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Finally got my 79 rx7 registered and on the road. A 29-month adventure. I am supremely thankful of the help the people on this forum have been. Thank you.
Love teaching myself manual, the fact that it's on the road because of me, the sound it makes. It's fantastic.
Unfortunately, it's August in Texas. I would love to have AC. I've done a lot of research on charging the system myself and everything I'll need. Went to turn on the blower motor, didn't turn on, and blew a fuse. Strange, the blower motor had worked for the last 29 months, whenever I felt like turning it on. Get everything torn apart and turns out the resistor has broken through. Nobody sells these. I found ONE on eBay. $40 for a very fragile, 40-year-old, used part. Eh
I had a thought that since these are just simple resistors to output different fan speeds. Could I not just solder in some modern resistors of the same or similar resistances? Even though I have no idea what the resistances are...
But likely what you are going to find are resistors that are not meant for the wattage range you are looking to deal with and will burn up real fast. The little ones with the coloured bands will NOT work here.
I don't know what that blower motor draws for amperage off hand but lets say it draws 5 amps at 14v, which is 70 watts. You would need big resistors like you might find here,
What I would suggest, if you don't want to find a used one (and I bet they will be easy to find if you make a wtb thread, I have a spare one here myself), is buy any new blower motor resistor with wound wire, such as this one from an 86 626. https://www.rockauto.com/en/moreinfo...89740&jsn=1565 Then cut the wound wires off (the longest wire representing the slowest blower speed) and soldering it in place of your failed ones.
You can try winding your own resistors from kanthal wire like this
but you will have to experiment with the correct length/gauge to get the resistance right. A complete blower resistor you can rob instead like I linked above is about 30 bucks.
You can also update to a more modern style blower resistor which makes a lot less heat, something you might find in a 2008 ford escape or similar. It will be up to you to make any of these things fit.
The two things I'm most considering is robbing one from an 86 626 like you mentioned or posting a WTB. I'd imagine people would want around 30-40 dollars to sell me one.
They're really quite fragile and the hardening material to keep the windings from moving has likely fallen off. So robbing new ones from the 626 or similar would probably be the most likely option to prevent me from having to revisit this.
I'm in a similar state, reinstalling my AC and have found that the low speed no longer works. I've been eyeing up some modern new Ford blower motor resistor packs as well for a couple of reasons; Ford and Mazda used to be real close, so shared a lot of parts and I have to bet the blower motors are very similar.
the Rx8 resistor is really basic looking, blower as well. also the miata... actually the 90-97 miata blower might got right into an 81-83 Rx7, its supposedly the same HVAC system
the Rx8 resistor is really basic looking, blower as well. also the miata... actually the 90-97 miata blower might got right into an 81-83 Rx7, its supposedly the same HVAC system
Is the resistor pack different for SAs? WOuld the miata one work as a replacement? I need to start digging.
The resistor pack from an 86 Mazda 626, very similar to the one out of my SA Rx7. Same "wound-coil" resistor style.
The 90-97 Miata Resistor pack:
I'm sure you could make it work if you really wanted to, but I'd be worried about it not being 1:1 replacement with the SA version. (Blower speeds, etc)
Edit: Actually, looking at the wiring for the Miata pack, the wire colors look the same as the factory SA wires. Not sure if the locations on the plugs are the same
The two-pin plug looks like it would plug right into the SA Blower motor. The four-pin looks like it would plug right into the SA switch plug, as well. IF the wires are long enough. I don't believe the SA has a single-pin plug, though. Not sure what that does. Looks like it's just a solid blue wire, which doesn't exist on my SA.
Blue wire according to the wiring diagram is 12v in to the motor.
It wouldn't be exactly plug and play. .
If it's a 4 speed 12v blower motor, you can pretty much guarantee your blower speeds will be similar regardless of what vehicle you get your blower resistor out of.
7aull, that second link is the exact one I found. That first link is the control module that mounts on the inner fender, driver-side.
I'm going with an 86 626 blower resistor. Going to rob the resistors and solder them onto the 79 resistor pack. That's the plan, at least.
Only got 3 fan speeds in my SA. No solid blue wire either. Looks like power is provided to the motor via a blue wire with a black stripe. The 626 resistor has 4 coils on it. Looks like I'll take the resistors that output the fastest and slowest speed, and then just figure out which of the last two I feel fit the medium speed better.
7aull, that second link is the exact one I found. That first link is the control module that mounts on the inner fender, driver-side.
I'm going with an 86 626 blower resistor. Going to rob the resistors and solder them onto the 79 resistor pack. That's the plan, at least.
Only got 3 fan speeds in my SA. No solid blue wire either. Looks like power is provided to the motor via a blue wire with a black stripe. The 626 resistor has 4 coils on it. Looks like I'll take the resistors that output the fastest and slowest speed, and then just figure out which of the last two I feel fit the medium speed better.
I hadn't realized some of the images were so off-looking until I sat down to write this.
This wasn't quite as easy as removing the old resistors and slapping in the new ones. Primarily, the difficulty I had was that the 626 resistors weren't designed to fit where the Rx-7 resistor assembly is supposed to fit. Surprise, surprise. The resistors for the rx7 are thinner gauge wire than the 626. This is only really an issue for the spade terminal labeled H2. There are 3 wires soldered to that pin. The 626 resistors will NOT all fit in the slot for that tab. I just soldered the last wire outside of the slot for the wires. The only other difficulty I had was my soldering iron is pretty old and definitely made the job take a lot longer than it needed to.
Another thing to note is that the low-speed output is the TOTAL resistance of all of the resistors. Like-wise, the medium-speed output is the medium and high resistance added together.
I also have no idea what the purpose of the two pins at the bottom of the image below are for on the Rx7 resistor assembly. My system just had a loop that goes from one terminal to the other. Not standard, for sure. I guess to bypass the high-speed resistor so the motor blows full blast when set to high and faster all-round at lower speeds since the high speed resistor is bypassed? Not sure. I don't recall if having it installed or not changed the output speeds. If I notice something seems off when I fully reinstall the system tomorrow without the loop, I will let you know.
A side-by-side of the two resistor packs.
I've got the resistors labeled from 1 to 4. 1 being the lowest resistance and 4 being the highest. The LOWEST resistance outputs the FASTEST fan speeds. I used 1,3, and 4. As far as I understand, using 2 instead of 3 for the medium speed would make both the medium speed faster and the low fan speed a little faster as well, since the lowest speed is the total resistance. Resistor 1 will replace the shortest and thickest resistor on the rx7 assembly. Resistor 4 will replace the longest and thinnest resistor on the rx7 assembly. Cut them off as low as you can, bend them so they line up with the tabs on the SA pack to make soldering them in a little easier.
One final note, by the time I had finished up, most of the green stuff to keep the wound resistors from moving had fallen off. I used some Plasticweld epoxy to make some new ones. Seemed to work fine. Though, with how much thicker the wire is for the new resistors, I wouldn't be too worried about them not having any at all.
I tested the whole system before swapping out the resistors (when it worked) and there was no significant difference in fan speeds after installing the new resistors, so that's nice.
Wow. This IS a deep dive. Lost me way back on the Tech, but kudos for the effort. May you be rewarded well for the effort...
I know I have seen these damn things FS on ebay and will post links if I find them. Carry on!
I left it installed since it was there when I removed the system.
Hmmm. I plugged the blower in, set it on the floor of the car, and tested it before bolting it back in all the way and the resistors didn't get very hot. Now that I think about it, when I was testing them in the shop, I left that little loop off and they would get hot enough they were difficult to hold. No idea how the loop does that but there you go.
@Ta-Aikah I can't really follow the path from the pictures but I'd imagine either the extra length of wire either adds resistance or hell maybe provides an alternate path for the current to travel.. Basically the resistors, some or all, are installed in parallel with the jumper installed. Why this needed to be installed stateside during the AC install we'll likely never know. Ooo maybe installs without AC their are less speeds or the current is controlled from the MVAC control box. Possibly the air blowing over the resistors help with the heat in a none AC install?
It definitely gives the current an easier path, but the way it's set up it looks like it gives a direct path to skip the resistor entirely for the high setting, yet the loop being on or off has no effect on the speeds.
Wouldn't adding resistance make them hotter? Maybe it lowers the total resistance, so they keep cooler. You would think changing the resistance would change the fan speeds though...
The blower fan definitely helps with the heat with or without AC, but they were getting hot enough during testing for the fan to not make a difference.
See the wiring diagram. All that loop does is short the high speed so it runs faster. With that loop in place on high you will not feel any of the resistors getting hot.
The air conditioning would still work if that loop is not in place, but the blower motor would run slower and the resistor would be putting heat into air discharge.
See the wiring diagram. All that loop does is short the high speed so it runs faster. With that loop in place on high you will not feel any of the resistors getting hot.
The air conditioning would still work if that loop is not in place, but the blower motor would run slower and the resistor would be putting heat into air discharge.
This makes since. Looking at this, they are not in parallel. the resistance is additive based on the desired speed.
So I can't find the 86 626 resistor pack on RA anymore but I did find the 86 323 is still available and looks the same. Will be fixing mine in a similar manor. My low doesn't work because that resistor coil burned through for some reason so its an open circuit for low.
About that loop on the SA install. Mine has it. I read somewhere that when the fan is on high it's to disable the resistors so extra heat is not in the system at least on high. I suspect its a bit of over engineering on Mazda part because the other models we see having similar packs now don't need that loop and instead get a direct feed from a blue wire from somewhere. The 86 323 resistor is identical except for that feature.
08-08-20, 05:40 PM
Blower Motor Resistor Idea
