Thanks for the advice Art. I'm going to install it with the factory
defaults and run the furnace through a few cycles. Basically, the blower
should kick in a minute or two after the furnace starts the heating process,
and should kick out a minute or two after the flames go out. If there's not
an uncomfortable cold-ish draft before and after the cycle, then we're in
the ball park. Sound about right?



"Art Todesco" wrote in message
.. .
There is NO reason to get an answer as you did on a forum like this!
This is a Q&A discussion board and that's what you asked and here's
my personal experiences.

The numbers you quoted, "out of the box" are probably fine. Usually
you can't adjust the upper limit .... is that correct on your unit? On my
furnace, the limit switch and the fan switch are 2 physical units. As for
the
on/off temperature, you can adjust it up or down. If you go down, you
will
get more heat out of each furnace cycle, however, at the risk of feeling a
cold draft from the now cooling down heat exchanger. Even 90 degree
air moving can feel cold. My original non adjustable switch in the
furnace
was supposed to be something like 95/135, however, it, and a new
replacement
unit from the factory, never even got close to those numbers. I was more
like 120/155. I then put in an adjustable unit and it works very well. I
adjusted it to allow the fan to run as as low a temperature as possible
and
still not feel too drafty. I think the turn off temp is now something
like 85
degrees. BTW, I asked a rep from the furnace company about my experiences
and he said that he had done the same thing on many units. I think the
manufacturer either had a bad batch of fan switches or the placement on
the plenum was such that it didn't truly represent the temp of the air
flowing
out of the unit. The later was the more probable. I hope this helps.

Jay Luke wrote:
Since I bought the house three years ago, the furnace has always operated
as follows:

- kicks in and blows heat for 30-45 seconds
- fan stops for 10-15 seconds
- repeats this cycle for 30 to 40 minutes, then the fan and the
heating stop
- 60 to 90 minutes later, starts all over

When I had my furnace vents professionaly cleaned the other day, I asked
the technician what his thoughts were, and he stated that this behaviour
is due to a faulty limit switch on the furnace. He quoted a price of
$300 plus tax to install a new one.

After researching online and verifying for myself that this was rapid
cycling, I went down to the local hardware store and found a new
replacement limiter switch for $40, so I purchased it. Installing should
be straightforward since the existing switch is exposed and already
wired, so I just need to set the start/stop limits on the switch.

How are the off/on temperature settings determined? The default settings
on the switch (out-of-box) a
Off: 95
On: 135
Limit 210

I can't refer to the current settings on the existing switch because the
tech had moved them around before leaving.

Anyone have any knowledge or advice on this?

Cheers in advance - jay