Code is flashing on my Coleman Furnace ...Combustion air switch failed to close...we have already replaced the pressure switch ....What else could it be???

Steady light on - normal operation.
One flash - ignition failure.
Two flashes - combustion air switch stuck closed.
Three flashes - combustion air switch failed to close.
Four flashes - limit switch open.
Five flashes - gas valve energized with no call for heat.
Rapid flashing - reversed polarity.

Note: Color of light is green.

jump out pressure switch see if it lights check hose to pressure switch see if they are split or connections are not good ,cut off ends and put back on presure switch.

Hi, new switch can be found on amazon... here: Amazon com Coleman air switch. I hope this was helpful. Cheers

I have had the same problem with mine for the last 2 years. Remove the motor on the side of the furnace(usually held on by 3 screws) and turn the fan blades inside by hand. after sitting all summer it seems to get stuck. If it moves freely, replace the motor and try to start it again. This fixed mine the last 2 years! Hope this helped.

The combustion air switch is closed by the air pressure from the draft inducer fan. You can check it with a voltmeter. When the heater starts to run check the voltage reading where two wires connect to the switch. It should be 0 vac if the switch is closed. Instead of starting the furnace, you could also remove one end of the rubber hose that goes to it from the draft motor and blow into the hose and see if that closes the switch. It may be just stuck. I almost forgot to mention the most important thing; make sure the draft motor is running. Let me know what you find. The air pressure switch is a safety feature to prevent the furnace from running if there isn't enough air supplied to the burner for proper combustion.

Combustion switch is your vent safety.. Check your vents outside for blockage, sometimes the intake pipe will freeze or frost up not allowing the preassure switch(vent safety)to close. putting furnace into a lock out.. you can reset the furnace by turning the power on and off.. if there is no power switch just remove the bottom door and reinstall...

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.

could be bad switch but is the vent free and open of all debris or being blocked by anything

check for a blocked flue pipe

Your centrifical swith is stuck open on your blend motor. I found that removing the blend motor housing and spinning the stuck motor (from setting over the summer) will get you out of a bind ,.but you may end up needing this centrifical switch (locatedon the bottom of the blend/fresh air intake) motor replaced.