Hi i found a similar problem i have in this group and i like to get great
advises from here..
I have Bryant Plus 90t Gas Furnace, Model # 352AAV036080, Series A,
Manufacture Date 2007,
My quistion is "HOW TO FIX BLOWER FAN NOT TURNING OFF"
HERE ARE THE DETAILS:
my thermostat set to 20'C, the FAN was set to "AUTO", and HEAT "ON".
we where out to grocery store and when we came back we feel so hot inside the
house. i check the thermostat it was set to 20'C and the temperature inside was
25'C and the furnace keep running...
I set the thermostat to heat OFF and the furnace stop. but i notice the fan
still running all the time..
I try to set fan ON or AUTO its running all the time.
So I call the Gas Emergency Service in the city and they check... . The service
guy said my furnace has no problem..and he said thermostat has a problem.... he
told me to call a sevice contactor to replace the thermostat.. and he walked
away because its just a free service of the city..
So I didn't call a service contactor. i did go to home depot and buy a new
thermostat, i open it, follow the instruction inside and replace it by my self..
turn on the power back with a new thermostat and its working. the furnace stop
when it reach the set temperature...
but i notice again the blower fan still running all the time.it only stop if i
switch OFF the power at the furnace. should be auto off when it reach the set
temperature.. ANY HELPFULL ADVISE will be apreciated
THANK YOU IN ADVANCE>>
If the furnace controller is NOT set to always provide fan, the culprit
could be the thermostat wiring. Remove the wire connected to the G terminal
at the furnace, typically a green wire. If the fan stops, the wiring is
causing the fan to run.
I am assuming the two thermostats are not both defective !
When runs how long did you wait. An hour or longer and still running?
If furnace has cooled down and fan is still going, hi limit switch stuck
closed, fan relay on the control board stuck closed, etc. could be the
I went through a similar exercise a few weeks ago. The furnace would
heat and cool normally, but the blower ran constantly. I determined
that the problem was not the thermostat but was unable to troubleshoot
it any further, so I called a repairman. It turned out that the main
computer board in the furnace had gone bad and had to be replaced. Many
furnaces like mine are so computerized that there aren't very many
small replaceable parts inside - much of the system is integrated into
On Friday, February 13, 2015 at 1:49:36 AM UTC-5, Nil wrote:
It certainly could be a defective controller board in the furnace.
Possible it's the wiring between furnace and thermostat too where a
short has occured. Or it could be that the new thermostat is wired
incorrectly, check the fan wire, which is usually green. Also a
simple test would be to locate the other end of the fan wire at the
furnace and disconnect it. If the fan still runs, it's the controller.
If relay is stuck, it can be replaced with some soldering skill. If
logic controlling the relay is bad little harder to deal with it,
but still repairable. When run into ASIC, it is almost impossible to
get a replacement chip. They charge few hundred $$ for a replacement
board. It is not really a computer but contains micro processor chip.
It is possible that the contactor that senses the air flow temperature in t
he furnace is stuck closed, resulting in the blower running continuuously i
nstead of shutting off when the air flow temperature is below some set tem
perature. My funace sensor started sticking, I could get the contacts to o
pen by banging on the furnace plenum near where the sensor was located. Go
t to be a nuisance, so went to myh local parts store with the old sensor an
d got a new one. Less than 25 bucks.
Thank you guys to your ideas you have put in here...after reading of all those
comments i might have to call a repairman to fix it. i convince my self that it
might be the control board problem...
thank verry much.
About a decade ago, I got a call from a friend from church, who had a
furnace failure. He was at work, and his wife was home with the kids. I
went and asked what had happened. Well, for some reason the circuit
breaker tripped. This was summer, and they were using the AC. Nice warm
day, too. As the breaker had tripped, no cooling, and they wanted to be
cool and comfortale.
I chatted with the wife. She said that the circuit breaker was off, so
she turned it on. It tripped right off again. So, she reset it (dozen or
more times) and finally the circuit breaker stayed on.
I started to check things, and found out that the fan blower mtoor had
developed a short. Each time she reset the breaker, the furance tried to
power the fan which was dead short. So, the breaker tripped again.
Finally, the contacts on the fan relay on the circuit board vaporized,
and the breaker stayed on.
Was a decade or so ago. I remember the fan motor was about $60 and the
circuit board was about $200, had to get it throught he carier Bryant
place, and they didn't go cheaply.
to the OP, might want to research, might find board for sale online
cheaper than having a tech out.
Christopher A. Young
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