In case you didn’t already know, some time ago Dometic started introducing a new line of thermostats. Where you normally think of a thermostat as either a mercury bulb (old technology) or a bi-metal spring (even older technology) you now think of a thermostat like a Serial Device. Really! That’s the best way I can remember it, anyway.
If you’re old enough to know what large SCSI Hard drives were… you’ll catch on here.
If not… well, I’ll try to give you an explanation that ties about a jillion years of technology into one easy paragraph. (Ok, maybe not a jillion years, or one paragraph…)
Back in the day, you could add external hard drives to your computer system through the large pinned ports on the back. You could plug one new drive into each port. If you had one port, you’d get one hard drive. If you had two ports, you could add two drives. But what if you wanted – no, needed – to add 3 or 4 or 5 of these gret big 9 gigabytes harddrives?
The way we do it now is via USB. Real simple, you just get a 4-port hub, go to WalMart or where ever, and start buying hard drives, and keep plugging things in. Woohoo. You get a terabyte. You even chain those USB ports together, because theorectically the limit is like, 256 devices deep, right? As long as you’ve got power enough to drive the devices…
What you’re not considering though is what ties all this together (and back to Dometic’s new style thermostats ggg)
Thermostat, Multiple Zone LCD Comfort Control Center 2 (black shown)
It’s called TERMINATION.
Not like getting fired, or like some Ahnuld Schvartzen Egger movie… like putting and END to something.
Those old SCSI drives (Small Computer System Interface) could be daisy chained from one item to the next, or run one at a time… stacked up several deep on each line… but they had to be TERMINATED properly. As in, the last one in line had to be marked as the last one in line. No matter how many lines you had, each line had to know what was the last device at the end of the line. (Or, like kids on a playground. Stand them all in a straight line. Hand the first kid a pail of water, and tell them to pass the bucket to the end of the line and back. What if the last kid in line didn’t know he was indeed the last kid in line? What if he wasn’t properly “TerMiNateD”? would he just stand and hold the pail forever, or just hold it out and drop it , or what? )
USB devices, believe it or not, do something similar. And so do the new Dometic thermostats.
The new thermostats don’t have bimetal springs, mercury bulbs, or a lot of things you might expect to find inside a thermostat… and they DON’T directly switch the heat and air on and off!
These new Dometic thermostats, both the Single-Zone and the Multi-Zone versions, Terminate a line coming out from what used to be a relay board in the belly of your rooftop air conditioner. Only now, instead of a relay board with high-current 4PDT relays and silver contacts, the heavy lifting is done with semiconductors and a different switching technique. Your now Dometic thermostat, to me, fits the functional definition of a “serial device” just fine.
If you open up the thermostat and look, there’s no bi-metal spring, no mercury bulb, nothing in there you can twiddle or fiddle with to make it “do” anything. All that is being handled at the new control board. The thermostat is now functioning as a sensor, out on the end of a line, terminating it and feeding the conditions back up to the processor in the air conditioner (or heat pump, etc.)
Anyway, the gist of this that if you are using the old thermostat, and the relays that go with it, there’s a very good possibility when they finally poop out you’ll be installing the new SZ or Multiple zone LCD thermostat, and board, as a kit. and now you can see why.