We just moved to a new home with a Carrier 58PAV up-flow gas furnace.
The furnace checked out fine before we moved in, so I'm not sure if the
way that it's currently operating is normal (and it works in a way I
don't expect), or if something is wrong:
Say the temperature in my house is 68 degrees, and the thermostat is
set to HEAT at 71 degrees. Well, the furnace stats circulating the
air (that is, air is moving through the system and into the house so
the blower fan turns on), however it's just the ambient temperature
(whatever temp it is in my garage and ducts - but not hot/warm). So,
effectively I have this cool breeze blowing through my home! If I set
my thermostat up to 90 degrees, then the burners click on and start
heating the air. I'm not sure why the 'call for heat' isn't heating
for low differences in temperature..?
am I totally nuts? Thanks in advance for your help...!
This is the way some/many of the newer
units work. I hate it. It's dumb..
My 18 year old 90+% recouperative unit
doesn't turn the blower on
until the plenum gets hot. AND, even
then, for a second or two, you
feel the cold draft.
So... This is 'normal' operation? I have to set the thermostat up to
90+ degrees to get any warmth? Grrr..! The other night we had the
thermostat set to 71 degrees, and the outdoor temp got to the mid to
low 60's - I'm fairly certain that the system just circulated the air
throughout the night (that is, it didn't warm the air, just that cool
breeze all night). However when I woke up (shivering - indoor temp
was below 70 degrees) and pushed it up to 90+, the house got warm
pretty quick...(then, of course, I turned the system off...)
Is there something I can set/change to change this? As I mentioned
before, the furnace is a Carrier 58PAV up-flow. Also, my thermostat
is made by Totaline - although I'm not sure of the type, it seems
pretty low end...
Mine works that way. I'm sure you know that it's inevitable that
you'll feel cold air at first because that's the air in the ducts.
By coincidence, today I took apart the control unit for my furnace.
23 years ago it seemed pretty complicated somehow, but today I noted
it had only 2 resistors, a capacitor, and two simple 3-wire
transistors, plus a power relay, and a cutout relay that functions
when there is no flame, for example. It's simple. For example, the
cutout relay only has 4 wires. I think the power relay also has only
So how *does* it manage to delay the fan from coming on until the
plenum is hot, and delay it from turning off until the plenum is cool?
Maybe those two things, related, are the only things it does. I guess
it has enough parts to do that.
The small number of parts makes it all the more annoying that they
wanted 200 dollars for a replacement 23 years ago. Of course that one
would have also had the 110 to 24 volt transformer, but when I groaned
at the price, they sold me the transformer only for 10 or 20 dollars.
That hasn't needed repair since. (Remember that weekend, Paul?)
Last night around 2:30 I thought my carbon monoxide detector went off.
I woke up and was too groggy to remember if the green light was
supposed to be on, and my eyes couldn't tell if the red led segments
lighting up were a, b, c, a, b, c, which is normal, or a, c, a, c, a,
c which isn't. So I turned off the furnace. Gradually I reallized
there was no CO, the alarm didn't say there was, and the noise was
from the upstairs wireless doorbell which sqawks loudly, twice, after
every power failure. (I had noticed a vcr and a digital clocks that
were flashing 12.
The typical furnace has a temperature
sensor on the plenum. when it
gets hot, it starts the fan, when cool,
it stops. Some of the sensors are
actually dual; one to run the fan and
one as an over-temperature safety ....
some are separate. Some are adjustable,
most are not. Mine originally
(non-adjustable) waited too long (too
high temp) to turn on and waited
too long to shut off (cold air blowing).
I call the company, they replaced
it; the new one was worse than the
original. I finally bought a new,
adjustable one; set it where I wanted;
works perfectly for the last 18
The older furnaces had a temperature sensor that extended into the
heat exchanger. Called a fan limit switch. One totally hot summer day
I had the furnace blower kick on. Wasn't sure what was going on, until
it finally occured to me the furnace was hot enough it thought there
was fire in the firebox. Ah, well.
Christopher A. Young
You can\'t shout down a troll.
No it's not normal. When a house is inspected usually only operation
is checked. Not quality of operation. Get a HVAC tech to check it
out. Your t-statmay be bad or another component isnt working
On 19 Nov 2006 08:48:03 -0800, firstname.lastname@example.org wrote:
Is the thermostat digital or analog? If it is analog then the heat
anticipator is defective. Open the furnace up and remove the red and
white wire from where ever they connect. Take a piece of wire and
connect it to the red and white post/screw that you just took the
wires off of. Does it fire up? if so then your thermostat is
The furnace has a two stage gas valve, the low stage uses less gas thus
produces less temperature rise at the registers. When you set the thermostat
to 90 the second stage comes on thus increasing gas usage and resulting is
warmer temperature from the registers.
The fan speed may be adjusted too high for the low stage burn or your
expectation of the delivery temperature doesn't allow for the low stage
burn. If you measure the temperature of the supply air I think you'll find
it is warm ay low stage burn but not hot as it will be at high stage burn.
okay... sorry it took me so long to get this reply out. Thanks to
everyone who contributed to the explanations! I just have to say that
I'm really glad that manuals exist and are easily downloadable on the
internet! The problem was indeed in the thermostat. It turns out
some of the settings in the thermostat (Totaline P474-0100) were not
right (and the previous owners of the house must have just suffered
with it). The settings in question were the 'electric heater fan'
option, which was mis-set to ON. This was causing the blower in the
[gas] furnace to blow cool air through the house. The other setting
was the 'dT' setting (or the 'wiggle factor' setting) which gives a
'buffer' to the temperature set point. It was set to 5 degrees
(wow!), I set it to 1 degree. This may make more sense if I explain
how the thermostat works... For this thermostat, the 'call for heat'
is set up in two stages:
(say my house is at 66 degrees and the temp I've set the thermostat to
turn the heat on at is 71 degrees)
stage 1) when the indoor temp reaches the setpoint (71 degrees) then
'stage 1' has been reached. A red LED turns on on the thermostat
indicating that it's reached the set point, and if the 'electric heater
fan' option is set to ON, the blower is turned on.
stage 2) if the temperature gets to the setpoint - wiggle factor - 2
more degrees then the furnace is told to turn on.
So, what I was getting was the blower turning on at 71 degrees because
the thermostat thought my furnace was electric. This horrible breeze
would circulate through the house until the thermostat reached 64
degrees (71 degrees - 5 degrees of wiggle - 2 degrees), but since the
house was sitting at 68, the thermostat would never turn on the
burners! The result for me was exactly what I was experiencing. It
appeared that for small differences in temperature (between the heat
setpoint and the house temperature) I was just getting this cool
breeze, but if I boosted the heat setpoint up (say to 90) then the
stage 2 criteria were satisfied and the thermostat would send an
appropriate 'call for heat' to the furnace...
On top of this, the thermostat was measuring the wrong temp to begin
with, so I went ahead and recalibrated the temperature sensor... What a
So now my furnace turns on at exactly 3 degrees below the heat set
point since I can't set the 'wiggle factor' to 0 and 2 extra degrees
are hardcoded into the thermostat, but I no longer get the cool breeze.
This is MUCH more acceptable! Tthe previous owners must have always
just compensated for this problem! I'm really glad that the manuals
were online! Thanks again for everyone's suggestions!
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.