The draft inducer starts, but pilot burner only clicks and lights when burner compartment cover is off.

It is a natural gas furnace. It has a 3 wire pilot burner. When the thermostat calls for the furnace to turn on, the draft inducer motor starts running, but the pilot burner is not even trying to light, no clicks no sparks, nothing. If I take off the cover of the burner compartment, the furnace fires right up and runs like there is nothing wrong.

Check for air restrictions in the combustion air.

Probably the pressure switch: http://www.xpedio.carrier.com/idc/groups/public/documents/techlit/iik398a-40-4.pdf#xml=http://www.xpedio.carrier.com/idc/idcplg?IdcService=GET_XML_HIGHLIGHT_INFO&QueryText=dDocTitle+%3Csubstring%3E+%60398a%60+%3C OR%3E+dDocName+%3Csubstring%3E+%60398a%60+%3COR%3E +%28398a%29&SortField=dInDate&SortOrder=Desc&dDocName=IIK398A-40-4&HighlightType=PdfHighlight

Schematic is here:
http://www.xpedio.carrier.com/idc/groups/public/documents/techlit/wd398a.40.1.pdf#xml=http://www.xpedio.carrier.com/idc/idcplg?IdcService=GET_XML_HIGHLIGHT_INFO&QueryText=dDocTitle+%3Csubstring%3E+%60398a%60+%3C OR%3E+dDocName+%3Csubstring%3E+%60398a%60+%3COR%3E +%28398a%29&SortField=dInDate&SortOrder=Desc&dDocName=WD398A.40.1&HighlightType=PdfHighlight

Switch 7P.

The schematic isn't helpful.

First attach a voltmeter between the C and NC contacts and operate with the door open. There should be a change of state. I suspect it's 24 VAC although it's impossible to tell.

Then run wires out a hole to the meter and put the cover on.
Check for the same change of state.

With the burner enclosure open, look up through the strainer in the air vent coupling. If debris is visible, remove pipe and clean out. Also check outside vent terminations for blockage.

Thanks, I tore it apart cleaned it good, but didn't find any obstructions, I tapped(beat on) on the pressure switch and it has been working for a couple of days now, I got a new pressure switch for when it does happen again, I will be ready with a replacement.

Might as well replace the switch now since it will break again when its 20 below zero and you just got home from work if you know what I mean.