to 6 volts when I plug the blower in,the switch seems to be fine.
Help?
John

There is a Blower Motor relay that could have some contact problems causing the high voltage drop. I do not know haw you tested the Relay, but the high current draw of the motor calculates to a relatively low impedance. Therefore, the contact resistance of the relay must be very low or it will cause your symptom. The blower speed switch is tested the same way. Since the fuse is 40 mps I would estimate the typical current draw is about 10 amps. This calculates to a motor impedance of about 1.2 ohm (12 VDC/10 amps). This is a conservative estimate that could be even lower.

My Haynes manual indicates that the resistors have values 1.4, 1.9 and 2.4 ohms. This is very low. The contact resistance of the switch and relay have to be much lower so as not to act like yet another resistor in series with those used for actual speed control.