Spec sheet
http://www.airease.com/pdfs/jg1n80btur-100.pdf
Make sure your air intake is open if so equipped on that 80% unit.
Does the circuit board flash or blink a code when in the failure mode?
If so post the code(number of blinks) and the meaning. The legend for this will be on the back side of the blower motor access door.
A problem such as this is very difficult to fix on the net, Since it only does this when the door is installed I suggest you start by checking all wiring for tightness especially if you have the Honeywell smart valve sometimes called the dumb valve by folks in the trade. Your furnace is made for various manufactures including Armstrong and the problem with condensation dripping from the flue pipe on to the gas valve is well known. This inturn damages the electrical connections on top of the valve rendering it damaged. Hete is a posting by a company that sells replacement parts. It covers that quite well but there part prices are way to high in my opinion.
Check the wiring in the furnace.
Check the wiring and move it around a bit on the top of the gas valve.
Then post back with what you find.
Here is link to gas valve problem and I guess you have the Honeywell if you have this style of unit.
Armstrong, Honeywell Upgraded Smart Valve 1/2 in. NPT x 1/2 in. NPT Intermittent Hot Surface Pilot Ignition SmartValve™ Control with slow opening and 3.2 in. wc pressure regulator setting (3-Molex Plugs): Best Buy Heating and Air Conditioning