Re: AC thermostat malfunction


<trader4@xxxxxxxxxxxxx> wrote in message
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On Dec 8, 7:11 am, "RBM" <r...@xxxxxxxxxxx> wrote:
"MiamiCuse" <nmbexc...@xxxxxxxxxxx> wrote in message

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"Oren" <O...@xxxxxxxxx> wrote in message
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On Sun, 7 Dec 2008 18:25:42 -0500, "MiamiCuse" <nmbexc...@xxxxxxxxxxx>
wrote:

I have the old style thermostat on my AC that is giving me some
trouble.
I
have played with it a bit and have isolated the problem to the point I
think
may be someone can tell me if it can be fixed or have to get a new one.

It is the old style with a mercury bulb inside, the manually adjust a
dial
to the desired temperature. There are two switches:

- fan ON or AUTO swicth - I leave it on AUTO
- HEAT OFF COLD switch

Down here in Miami, I pretty much leave the HEAT OFF COLD on COLD. I
set
it
to 72 degrees and that works fine. If it dips below 72 the AC kicks on.

Last two weeks we had a cold front so I turned on the heat, I might use
the
heat once every two year or so, last may be a week here, a week there.

If I set it on HEAT the heat does not kick on no matter how I adjust
the
temperature settings.

I then removed the cover, and adjust the settings left and right and I
can
see the mercury drop rock left and right.

However, if I set the switch from HEAT to OFF, wait 2 seconds, then set
it
back to HEAT, if I then adjust the temperature setting I can see the
mercury
drop moved to one side and when it hits the wire filaments inside a
very
faint spark, and the heat comes on. It stays on until the temperature
is
reached then it goes off. It will stay off from now on unless I turn
the
switch to OFF and back to HEAT, and adjust the temperature then it will
come
on again.

Any ideas what is wrong?

Thanks for any comments.

MC

Replace the T-stat with digital. Save the mercury and poor into
drilled out bullets.

Is it easy to wire in a new thermostat? Do I just pull it off and the
new
one will match up to the existing wiring?

You first have to identify what type of thermostat you have, which you can
do pretty much by identifying the letter terminals that are on its base.
Once you know what you have, you get a new stat with the same or more
lettered terminals that it has. When I replace thermostats, I leave the
existing unit attached to the cable(s), and with power to the
heating/cooling systems off, I cut the cable(s) close to the stat, then
mount the new unit and wire it terminal for terminal by looking at the old
unit



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It's hard to imagine a simple old mercury thermostat behaving the way
that is described. If it turns on and correctly works each time it's
moved from off to heat, but then doesn't work a second time, I can't
conceive of a problem with the thermostat that would make it behave
that way.

I can't either. That's why I suspect whatever heating system its attached to
may be locking out


.

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