Originally Posted By: cmccann This post was automatically imported from our archived forum.
I inspected a home the other day with a Bryant Furnace forced air Model # 394GAW036100. Now I know it’s a 100,00 BTU but according to Preston’s guide It could be anything from a 1982 to 1989. My real question is after turning up the thermostat I waited for the fan to kick on. NO fan, I went to the basement and found the unit trying to light. After about 1-2 minutes the furnace lighted and after about 3-4 minutes the fan came on. My experience is that the fan should come on first before the furnace lights the burners off. Am I wrong? My Bryant is a 1990 125,000 and the fan comes on first. I figured the fan has to come on first to move any excess gases and so the heat exchangers don’t over heat waiting for the fan to come on. Any help would be great, I’ve already explained that the unit was operating incorrectly, and they agreed, but if I’m wrong I want to call the agent ASAP to tell her I messed up. Thx
Originally Posted By: Blaine Wiley This post was automatically imported from our archived forum.
Chuck,
Bryant furnaces have their date in the Serial number.
The fan is supposed to come on after the heat exchanger heats up, otherwise you will be blowing cold air through the house. Typically the fan will come on about 120 degrees, give or take a bit, and shut the fan down around 95 degrees, give or take a bit.
The only fan that will come on prior to ignition is an induced draft motor, which is on 90+ furnaces.
If the pilot light is having trouble lighting or staying on, could be a thermocouple. Recommend service.
Originally Posted By: rkulla This post was automatically imported from our archived forum.
Some electronic thermostats have settings on the back for different types of furnaces. They can make the fans do some strange things if they are set-up wrong.
Originally Posted By: jpeck This post was automatically imported from our archived forum.
Most newer furnaces, for improved efficiency numbers (which is what many improvements are all about), only turn the fan on after a preset time delay. This allows the burner to create heated air before the fan comes on and begins to circulate that air out of the furnace.
Then, to accomplish the higher efficiency numbers on shut down, the fan runs after burner shuts down, for a predetermined time delay, to remove as much of the heat produced by the unit as possible.
Originally Posted By: jmyers This post was automatically imported from our archived forum.
I agree the fan turns blower fan turns on after the unit come up to temperature. It may be a little more simpler than you think. I came across a unit just as you described that was functioning incorrectly. It was a natural gas unit and would turn on and fire for a few minutes then turn off. The blower would never turn on. After taking the blower cover off this unit, it still did not function until I hit the blower door to put it back on. Apparently the safety switch on the unit was not properly engaging until I hit the door. It could be a bad safety switch on the blower door too.
Originally Posted By: cmccann This post was automatically imported from our archived forum.
Everyone is right. The blower does not turn on until the exchanger comes up to temp. The problem is that my own house unit is not working properly. The fan (blower) comes on before the burners light. I have been trouble shooting this with Tom Pope in Spokane of the Northwest HVAC training center… I have sent pics and we are currently trying to figure out why this is happening. There is no adjustment for the fan, it seems it has been jumped. Stay tuned…thanks
Originally Posted By: jpeck This post was automatically imported from our archived forum.
Chuck,
I'm sure he has already checked the delay timer ... but have him replace the delay timer, it may work when tested, but not when 'in use'. Sounds like the delay timer is no longer waiting through its time delay period.
Instead of a delay timer, it may have a temperature sensor above the heater section (where the high limit switch is), and this may becoming 'satisfied' (has gone bad and is always indicating 'on') without heat. Thus, as soon as power is applied, the fan comes on, because this sensor is saying 'okie dokie, heats on, crank 'er up'.
I am assuming that it used to work correctly, right?
Originally Posted By: cmccann This post was automatically imported from our archived forum.
Holy Crap, Rolland I took the Honeywell Thermostat off the wall and there was a switch for E or F, The indicator was in the middle I moved it to the F and the burners lite off first then the fan. That is cool. Thx I hope it continues to work. Drink a Sierra Nevada for me.
