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Discussion Starter · #1 ·
I have a question for all of you. My heater fan only runs on high. I switched out the fan switch and it worked for twenty minutes after which I shut it off and went into a store. When I came back out again, my heater fan was only working on high again. Can anyone give me ideas of what to look for?
Need to go to Alberta Monday morning.
 

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Does the same for me. I replaced the switch I can't think of the name but it went out again.

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Discussion Starter · #3 ·
Yeah, I should have said resistor. I also read that if the air filter beneath the windshield is plugged or real dirty, the resistor may blow so I replaced that. Does anyone else know anything I should check before I put a resistor in the car. I'm hoping it won't blow again.
 

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Motor could be failing and when you put it on low the motor is pulling to hard which could be burning up the resistor. Happened on business truck a few times and they replaced the motor and hasn't ever happened again. Just more ideas for you, not saying I'm 100%.


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Now I'm no expert, but mine would only go on 3 and 4 speed.
Replaced this resistor unit. Got a new one from ebay I think.
The one in the photo is the old one which I repaired first to see if it was the problem, it was.:thumb:
 

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Discussion Starter · #6 ·
I put in a new one which ran good for about 20 minutes. Then I went into a store and came out in 15 minutes and the blower was only working on high again. Any ideas as to why the resistor would go so soon?
 

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I put in a new one which ran good for about 20 minutes. Then I went into a store and came out in 15 minutes and the blower was only working on high again. Any ideas as to why the resistor would go so soon?
If it has gone again I would say the blower is drawing to much current or a bad connect on the resistor plug. It could be to much load or faulty blower motor. If you have checked the filter then I would spin the blower by hand to see how easy it spins.
Maybe bearing or bushes dry.
 

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The motor pulls harder when it is running slower? I'm not sure I understand that one.

Yuh it's pulling higher amperage through the resistor if the motor is failing. When it's on high its not getting forced to transfer the high amperage.


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Discussion Starter · #11 ·
Well, I replaced the air filter through which the fan pulls air to supply the inside of the car (forget what the air filter is called. I'm 60 and I rarely remember names for anything for longer than 5 minutes.) And I replaced the fan and put a new resistor in it and then drove 10 hours to Alberta with the fan on low and it worked great all the way. Thanks for all your great help.
 

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The motor pulls harder when it is running slower? I'm not sure I understand that one.
Old school and simple electronics. Many heaters, especially Fords, only have one speed which creates a certain load. This is high or the maximum speed the fan will rotate. To give it more than one speed they place resistors in series to slow the fan down. Like tying a loose not in a garden hose. That gives you medium. To make it run slower you have to put another resistor, or tighten the knot, in series. This gives you low. Each time you put another resistor in line to slow it down it adds more resistance to the line. To get through the resistor more amperage, or pressure, is drawn thus creating more current flow through the heater line. Therefore when the heater is on low it is drawing the most current. When its on high it draws the least current. When it only runs on high its because the resistors have shorted out for some reason. Clogged filters will make the heater work harder because it can't draw as much air past the fan. Dirt in the motor bearings will also slow down the motor so the motor will work harder pulling more current and blowing the resistors as the current exceeds the rating of the resistors. Heaters have worked this way since the 40's. See? Easy Peasy.
 
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