First you need to know what kind of furnace it is that is having issues.
Goodman furnace sequence of operation.
Hi martin the gas valve should turn on right when the spark ignitor starts if you don t smell any gas or hear the valve open then your probably not getting that far in the sequence on a call for heat the first thing it will check is the safeties as it turns on the inducer motor most furnaces use the air switch to verify the inducer is running if there is a problem with the air switch the inducer motor may continue to run but it will stop the starting sequence try rapping on the air.
Control board does a safety check limit switches roll out switches.
Sequence of operation of this furnace is similar to most 80 furnaces made after 1990.
Dip switch settings gmec furnace.
Then you need to know the sequence of operation for the furnace if you are to troubleshoot the furnace properly.
Inducer motor comes on.
The inducer motor begins to spin and creates a vacuum to insure the left over gasses go out the exhaust pipe.
Heat call from the thermostat.
Knowing the sequence of operation will help in troubleshooting a gas furnace.
The sequence of operation may vary depending on type or brand.
Sequence of operation gmvc96.
Off the manual gas shutoff valve external to the furnace before turning off the electrical supply.
Sequence of operation this appliance communicates with room thermostat through the low voltage connections described in thermostat location and low voltage connections section of this manual.
Sequence of operation gmec96.
A sensor detects if there is a vacuum created by the inducer motor if there is it closes a switch if there is no vacuum the switch is left open.
Front cover pressure switch.
The video below gives sequence of operation of an 80 efficient furnace and the model used is a janitrol gmp 075 model.
The thermostat reaches a set temperature and sends a signal for the furnace to turn on.
Such as unventilated garages utility rooms or parking areas because of carbon monoxide poisoning hazard b10259 216 special warning for installation of furnace or air handling units in enclosed areas such as garages utility rooms or parking areas.