Heater fuse blow every time I turn it on.

[Her62Tbird]

Well it's getting cold and I would love a heater. Everything is working fine just replaced the motor. Test lighting comes back hot everything should work fine. Once you plug into on/off controls it frys a fuse.

[novanutcase]

Check your grounds....

John

[ABQTBird]

Well it's getting cold and I would love a heater. Everything is working fine just replaced the motor. Test lighting comes back hot everything should work fine. Once you plug into on/off controls it frys a fuse.

What year car and does it have A/C? Make sure you are using a 14A fuse in the box. What happened with the old motor? Did it run at all? Does the new motor cause the fuse to blow immediately, or after some time, and if so, at what fan speed is the motor blowing the fuse? To blow a fuse, the motor is drawing too much current. This would be especially true if the fuse is blowing right at startup since DC motors draw a lot of current at startup and then drop back down to baseline when up to speed. I would get a voltmeter rather than a test light and test for voltage at all three speeds. Unfortunately, most meters only go up to 10A for current testing. As a test, you could replace that 14A fuse with a 20A and see what happens. I don't recommend that as a permanent solution though. This is not caused by a bad ground. On the contrary, a bad ground would result in less current flowing to the motor as it acts as a resistor.

Have you bench tested the motor? I use an old computer power supply for bench testing. Lacking a power supply, you could hook it directly up to the battery to see if it spins. Use some heavy-duty clip leads, 18AWG or larger (smaller in number) and be cautious for hot wires.