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Old 08/21/09, 11:34 AM   #1
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heater blower resistor

one of my customer's resistor has gone out on his heater blower motor. would it be the same voltage drop as a resistor for an ignition coil?
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Old 08/21/09, 12:59 PM   #2
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No, it's a different type of resistor, and is designed to reduce current to the fan for different speeds. Usually those blower speed resisters are mounted in the heater duct.

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Old 08/21/09, 01:32 PM   #3
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An ignition resistor would catch fire if you tried to use it with the blower. But you can use almost ANY blower resistor (any make/model/year) if you have the matching connector, and can make it fit in that duct.

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Old 08/21/09, 01:50 PM   #4
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good to know, thanks guys. my knowledge on resistors is minimal unfortunately. anybody have a good used one?
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Old 08/21/09, 05:12 PM   #5
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The blower motor uses more current than the ignition coil so the resistor needs to have a higher wattage capability.

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Old 08/21/09, 09:14 PM   #6
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Quote:
Originally Posted by 73stallion View Post
anybody have a good used one?
I bet your local junkyards have a few.
Quote:
Originally Posted by Viperwolf1 View Post
The blower motor uses more current than the ignition coil so the resistor needs to have a higher wattage capability.
...and more resistance.

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Old 08/21/09, 09:34 PM   #7
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well, gotta hit the wrecking yard this week for a new set of visors for the CR-V, so i'll look around for one. thanks again!
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Old 08/21/09, 09:45 PM   #8
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Quote:
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I bet your local junkyards have a few. ...and more resistance.
I bet the resistance is pretty close. Within a couple ohms.

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Old 08/21/09, 11:53 PM   #9
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Well, it'd have to be since the ig. resistor is only 1.05-1.15 Ohms; the M2 blower resistor is .25; M1 is .55; L is 1.3 , and they're added (so M1 speed uses .8 Ohms; L uses 2.1).

Since the blower draws ~20A, the resistors have to dissipate ~50W of heat.

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Old 08/22/09, 12:36 AM   #10
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Quote:
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Since the blower draws ~20A, the resistors have to dissipate ~50W of heat.
Hey Steve, is that last number (50w) correct? I didn't follow each of your numbers and equations, but the rating seems low, since the Mallory ignition ballast resistor is rated at 200 watts.
Is it just that we're talking about current on the one hand, and heat on the other? Or are they one in the same in this case? And if so, would that 200w rating then be sufficient?

I'm not recommending a full-size resistor in place of a true heater-resistor. I'd use a standard heater type, even if only for convenience and safety (with the coils inside the plenum air stream), but it would appear to at least be a functional alternative from an electrical standpoint at least.
Which is why I'm asking.

Thanks

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Old 08/22/09, 09:41 AM   #11
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I did some quick calculations last night, so I might have goofed, but I think it's right. It seems about right.

Current (Amps, "i") isn't heat; it's the flow rate of electrons. Heat (Watts, "W") is power lost/wasted. Voltage (Volts, "V") is the 'pressure' of electricity. Resistance (Ohms, "R") is the 'friction' of electricity. V = R * i ; W = V * i = R * i * i .

My '83 never had a resistor, and I don't remember what was in Frank's '75, so it surprises me that yours is a 200W. If so, it SHOULD work fine, as long as it's in free or forced air (so it can lose that heat), AND your connections can take the heat. If you confine it in a wiring harness or even wrap it with tape, it'll start a fire. That's why all blower resistors are built to go in the airstream, and are bare. Your ig. resistor is probably ceramic-cased, right?

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Old 08/22/09, 10:26 AM   #12
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man, you guys lost me a long time ago with amps vs watts, i never did learn that.
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Old 08/22/09, 11:13 AM   #13
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man, you guys lost me a long time ago with amps vs watts, i never did learn that.
Just wait 'till he starts talking calories then!

Paul
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Old 08/22/09, 11:23 AM   #14
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Quote:
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My '83 never had a resistor, and I don't remember what was in Frank's '75, so it surprises me that yours is a 200W.
Did they just regulate it directly in the switch then? Or is there another method of resistance used there? Just curious. Might come in handy someday to know that.


Quote:
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If so, it SHOULD work fine, as long as it's in free or forced air (so it can lose that heat), AND your connections can take the heat. If you confine it in a wiring harness or even wrap it with tape, it'll start a fire. That's why all blower resistors are built to go in the airstream, and are bare.?
Definitely! That's what I was suggesting when I said it might be "less convenient and safe" to mount a non-standard type in anyplace other than the original location. It's just way bigger than a standard heater version. But "could" be used if you did it carefully.


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Your ig. resistor is probably ceramic-cased, right?
Yep, just a standard resistor and looks like any other one you've seen for the last 50 years or so. May just be "updated" with heavier components. In the text, they seem to be claiming that it's "variable based on ambient temperature", if I'm reading their add-type correctly, but it seems to me that all resistors are temp-variable. Wouldn't they be?
I can send you the image and text from the catalog if you want to check it out or post it here for the others.

Paul
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Old 08/22/09, 11:28 AM   #15
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Quote:
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Just wait 'till he starts talking calories then!

Paul
no i know how to count those, i just don't (enter guacamole bacon six dollar burger here).....
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