From the last log, it started with a burnt heater-fan speed switch, yeah, it was gnarly.

The housing around the contacts/terminals crumbled out while exploring the damage.

I had bought that [the third] two winters ago, a cheap push-pull SPST on/off 20A switch, rather than the 4-position rotary-switch designed for the job. I wired it up so Off was the lowest speed-setting, which places three resistors in series with the motor and ground. On, then, was the highest speed, bypassing those resistors, wiring the motor straight to ground.

I almost, this time, bought a slightly higher-quality SPDT toggle-switch, 35A this time, which'd'a given three speeds... but, it would still be switching directly between essentially-off [low-speed] and full-speed... inductive arcing, much? 

So I started thinking. Per chance, a few logs back i'd done some research on switch-contact-ratings, for another reason entirely, and one of the resounding factors in such ratings is *inductive loads*... like motors, which can cause arcing during switching that'll destroy the contacts' conductivity... so much a concern that, say, a 5A 120VAC switch is downrated to 5A at 14VDC (fourteen!). It's kinda a big concern! 

Now, I dun have with me an ammeter capable of measuring the current-draw of my blower-motor... its fuse is 50A, and it just destroyed a 20A switch. And that after what looked to be a slightly-higher-quality-but-similar switch a couple years back, and *that* was a replacement for [I assume] the original factory-installed switch. Yesterday's purchase is *at least* the fourth.

So, more thinking... yahknow, they could reduce quite a bit of contact arcing, in this shorted-series-resistor arrangement, by using make-before-break switching... and that'd be comparatively trivial to do in... A Rotary Switch. [Like the original].

So, I coughed up the extra $17 for an aftermarket switch intended to replace the switch designed for the task, on a whim that said design mighta considered make-before-break, the intended current-draw, and likely more I hadn't'a thoughta... *and* on the whim that said aftermarketers followed-suit...

Well, sure-enough they did. It's actually more elegantly-simple, yet more fully-functional, than make-before-break; because we have tap-points at each resistor, they merely short the resistors that would otherwise be bypassed to ground. 

So, like, the lowest speed-setting no contacts are shorted, all the resistors are in series to ground. The next speed-setting shorts the first tap-point to ground through the switch... But, of course, the resistors are near the motor *and* grounded there, and the switch and its ground are several feet away, so it's more like a small resistance in parallel to that first [small-resistance] resistor. Now the higher current through the motor has two paths, reducing the strain on the switch-contacts [and wires].

Then the same for the next speed-setting, now there are three paths for the even higher current.

It's a strange blend of cheap, lazy, and yet highly-effective in a way that regular "high quality" general-purpose switch-designs would be hard-pressed to mimic. 

Take it a step further, the actual process of physically engaging contacts can wear them [and the bearing-surfaces, etc.] out, especially considering the surface-area necessary for such loads, but in this design each contact only makes/breaks once over the entire range!

Definitely worth the extra $17 for the learning-experience, alone. I can't vouch for the quality of this particular implementation, yet... Before I had the make-before-break idea, I was pretty turned-off at its being housed in plastic, being that overheated plastic was the problem at least twice before... OTOH, with the potential for much-larger contact-area, and the seeming solid single piece of formed metal all the way from the connectors to the wiper [rather'n, say, a connector riveted to the contacts], there's not nearly as much room for resistance to create heat in the first place. So, I guess we'll see.

---

And some updates on "Other while-dash-open ideas include" [from the last log]:

* 12V banana plugs, ferchrissakes.

* [Maybe 5V and-or built-in USB? + switch!]

* Heater only does recirc with AC running, by stupid design. Add AC cut-off switch

-- Actually, I fought this all day... eventually running an indicator light off the A/C compressor's clutch, and seeing nary a blink. Then hours of research trying to find a phantom relay and phantom schematics... turns out, the User's Manual says, A/C is *enabled* in most modes [including recirc and defrost], but only comes on when the ambient temperature is above "around" 43deg F... [sheesh, was it *that* cold all day?!] And, I *finally* found a schematic, which clearly shows the circuit, *including* the clutch, which is, actually, powered through the dash-switch, not a relay from some unknown pin on the computer... the other schematics showed only the switch signal [via intermediate sensors/cut-offs] going to the computer, no clutch to be found. Apparently the computer uses knowledge of the clutch's engagement [rather than knowledge of the switch/sensor-state] to adjust idle-speed, etc. [rather than turn on/off the clutch]. The new schematic actually explains this, *and* shows the clutch. Sheesh. After *hours* of deduction and research.

--Days later, surely it's been hotter than 43deg a few times... so far I've only seen the indicator-light blink briefly when I start the engine while recirc is on. For this season, that's great. Means I'm not cooling the warm cabin air [and using extra gas to do-so] before reheating it. Maximal heating. But, by-design, that method is also supposed to be used with defrost; cooling the air first causes condensation, which drips outside. It's a dehumidifier, by design. So, I haven't really needed dehumidification, so far, but it would seem it's not an option in the current state of things [which is weird, because just a week before installing the A/C clutch indicator, it was so dry I was getting zapped!]. Seems ridiculous to be even thinking about A/C these days, nevermind never having had it prior, nor expecting I ever would have it... but, apparently it can be something to consider, even in winter. So, I guess, there's something not-quite-right with my A/C system, but it's *mostly* favorable for now.

* Aux Lighter-outlet melted-to-short. replace!

-- Looked into this a bit, too. Shitty SHITTY design. I'm sorry. 20A has to go through a rounded-head held in place with a spring that tries to push the entire plug out, and they mount that contact on meltable plastic?! No, it gets worse. That contact is riveted to the connector, that rivet compresses two housings which has the ground-shell compressed [via meltable insulator, and a positive rivet] to the ground-connector. Positive contact melts through insulator, [luckily] shorts to ground-shell [blowing fuse], and the whole system basically self-destructs. If it went just a tiny bit differently, positive and ground wires would be exposed through various pieces of dangling metal and likely fall on any number of electronics behind the dash. Two bolts and a PCB-material washer should['ve] fix[ed]` the problem permanently.

* Surely more... blanking.

* Oh, stereo power-source selector-switch!

* Also might look into cleaning duct-work.

-- It's a start, anyhow!

* Still... surely more...?