Thursday, April 24, 2008

"Lo"? What the !@#$ does that mean?!"

this is the promo shot, not actually my thermostat
One of those standard things I think all homes should have is a smart thermostat. We bought this one shortly after moving in. Though I agonized trying to find a reasonably easy-to-use one that fit the space, I failed. Its sort of junky. Do not buy it.

One thing is that its sort of hard to manually control. There is no real "fan-only" setting, for example. You end up working around the software a lot, to trick it into things.

Lately, its been worse. Its performing uncommanded actions. You set it to manual, click over to the air conditioner (which is still "unplugged" so will not engage) and if you wait a bit you can see it go "nope, you need heat." The little heat-mode icon lights up, and then the wavy lines that mean its making heat light up. Go to the basement, and yup, the heater is on. On a 76° day. One other hint, the temp display has a tendency to say "LO" instead of a number.

So, I finally give up with shorting leads and beating it with a screwdriver, and call the tech support line. Turns out LO means off scale low. The tiny, stupid computer in the thermostat thinks that its freezing cold. But its not, its just a bad temp sensor. Apparently, it feeds signal directly as a resistive signal, and 0° is about 0 volts.

Okay, its not the computer's fault. Its the designers. While its nice it says (cryptically) off-scale low, instead of a falsely low temperature when it gets a zero voltage response, who decided that the thermostat is smarter than the user? I am requesting "cooling" mode, so why switch to heat mode all by itself? Or, how about a spurious data sensor? It seems to disregard the 95% of the time it gets valid temperatures in order to fire some emergency recovery mode if it gets ANY zero-voltage temp gauge readings. This is poor design, making me sweat and wield a screwdriver needlessly.


Deana said...

that gives new meaning to 'the ghost in the machine', eh? crikey, Hoob. Craziness.

shoobe01 said...

Shamelessly copied from RISKS 25.14, another bolted-to-the-wall box fails in a particularly useless manner:

Date: Sun, 27 Apr 2008 19:56:37 -0400
From: "Daniel P.B. Smith"
Subject: False alarm guaranteed after 7 years

Last night I was awakened at 2 a.m. by an alarm beeping every thirty
seconds. A few minutes of stumbling around trying to find the high- pitched,
hard-to-localize sound revealed it to be our Kidde Nighthawk carbon monoxide
detector. Its digital display was reading "Err." It was not showing a low
battery condition, but just to be sure, I replaced the batteries, to no
avail. I then took the unit down and looked for directions on the back. A
sticker on the back said "UNIT ERROR: Intermittent audible alarm every 30
seconds. Refer to User's Guide for details."

Was there any cause for concern? Well, probably not, since this obviously
was not the ALARM CONDITION, signaled by a different pattern of beeps. On
the other hand, it is human nature to ignore real warnings through wishful
thinking (radar echoes at Pearl Harbor in 1941 must be incoming __American_
planes). I didn't want to make that mistake, so I decided I should at least
check the User's Guide... but could I find it? Not likely. I was wide awake
by now, so I figured I might as well try to download it from the
manufacturer's website. Among other things, if I had enough mental clarity
to do this it would prove to me that I wasn't anoxic. I found it, downloaded
it, and in the "unit malfunction" section I learned that

"Seven years after initial power up, this unit will 'chirp' every thirty
seconds to indicate that it is time to replace the alarm. The unit will not
detect CO in this condition."

Since the sticker on the back showed it was assembled in November, 2000, I
figured that the mystery was solved, took the batteries out, went back to
sleep, and replaced the unit the next day.

Apart from this planned obsolescence being "very convenient," as the Church
Lady used to say, the RISK is of confusing users just in a situation where
things should be as clear and unambiguous as possible.

Was there really not enough room on the back of the device itself to note
that it would beep and show "Err" seven years after installation? And was it
really impossible to program a different message than "Err" for the
seven-year expiration condition?

At least mine didn't wake me up by beeping. Original link:

Wunderkind said...

does that mean?!" this is the promo shot, not actually my thermostat ...

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