Hi all - Need some experienced HVAC advice with a 90's mercury thermostat in our apartment we just moved into.

Mrs. says that the AC runs for what seems like a longgggg time between cycles.

I have taken the cover off and there is a rotary control labeled 'Longer Cycles' and a circular arrow. I can guess if I adjust to reduce the arrow, it will shorten the AC cycle, but what are the units of measure around the edge? Minutes? Degrees F?

Thanks, hoping someone has seen one of these adjustment disks before?

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Take your time, fast. J.Hughes

Works like every bi-metallic coil mecury switch thermostat made since , , , long ago. When they get old , they don't always move as fast as they should. (like most of us!)

Ya could always get a programmable thermostat and set it however hot/cold and whenever off/on ya like. They aren't very expensive. Probably $50-65.

Simple hook up and when ya move out take it off and put that antique back on the wall.

Hysteresis

Ok, thanks guys. Figures.

I'll have to check and see what restrictions the apt has on electronic thermostats before I install it. We just moved in Oct and I've been on the road for work last few weeks.

Home Depot, Honeywell pro series tstat...

That little wire with wiper is actually a pre heater to cycle the furnace on sooner/later. It doesn't have anything to do with cycle length. If your furnace seems to stay on too long, your furnace isn't getting up to temp. A clogged filter could be the cause, or something not working in your heating element.
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Boxers or briefs? At my age, Depends.

Haven't seen one of those in years. As a kid we used to collect them and bust open the glass tube and dump the Mercury in a jar. Collected a whole bunch of the stuff...even played with it at school. Looks real neat when dumped on the linoleum floor...went everywhere!

And now they tell me that stuff will kill you.............

You live in a apartment, call maintenance they will fix it if you don't want to replace it yourself. If you want it replaced wiggle the wire carefully at the vile until the wire breaks, to be sure they replace it. If the vile breaks then call OSHA "Mercury Releases and Spills". Mercury Releases and Spills | Mercury | US EPA

If they don't replace it then tell them if the vile breaks you expect them to follow the EPA guide lines for clean up to the letter, would cost more then replacing it.




We played with them also before they thought to tell everyone it was dangerous. Kind of like asbestoses , AAMOF still got one of those quick "silver switch's" in the ol'tool box. I'm still alive but maybe that's why I'm a ol'grouch. No that's because I'm old.

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Psalm 23:4

These devices are called heat anticipators, and their function is to match the t-stat to the appliance. Your furnace's control circuit draws a small amount of power when it's on, and you set the slide switch to that amount to optimize the two devices. If you have access to a clamp-on ammeter, you can determine what this amperage is very easily. At the furnace, find the white wire from the T-stat to the furnace and read the current flow when everything's running. Probably around .3 amps usually.

Bah! you and your facts!!!

Llando; a question: Are we talking heat, or AC cycle?
I am with the thought that the bimetallic strip might be slow to expand/ contract from age. But in reality, it's not a problem, because it still cycles and you can anticipate this and adjust for it manually a little.
I also firmly agree about changing the filter. Air flow can be a real game changer, as just a few less CFM can lead to higher flue temps on a heat cycle. This can lead to the hi temp limit switch cutting out. It can also lend itself to a system which does not move enough warm air to move the needle.
It can lead to colder coil temps and icing over the coil on an AC cycle. If the coil ices over, then you will get less CFM of air flow, and it is a self-fulfilling prophecy as to more ice, and less air flow. Also, this can make it so the AC will run a longer cycle, because regardless how well the coil is cooling, the air flow is not sufficient to move the needle in the T-stat, meaning a longer run time.

The T-stat is not an issue; do not change it. No need to.

To run at peak efficiency you HVAC plant needs to be sized near max capacity. The longer the system runs the more efficient it is. A short cycle is more costly than a long one but the reality is we are talking only 2-3% maximum difference past the first 45 seconds. Tell your wife the longer cycle is saving you money.

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Front sight and squeeze

Lol. When I was a kid one of my buddy's dad's gave him a 3 foot long lead bar to play with. That thing was cool as hell. You could bend it and twist it all different ways. Bare hands of course!

Filter is clean, within 30 days; yes, this is AC. We live in Tampa.

We are not familiar with this "Furnace" device ya'll talking about.

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Take your time, fast. J.Hughes

It's like a couch, but it makes heat. The real name is 'Furnaceture'.......... try to get a friend to sit on one!!

Like one said, the adjustment is the heat anticipator.
To test the operation on cooling, it should be cycling to
maintain the temp you select, plus or minus a degree or two.
You can use the thermometer on the T-stat to test, or if you
want to test the whole thing, use an accurate thermometer in
the same location as the t-stat. Only if it were showing a large
error, would it be considered bad.
It's quite possible your system is slightly undersized and really
needs to run that long to maintain the set temp.
Which like one says, can actually be good in some ways.
A system that runs like that will be taking more moisture out of
the air than an oversized system that doesn't run very long to
maintain the temp. The oversized system will often make for a
damp feeling house or apartment.