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Goodman Gas furnace
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When troubleshooting, understand you are working with potentially lethal voltages and a highly flammable gas. If you do not have the ability to do these operations safely, do not attempt them.
Janitrol Model GMP 050,075,100 or 125.
These furnaces were installed from the late 80s to present. They are 80% efficient furnaces and they vent with metal pipe.
They are induced furnaces, meaning they use a fan to extract the burned gasses from the heat exchanger and into the vent. The video below gives sequence of operation of an 80% efficient furnace and the model used is a Janitrol GMP 075 model.
These furnaces were installed from the late 80s to present. They are 80% efficient furnaces and they vent with metal pipe.
They are induced furnaces, meaning they use a fan to extract the burned gasses from the heat exchanger and into the vent. The video below gives sequence of operation of an 80% efficient furnace and the model used is a Janitrol GMP 075 model.
Sequence of operation of this furnace is similar to most 80% furnaces made after 1990.
1. On a call for heat (thermostat closes), a signal is sent to the IFC and sequencing begins.
2. The IFC electronically looks at the pressure switch.
A. If the pressure switch is open (power cannot pass through), the IFC starts the inducer.
B. If the pressure switch is closed (power passes through), sequencing stops and IFC goes into lockout mode. Lockout code will displayed on the IFC by blinking lights on the module. (key to codes should be listed on the furnace panel).
C. Most IFCs will attempt to try again 10 to 15 minutes later.
3. Once the inducer starts, the pressure switch should close.
A. If the pressure switch does not close, the inducer will continue to run for 1 to 2 minutes then will lockout and try again 10 to 15 minutes later.
B. If the pressure switch closes, the prepurge will begin.
4. The IFC will look at the limit switches.
A. If any of the limit switches are open, the furnace will lockout, the circulating fan will come on and a lockout code will be displayed.
B. If the limit switches are closed, the the warmup time for the HSI begins. A yellow glow will come from one side of the burner box.
5. The HSI warms for from 10 to 45 seconds.
6. The gas valve opens for 4 to 7 seconds to allow gas to pass into the burners. This is called the "trial for ignition"
7. If the burners ignite, the flame is proven, usually by flame rectification, during this time. The flame is sensed by a flame rod on the opposite side of the burners as the yellow glow. There should be a blue light in the burner box.
8. If the burners fail to ignite, the furnace shuts off the gas supply, goes through a purge cycle and attempts to light the burners again.
9. The furnace tries a total of 3 times, then if flame is not established goes into hard lockout. A lockout code will be displayed on the IFC.
10. After 1 hour, the furnace will start the entire sequence again to try to fire off.
11. If the flame is proved, a timer is started to delay the start of the circulating fan for 30 to 40 seconds.
12. When the call for heat is over, the burner extinguishes. The circulating fan continues to run for 2 to 3 minutes to clear heat from the heat exchanger.
13. This sequence is generic. Some furnaces will vary in their actual sequence, but will be substantially the same.
2. The IFC electronically looks at the pressure switch.
A. If the pressure switch is open (power cannot pass through), the IFC starts the inducer.
B. If the pressure switch is closed (power passes through), sequencing stops and IFC goes into lockout mode. Lockout code will displayed on the IFC by blinking lights on the module. (key to codes should be listed on the furnace panel).
C. Most IFCs will attempt to try again 10 to 15 minutes later.
3. Once the inducer starts, the pressure switch should close.
A. If the pressure switch does not close, the inducer will continue to run for 1 to 2 minutes then will lockout and try again 10 to 15 minutes later.
B. If the pressure switch closes, the prepurge will begin.
4. The IFC will look at the limit switches.
A. If any of the limit switches are open, the furnace will lockout, the circulating fan will come on and a lockout code will be displayed.
B. If the limit switches are closed, the the warmup time for the HSI begins. A yellow glow will come from one side of the burner box.
5. The HSI warms for from 10 to 45 seconds.
6. The gas valve opens for 4 to 7 seconds to allow gas to pass into the burners. This is called the "trial for ignition"
7. If the burners ignite, the flame is proven, usually by flame rectification, during this time. The flame is sensed by a flame rod on the opposite side of the burners as the yellow glow. There should be a blue light in the burner box.
8. If the burners fail to ignite, the furnace shuts off the gas supply, goes through a purge cycle and attempts to light the burners again.
9. The furnace tries a total of 3 times, then if flame is not established goes into hard lockout. A lockout code will be displayed on the IFC.
10. After 1 hour, the furnace will start the entire sequence again to try to fire off.
11. If the flame is proved, a timer is started to delay the start of the circulating fan for 30 to 40 seconds.
12. When the call for heat is over, the burner extinguishes. The circulating fan continues to run for 2 to 3 minutes to clear heat from the heat exchanger.
13. This sequence is generic. Some furnaces will vary in their actual sequence, but will be substantially the same.
Janitrol 80% furnace error codes
1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. Interpret five LED flashes to mean your Goodman furnace senses a flame without a call for heat. This could be from a gas valve closing slowly or a burner flame lingering.
7 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.
8. 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.
9. 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.
10. 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.
Troubleshoot videos
The video below begins the troubleshoot of the Goodman 80% furnace with an overview of common failures with this furnace.
This video explains how to troubleshoot the over temperature limit that shuts down the burner if the temperature inside the ductwork is too high.
The pressure switch
The pressure switch is a safety control used to determine if the air pressure inside the furnace is correct for safe and efficient operation of the furnace.
The pressure switch is a diaphragm switch that operates on .2 to 1.8 in wc
pressure. These are very low pressures and the diaphragm is used to multiply the power of the pressure. Because they can easily stick, a safety circuit must be used to be sure the pressure switch is not stuck closed. This circuit is located in the IFC . If the furnace begins to fire and the switch is closed, the sequence stops. If the switch is open, power is sent to the inducer and it starts. The switch, which has a sensing tube communicating with the inducer housing, must then close within 1 to 2 minutes depending on model of furnace.
If the inducer does not run, the vent pipe is plugged, the blower wheel is damaged, the pressure switch is stuck open or any other failure prevents proper vacuum, the IFC will shut down the sequence and blink a code on the IFC. The following video explains the troubleshoot of the pressure switch. Remember, the pressure switch is often the sign of trouble and not the source.
The pressure switch is a diaphragm switch that operates on .2 to 1.8 in wc
pressure. These are very low pressures and the diaphragm is used to multiply the power of the pressure. Because they can easily stick, a safety circuit must be used to be sure the pressure switch is not stuck closed. This circuit is located in the IFC . If the furnace begins to fire and the switch is closed, the sequence stops. If the switch is open, power is sent to the inducer and it starts. The switch, which has a sensing tube communicating with the inducer housing, must then close within 1 to 2 minutes depending on model of furnace.
If the inducer does not run, the vent pipe is plugged, the blower wheel is damaged, the pressure switch is stuck open or any other failure prevents proper vacuum, the IFC will shut down the sequence and blink a code on the IFC. The following video explains the troubleshoot of the pressure switch. Remember, the pressure switch is often the sign of trouble and not the source.