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Wrong, wrong, wrong Posted by Ari [Email] ![]() ![]() In Reply to: Blower motor or Fan problem ?, Yoni, Mon, 28 Jul 2003 12:02:49 Members do not see ads below this line. - Help Keep This Site Online - Signup |
It does sound like the fan, but I don't trust your mechanic. It's not that he's evil, but one of his conclusions was wrong.
I'm assuming your car has ACC (non-manual temp and fan controls). The fan speed is controlled by a transistor. But if the fan isn't working, varying the fan speed won't vary the voltage at the fan. What? The fan speed controller is designed to work with the large electrical load of the fan - 15-25 amps. Let's assume that the fan just has an open circuit. A voltmeter pulls microamps at most. There would be no current draw across the transistor, so it's going to be battery voltage at any speed but off. And probably even at off, due to leakage currents.
A better test is to hook 12 volts from the battery AND ground from the chassis directly to the fan. If it spins, that's a good sign for the fan. If it doesn't, then the fan is toast. Yes, replacing the fan is a pain, not because of the cost of the parts, but the labor involved. For a '90 car, I would also replace the heater core, because if it's not leaking now (doubtful), it will soon. Yeah, spending more money isn't a happy thing, but it'll be cheaper if you intend on keeping the car.
However, you might very well have a perfectly good (or at least decent) fan. Not very likely, but possible. There could be a problem with the controller. IF the mechanic measured the voltage to the fan while the fan was hooked up, and saw 12 volts, then it's probably the fan. But if the fan wasn't connected, there could be a bad connection in the controller, or a bad pass transistor. It would provide 12 volts into the neglible load of the meter, but may not have enough current to start the fan motor.
Again, the test is to hook a known 12 volts and ground to the motor and see if it spins.
posted by 192.249....
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