Rebuilding heater resistor

[Pdxguy]

Trying to clean up the resistor I have, one of the coils is broken. Could this type of resistor, matched to the needed voltage, resistance, etc be used? I'm guessing there is less heat generation as well. 

 

Thanks,

Dennis

 

[jimk]

2 minutes ago, Pdxguy said:

matched to the needed voltage,

Amperage is the issue.

[calw]

Lots of different resistor styles would work. But you need the right specs- resistance and power rating.

 

The coil of nichrome wire that was used originally was the cheapest thing available.  When substituting something else in, the key is to get the right resistance, which in conjunction with the blower motor's resistance sets the current thru the two.  Also, the resistor has to be able to withstand the power that's being dissipated in it. 

 

"less heat generation" isn't gonna happen though- the power dissipated in any resistor comes out in the form of heat.  The resistors in the photo look like they have a power rating of  1/4 watt or so, much less than is needed. You could simply replace the wire coil with a bit of copper wire in order get going, but the fan would run at full speed. 

 

I did a post related to using a different fan motor a few years ago which had current measurements in it, but I don't recall measuring the resistance of the wire resistors, and my heater's back in the car now.  With those two facts, one could calculate the power rating of a replacement resistor.  It's only a few ohms but to get the right blower speed  you'd need to match it reasonably well.  Hopefully someone can measure the resistor in an open heater box.

[John76]

The resistors are 2.5 Ohm (low speed) and 0.75 Ohm (medium speed) for the 3-speed blower.

Direct connection to ground without any resistance is the highest speed.

 

[wheelieking]

It looks like @John76 has it covered above, but I have my 3-speed heater box out and in the middle of refurbishment in case anyone wants me to check/test anything.  I hadn't even thought about replacing resistor components though, I'm interested to see if that is possible. 

[jimk]

Diagram doesn't match any of the OE diagrams I have.  All diagrams are the same and the resistors are in series with the motor windings.

[dlacey]

You need a resistor that can dissipate the power... its common for car blowers to have 'open air' resistance coils cooled by the blower airflow, later designs have the resistors in an alloy block. If you dont care for originality, but want a rugged solution to permanently fix the issue, use two chunky 50W resistors screwed to a metal heatsink like these:

They are readily availble in the resistances you need. I have done same on other cars with good success.

[John76]

4 hours ago, jimk said:

Diagram doesn't match any of the OE diagrams I have.

You're right Jim!  

At least you can read and understand mine.😁

John

[Mike Self]

Unless you accidentally broke one of the electrical terminals on your resistance board, your old one should work, primitive as it is.  I've not heard of one actually burning out electrically, just having a terminal break off.  Have you tried soldering the broken wire?

 

mike

[dlacey]

3 hours ago, John76 said:

7 hours ago, jimk said:

Diagram doesn't match any of the OE diagrams I have.

You're right Jim!  

At least you can read and understand mine.😁

John

There was quite a change in the wiring for the >73 cars

<73 cars have the twist/pull switch next to the instrument cluster, the switch has 3 12V outputs that connect to the resistor pack on the Blower/Heater assembly.
>73 the blower control is now on a slider beside other heater controls, the slider has three switched ground wires (per @John76's  Diag) that connect to the resistor pack and there is one 12V feed to the blower.

So, they moved the resistor pack from being in series with the 12v supply to being in series with the switched ground when they came-up with the slider fan speed control.

[jgerock]

The resistance values and associated fan speed settings are visible from the outside of the heater boxes.  Fan speeds are stamped into the housing itself. Resistances are on the board next to the terminals. As mentioned above by Mike Self, the spade terminals are the main culprit, so soldering a new connector should fix the problem with broken terminals.

Attached pics of my early (one resistor wire) and later heaters (two resistor wires)

[jimk]

11 hours ago, John76 said:

You're right Jim!  

At least you can read and understand mine.😁

John

I think it was the colors that messed me up.  I only got Ds for grades in electrical classes.

[ray_]

6 minutes ago, jimk said:

I think it was the colors that messed me up.  I only got Ds for grades in electrical classes.

It's not how you're wired.

 

😁😁😁

[Lorin]

1 hour ago, ray_ said:

It's not how you're wired.

 

😁😁😁

As long as he’s not short…

[ray_]

59 minutes ago, Lorin said:

As long as he’s not short…

Well.

 

He has shown a little resistance.

 

😁