The fire box is lighting but the furnace fan doesn't come on. Where
is the temp relay? I've got a York Stellar Plus, Model P1UDD12N09501A
with a Honeywell Chronotherm 3 stat.
I assume the whole circuit is in the furnace itself BUT it could be in
the stat as well. I know I can turn the furnace fan hard on at the
thermostat. Maybe the York return a firebox temperature signal to the
The blower is controlled from the furnace, not the thermostat, when the
thermostat is set in the "auto" position for the fan. It either
controlled by a mechanical bi-metal thermostatic switch or by time delay
from a circuit board. York residential equipment is not all that common
in my area, so from the model I couldn't tell you off the top of my head
which yours is likely to have. How old is the furnace?
On Jan 27, 9:14 pm, firstname.lastname@example.org (Lp1331 1p1331) wrote:
20 years old. I've been trying to find a parts diagram without any
luck. I suppose they don't really want you mucking about in there.
But its got to be a big old industrial part. If it's a time delay on
pwb, then, damn, $$$$$ I suppose.
When you replace a fan/limit switch, be SURE to read the instructions,
especially the part about breaking out the little jumper if it is a four
wire hookup as opposed to three BTDT-caused the smoke to leak out of
most of the 24 volt components.
I don't know about 20 YO furnaces since I went from a 40-plus YO to a
new furnace 5 years ago, so I'll just ask this question:
Did they still use the in-plenum limit-switches 20 years ago? You
know, the probe that hangs out in the plenum and turns the fan on and
off based on the air temp in the plenum?
I replaced the fan-limit switch twice in 15 years on my old furnace. A
couple of sheet metal screws, a few wire nuts and about a half hour's
On Thu, 28 Jan 2010 11:39:14 -0500, "Existential Angst"
Called a "differential". Fan/limit switch can be set to turn on at
whatever temp lets say 170F, and off at any temp let's say 100F.
If you wish a little warmer air on the off cycle increase to 110F.
Closed combustion He furnaces could be controlled by a timer since the
heat exchanger is in a more controlled environment. Traditional
open/forced combustion air furnaces not so controlled so it's better
to use a fan/limit switch which probes the temp right above the heat
exchanger on the inside.,
The new furnace is an HE unit, so I can't (don't know how to) adjust
the "timer" to have the blower come on or go off at a different time,
nor do I want to.
I assume the manufacturer got it right and I have no desire to
override their wishes. ;-)
The "mechanical" fan/limit switch were much easier for the user to
I have seen furnace without blowers. It was totally
inefficient, and the gas bill was horrendus. But, I'm
guessing it would work with out electric.
There is some gravity circulation, if the furnace is below
the heated area.
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