Pressure switch is not proving that the inducer fan is running. First check to see if draft inducer fan is running that will be the small black fan that is hooked to the vent pipe. If fan is not running then replace fan. If fan is running then check the small rubber tub that runs from inducer blower blower to draft switch make sure the hole in the blower cage is not stopped up with rust you can clear this with a sewing needle. If this is clear then check the pressure switch with a volt meter make sure it is getting 24 volts to the switch and through the switch. If it is getting to switch and not through switch then replace the switch.
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The induced draft motor has a induced draft proving switch that is a pressure switch , it resembles a silver round flat device about 4 inches across with 2 wires, it will have a tubing attached to it that also is attached to the induced draft assembly housing on a barbed port, this is how the induced draft is "proven" thus giving the A OK to go to the next sequence of operation which is ignition trial period, it will attempt a ignition sequence for about 30 seconds 3 times before it will lock out if it has a circuit board, if so a flashing code will be observed and the legend in the back side of the blower door will tell you the codes meaning.
What is wrong 80% of the time is the barbed port on the induced drafts assembly is obstructed by carbon and not allowing the pressure switch to "sense" / prove the induced draft motor is running. You can connect the pressure switches 2 wires after the induced draft begins, this simulates a operational pressure switch and should begin the ignition phase if all is well, otherwise if all safety's or high limits are closed, then the ignition module is bad.
This is for spark type, if you have a hot surface ignitor look to se if its broken or cracked or has a burned spot visible, if not try testing for 120 volts to it, if you read proper voltage, then the hot surface igniter is bad.
Almost all furnaces built after 1978 have intermittant type pilots.
Ca banned them requiring electronic spark or hot surface ignitors, followed by induced draft motors, pressure switches or centrifigal switches that "prove" a induced draft exists, allowing the pilot sequence to commence.
electronic spark type units have a high voltage low amperage spark that is AC. Fire rectifies electricity that passes through it meaning AC becomes DC ! Fire is a terrible conducter however as a result , the DC signal is only milliamps/volts signal strength. the DC prescence is proof a flame exists for pilot, and safe to commence to mainburners.
As long as pressure switches stay closed, safeties and limits stay closed
and the DC signal to the ignition module is not broken, the furnace will run.
The normal sequence of operation is upon a call for heat from the thermostat a 24 volt signal is sent to W white (heat circuit) at the low voltage terminal board on furnace.
from there depending on unit and age the heat circuit may include a circuit board, but it still has the typical limits and safetys reqired for operation
its just not using electromechanical relays to control fan and induced draft motor etc.
for the induced draft to begin ,all limits, safetys in heat circuit must be closed.
induced draft begins and a proving switch, either pressure or centrifigal close allowung the pilot to begin, a spark or hot surface ignitor is energized and a pilot flame established,modern types use flame rectification to prove a flame, older Carrier, Payne,types have a 3 wire switch in the piloyt assembly that is a bi metal that expands and contracts clicking open and shut, allowing pilot or main burners, depending if cold or hot.
pressure switches are attached with tubing to the induced draft wheel housing and sense pressure differential and close upon induced draft running, the orifices that the tube attaches to on induced draft housing often plugs or is restricted causing pressure switch to fail to close, or waver on open and close , open , close, .
if you can run the fan in the on postion , you have both high and low voltage to the furnace.
if you dont have fan control check power, breaker , fuses.
Check polarity to the furnace, it must be correct, not likely unless new or worked on though. The induced draft has a pressure switch that has a tube that connects to the induced draft housing, that orifice clogs with carbon and a tiny drill bit is used to **** the orifice clean, it will be hard if pluged, you know you are clear when you fel,hear the inducers squirrel cage with the drill bit, the tubing if dipped can collect condensate and block the pressure of the draft to be sensed by the pressure switch and the pressure switch can be bad or off too. If the flue is blocked or induced draft wheels burned up/rusted out, not much draft is induced, you need to snoop a bit.
Check for a bad hot surface ignitier, they generally will burn white hot and if bad may be cracked visibly with a grey area marking the crack. the unit will attempt a trial period for ignition 3 times and if not succesful will lock out. a pressure switch to the induced draft motor may be unabe to sense the pressure due to moisture in a low spot in the tube connecting the induced draft housing to the pressure switch, more often the orifice on the inducers housings plugged by carbon and needs a tiny drill bit to **** it out clear. switch itself will fail too.
Hello, it sounds like the pressure switch is not closing on your furnace and remaining open, reasons for this could be a blocked flue pipe, the tubing going from the inducer motor to pressure switch could be blocked, loose, or have condensation in it, or the switch itself is bad. U can check the tubing by taking it off blowing some air through it and making sure no condensation is in the tubing, then reinstall it. If everything checks out good then the pressure switch is bad and must be replaced.
That thang might be sensing a lazy flame. In other words the flames took too long in the board's opinion to quit sensing the flame. Yall probably need to do pressure tap on the gas valve. Here is a realistic look at goodman fault codes and what to check fer and I am assuming you are not a tech and don't know this already and am hoping it helps:
Read one LED flash that stays on continuously to mean your furnace has no signal coming from the thermostat and will not operate. Turn the power off and check the thermostat for improper settings or connections.
Interpret one LED flash that blinks on and off to mean your furnace has locked out because it could not ignite after three tries, and must be reset. Interrupt power to your furnace for 20 seconds or lower the thermostat so your furnace does not try to heat, then reset the thermostat to the previous setting. After one hour of lockout, your furnace will automatically reset itself and try to operate as usual.
Decipher two LED flashes to mean the draft blower is not working, or your furnace has a short in the pressure switch circuit. Turn off the furnace power and repair a short or replace the pressure switch.
Read three LED flashes to mean your furnace has an open pressure switch circuit or it has an induced draft blower operating. Check the pressure switch hose of your furnace for blocks or an improper connection. Also, look for blockages in the flue, and tighten any loose wiring.
Translate four LED flashes to mean your furnace has a primary limit circuit open, possibly from loose wiring or blocked filters. Check and clean filters, tighten wiring and check the flue for blockages.
Interpret five LED flashes to mean your furnace senses a flame without a call for heat. This could be from a gas valve closing slowly or a burner flame lingering.
Read seven LED flashes as a warning of a low flame sense microamp signal. This could happen with a coated flame sensor or a lazy flame from poor gas pressure. Turn off the power and adjust the gas pressure according to the information on the rating plate.
See eight LED flashes as meaning an igniter circuit problem due to a bad igniter or an igniter connected improperly. Replace the bad igniter or check the ground wiring, making necessary corrections.
Decipher nine LED flashes to mean the high-stage pressure switch circuit will not close during a high-stage-induced draft blower operation. Your furnace may have a pinched or blocked pressure switch hose, a blocked flue or loose wiring.
Read continuous flashing on the LED to mean your furnace has a reversed polarity of 115 volts. Turn off the power and correct the wiring polarity after reviewing the wiring diagram.
Now here is how it should all go down:
Bottom dollar: it all goes back to type of gas, the initial setup, the pressure tap. and how it is wired up to begin with. This will give you an idea where to start I hope.
f this is a metal vent 80% furnace,Turn Furnace off and remove the vent that connects to furnace and see if it is plugged.
If this is a High Eff furnace witrh pvc vents for exhaust and intake air make sure they are not plugged on the outside.
Turn thermostat all the way up,turn furnace off and wait a few minutes.This should reset any control board fualt.
Turn the furnace back on, if you have a glow coil ignitor it should glow red and then the burners should ignite. If this doesnt happen then:
On High Eff Furnace if the glow coil does not glow red, remove the combustion door to the burners, turn furnace back on, if the glow coil glows and burner ignites, you have an obstruction in the intake air side. If it still does nothing then:
Use caution and remove the exhaust vent from furnace, start furnace, if furnace runs then you have a problem with the vent system
it may be clogged at the barbed fitting on the induced draft motor where the pressuer switch tubing connects. take a paper clip and **** it out make sure you can stick it thru freely till you can feel the Inducer wheel then reconnect and try again.
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