Armstrong air tech 91 furnace problem

Try cleaning the flame sensor First . Then check pressure switch.

Generally sounds like they are thermostats

There should be a diagnostic chart on the furnace door by the wiring schematic. If so see what the code reads for three blinks.
By the term "air combustion switch" I guess you are referring to the pressure switch. Most diagnostics blinking three times is just a dirty flame sensor. If this is the case the burners will light and go out within 4 seconds. If this is the problem carefully remove the flame sensor and clean gently with emery cloth, fine sandpaper or fine steel wool. Reinsert the sensor and enjoy your heat.

Have you checked the flue inlet and outlet to see if it doesn\'t have a wasp nest or bird nest or rocks. check the hose that is attached to the pressure switch and the port on the collector box or inducer fan motor to see if it is clear. if you take the switch off and lightly suck or blow into the port it that will close the switch. If you have a manometer you can check the pressure differential. On the pressure switch it will say what pressure in will close at ...Example .52" WC. or 1.25"WC You would attach your manometer to the tube attached to the pressure switch and start the combustion blower to read the pressure. If you have over the reading and the switch didn\'t make you will need to replace the switch. if you have less than you have to make sure the flue is open. You can check the flue with a simple trick by unhooking the flue pipe from the combustion blower and then check the pressure and you may have to unhook the air intake also. If that doesn\'t work you could have a plugged secondary heat exchanger...... Good Luck.

Most pressure switches run off of a vacuum not pressure, when the inducer starts it actually creates a negative pressure that closes the switch, most boards require the switch to be open on initiation then after the inducer starts it must close, you could **** on the tube and see if you hear it click, or test with a meter for continuity. Draft problems can cause carbon monoxide and kill so do not attempt to jump out a pressure switch or any other control other than for testing purposes. I hope this helps and if it does give me a thumbs up

Did he check the Pressure switch was it filled whit water can you make the switch open on the pressure switch when blowing on it? Is the hose from the inducer motor opened and not blocked ? also if there is a block after the inducer motor it will not Ignite. If the Tech does not know how to check a pressure switch get a new tech.

Hello, this indicates a open limit switch. A limit l switch will open when the temp in the heat exchanger gets too high and this switch shuts the Furnace down for safety. Usuaully a dirty filter, weak blower motor, dirty blower wheel will cause a limit switch to open.

Installed a new filter and furnace is running great now. The old filter was not that old, but we have been doing some remodeling and I figure that is what clogged it so fast.

These furnaces goes thru 4--steps for complete run time.... step-1, the small draft inducer blower motor blows and prove thru the small air tube that sucks a switch close to tell the circuit board to go to step-2......the glow plug glows for 15 seconds and step 3 the gas valve opens and dump gas in the venturi tubes and lights off the glow plug and proves thru a flame sensor (pin with 1 electrical wire connection) on the last venturi tube which tells the circuit board to go to the last step 4--, to turn on the main blower fan after 90 seconds!. Where ever it stops at then thats where your problem is!

If you know where the high limit switch is you can always cut the two wires and wire them together causing the limit to close. But what you have to watch out for is why the high limit is not closing. That means in your return air either you have a dirty return air duct, dirty filter, or you don't have all your registors open to allow the heat to escape the heat exchanger. Just watch over riding the system. The high limit switch should either be on or behind the blower, in the middle of the system right under the heat exchanger. any other questions about hvac just ask.

David