Re-building the blower motor resistor

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Mark
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My tercel:: 1984 Automatic, 1981 sedan
Location: Victoria, B.C.

Re-building the blower motor resistor

Post by Mark »

The blower motor resistor failed on the lower speeds a while ago on my wagon. I joined the broken ends of the resistor coils by crimping a connector across them and it worked for a while, but then it failed again. I decided to try and fix it once and for all. I guess I could buy a new one, but with shipping it would cost close to $100. The resistor coils are just nickel-chromium heating element wire so I bought a roll of 20-gauge ni-chrome wire at a local electronics store. 20-gauge seems to be the thickness of the thickest resistor coil. It cost me $18 for way more than I need, but it would probably be cheaper online or in the US. The real blower motor resistor uses 3 different gauges of wire. The thinner gauges are for the higher resistances and allow you to use smaller coils, but they seem to be fragile and in a few cars I've had are always the ones to burn out. I'm cheap and didn't want to buy 3 rolls of different gauge wire so I used the thickest gauge (20) for all three. I'm hoping it will be more durable than the original.
IMG_0761.JPG
I removed my old blower motor resistor and found that it was pretty destroyed. Some of the damage might have happened when I removed it, but the 2 finer-gauge coils were broken in several places.
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I looked online and found that the common resistor values (in ohms) for the 3 coils in several older Toyotas (Camry, pickups) were: 0.4, 0.8 and 1.5.
I checked the internal resistance of my meter by connecting the 2 leads. It was about 0.5-0.6 ohms.:
IMG_0768.JPG
I measured the lengths of ni-chrome wire using the resistance minus the internal resistance of the meter(.5 -.6 ohms). For example, this photo shows the 0.8 ohm length (1.4 ohms - 0.6 ohms = 0.8 ohms):
IMG_0771.JPG
I cut these lengths and made them into coils by wrapping them around a pen:
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I decided to leave the original thickest coil (0.4 ohms) in place since it was the only one that wasn't broken. I used my soldering iron to melt the old solder and remove the old broken coils. I'm not sure what kind of solder was used, but my iron wasn't really hot enough. I had to hold it on the old solder for quite a while before it finally softened and melted. Soldering Ni-Chrome wire is almost impossible so I just inserted the ends of the new wire coils in the flat tabs and bent the end to make them stay in. A concern is making sure that the loops of the coils don't touch each other or they will ground out and reduce the resistance value. The original coils had some kind of ceramic putty on the coils to keep them properly spaced out. I considered using JB Weld epoxy putty, but the stuff I had wasn't rated for the temperatures the coils produce (hundreds of degrees Celsius). I ended up just not putting anything on it and hoping for the best.
IMG_0764.JPG
My other concern was the internal geometry of the vent ducting. I was hoping the red-hot coils didn't come into contact with the plastic ducting and burn my car down. I decided I wasn't building a children's daycare or anything so I could take a risk and I installed the "new" blower motor resistor pretty much as is was in the above picture. It worked fine. All the fan speeds work at what seems to me to be the right speeds. There was a slight hot metal/burning plastic smell for about 10 seconds as I applied current to each coil for the first time, but after that there was no sign that there was a home-made fire hazard in there. So far, I've driven for about 45 minutes in total today and it's working fine.
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dlb
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Re: Re-building the blower motor resistor

Post by dlb »

nice job! that's a great trick, using the pen to wind the wire.

i wonder if the old, hard to liquefy solder is special high temp stuff so it resists melting when the coils are heated during use. when i've repaired these things, i've avoided doing any soldering because i figured it would just melt off and fall apart. the regular stuff must be fine though if your repair is still working.
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Mark
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My tercel:: 1984 Automatic, 1981 sedan
Location: Victoria, B.C.

Re: Re-building the blower motor resistor

Post by Mark »

dlb wrote:nice job! that's a great trick, using the pen to wind the wire.

i wonder if the old, hard to liquefy solder is special high temp stuff so it resists melting when the coils are heated during use. when i've repaired these things, i've avoided doing any soldering because i figured it would just melt off and fall apart. the regular stuff must be fine though if your repair is still working.
I didn't use any new solder to hold the coils in place. I agree that the high temps in the coils would probably melt regular electronics solder. The holes in the flat metal tabs are pretty small and semi-clogged with old solder so I had to force the ends of the coil wires in them. They are now held in there pretty tight (especially since I bent the ends of the wires after shoving them in the holes). Some of the original melted solder probably re-solidified around the wires in the holes as well so I'm not worried about the wires coming out.
I've heard that it's very difficult to solder ni-chrome wire anyway. During this job I tried to "silver" the ends of the wires by dipping them in flux paste and then burning it off with the tip of the iron with a drop of regular melted solder. Usually this bonds a thin coating of solder to the wire and makes it easier to stick when soldering it to something. This time, the solder refused to stick to the wires. I've never seen that before. It always works great with copper wire.
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