Gas Armstrong Ultra V Tech 91-Is green light supposed to flash?

BE VERY CAREFUL WORKING WITH A GAS FURNACE.

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

start at the fuse and work up to the electrics that the wire controls
It is a dead short somewhere

Hit the side of the furnace. Some times there's a sensor inside that gets locked up from a dirty filter.

Hi try this site, http://www.furnaceparts.com/  Good Luck

if it has a pilot, you can follow the pilot tube from the gas valve back to the burner assembly and find it. It may not have one and if this is the case, the air flow switch is supposed to close when the inducer fan comes on . If the flue is clogged, condensation in the bottom of inducer fan(would hear cracking). then after the draft safety switch is closed,the gas vavle will get 24 volts and allow the gas valve to open

You have a dirty flame sensor. Look at the very last burner and you will see a wire going to a ceramic sensor and it looks like a thick wire. Take some steel wool or fine sandpaper and clean the surface off and it will work like a champ.

Let me know how it goes ken

Sounds like the flue is plugged, I had same problem and opened up the draft fan and there was a dead bird restricting the flue. Furnace will never light if the pressure switch never closes as you have found out. Also has anyone moved the switch some are position sensitive meaning have to be in same position factory set the switch. I had one like that also switch was little crooked so I straighten it up and walla worked.

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!