I have a customer with a evcon direct vent forced hot air furnace. The thermostate calls for heat , the combustion fan comes on then the ignitor lites and the burner comes on for about 2 minutes, jsut before the main blower comes on, the burner shuts off and then the blower starts, after about 1 minute the cycle begins again. Not sure whay the burner shuts off just before the blower comes on?

main fan should come on once furnace has heated up to supply hot air to the house. make sure proper voltage going to the fan. fan relay in board may be shot

On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the ignitor. The ignitor will glow and you will be able to see it if viewed thru the small inspection port. Once the ignitor gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.

What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the ignitor does not energize (bad control, bad ignitor), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not lite (dirty pilot), the burner does not lite (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).

Most newer furnaces will have a diagnostic center or control built into the control module. You may be able to view it as it is running thru a small viewing port. Some models will require the removal of an access panel prior to finding it. On the reverse of the access panel, there will be a diagnostic chart that will aide you in understanding any error code recorded (usually a blinking light).

the fan you hear come on at a call for heat is most likely just the inducer motor. the click you hear is probably the relay for the hot surface ignitor which should glow red, then in turn ignite the main burners. your going to have to determine if the ignitor is coming on. if it isnt the ignitor is bad and will need to be replaced. if it comes on and than shuts off after a few seconds the ifc board is probably at fault

if your power vent moter is not running you should not have have glowing ignitor.Frist the vent moter must close an air prove switch in series with the idnitor .seems you have a stuck air prove switch.Its the one with a hose attached

Does your condo have more than one thermostat? if so there are powered dampers that open and close to direct heat where it's being called for. You may have dampers stuck/inoperative.

Have you tried to replace pressure switch for the combustion air. If your not sure where to find it if you pull the front panels off follow the flue pipe down to combustion chamber the combustion fan motor is either inside the flue pipe or out side of it not sure on the one you have but you should see two plastic tubes that connect to a barb onto the topside of the fan and one on the bottom they both should go back to the pressure switch. i hope this helps you if you have any more question or if this doesnt fix the problem just reply back to this message . Make sure fan is working when furnace starts up. It should be the first thing that comes on when there is a call for heat

Looks like 4 flashes might be high limit fault on this furnace. (I don't have a manual for this furnace, just searched online for the code meaning) Is the unit running flame at all? Is the unit running flame for a while then shutting flame off before desired temp is reached? Does the main air fan turn on to circulate air through your diffusers? Does it feel like the unit has much air flow out of the diffusers if the fan is running? Is your air filter clean? If it is infact your high limit switch, it is usually caused by not having enough airflow through the furnace and overheating occurs.

Hope this helped, let me know if I can assist you further :)

Small blower motor? Are you talking about the combustion blower if so then check your vents for blockage.. if the vents are blocked won't work... if it has a control board init it will give you a diagnostic code. Flashing light on the board... count the flashes and look up the fault on the chart in your owners manual ot on the furnace door..

Defective combustion air switch. The 3 blinks are an error code. You didn't say, but I'm guessing you have a Coleman Evcon. They had alot of defective Combustion air switches. Your specialists were not that.

Sequence of operation, Gas Furnace.

On a call for heat, the 24 volt thermostat sends a signal to the control module. The control module will indicate a call for heat with a light on the control either blinking or remain solid depending upon model. The inducer (exhaust) blower will purge all gasses from the furnace and pressurize a pressure switch. Once the pressure switch tells the module to continue, the electronic ignition will energize and send 120 volts to the ignitor. The ignitor will glow and you will be able to see it if viewed thru the small inspection port. Once the ignitor gets hot enough, it sends a signal to the module opening up the gas valve (24 volts). Either a pilot will come on or the burner tube will ignite then spread the flame to all burners. Lastly a safety sensor will be looking for a certain temperature within a few seconds and the furnace will continue to operate and the room air blower will turn on in a minute or two.

What could go wrong? The unit will not run if there is no signal from the thermostat (bad thermostat or broken wire), the control module does not sense a signal from the thermostat (bad control), the inducer does not energize (bad motor), the pressure switch does not close (blocked vent piping, bad switch, plugged condensate hose), the ignitor does not energize (bad control, bad ignitor), the gas valve does not open or there is no gas (bad gas valve, broken wire, no gas), the pilot does not lite (dirty pilot), the burner does not lite (bad burner, plugged orifice, not enough combustion air), the flame does not spread to each burner (bad flame spreader, dirty flame spreader, more bad burners), the flame safety sensor does not detect flame (dirty or bad flame spreader, bad flame sensor, broken wire, bad control), or the room air blower does not energize (bad fan motor, bad control).

Most newer furnaces will have a diagnostic center or control built into the control module. You may be able to view it as it is running thru a small viewing port. Some models will require the removal of an access panel prior to finding it. On the reverse of the access panel, there will be a diagnostic chart that will aide you in understanding any error code recorded (usually a blinking light).

This is why we technicians earn the big bucks!