Fan Motor
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Joined: Aug 2008
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Fan Motor
Ok, I have a 73 F-100 and I thought the heater fan motor was out. So after about 15 minutes I got the fan motor out and just happen to skin the wires back and test it on the battery. It spun like hell, wtf? I got my volt/ohm meter and tested the plug coming out of the firewall and I get like 11.83 volts. I move the bottom slider control to off and it goes to 0 volts. I went to the engine side of the firewall took off the ground wire and cleaned screw, the firewall and the connection on the ground wire itself and put it back together. I then checked with my ohm meter the ground side of the plug on the interior firewall to the dome light switch on the door jam and it checks to be a good ground. So the motor runs at the battery but will not run on 12 volts at the plug on the interior firewall. So what next ????
Thanks Guys
Thanks Guys
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
You're checking the voltage at the plug with the fan motor disconnected which means you are testing it open-circuit, which isn't going to tell you much because no current is being pulled through the blower resistor. You're pretty much just going to see the battery. Connect the fan back up, but try to leave the plug pulled back just enough so that the fan is still connected but you can still get your meter on the power lead. Run a jumper wire out if you have to. Measure the voltage with the fan switched on and hooked up, and post the voltage you're seeing. The most likely cause of your problem is a failed blower resistor, but checking it in the way I described will tell you for sure.
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I get no rreading at all. And with the resistor pulled out you have 4 terminals, with 3 coils running between them. It seems to me that you would be able to read some kind of voltage just touching one of the 3 coils, Right? I get nothing.
When this all started my fan would not run on high, only in the 1rst, 2nd and 3rd position and then one day no fan at all. The female plug going to the fan itself looked kind of melted, so I replaced it.
With the resistor out and unpluged I can get an audible on beep (ohms 200) from my meter from the terminals that do not have coils and they do not appear to be broken .
When this all started my fan would not run on high, only in the 1rst, 2nd and 3rd position and then one day no fan at all. The female plug going to the fan itself looked kind of melted, so I replaced it.
With the resistor out and unpluged I can get an audible on beep (ohms 200) from my meter from the terminals that do not have coils and they do not appear to be broken .
