Carrier Weathermaker (58MXA) code 31

Hi! I have a problem w/my Carrier Weathermaker 9000? (it's a 58MXA) not heating.
Though the "component test" checks out OK, this is the ONLY time that I see that I see the HSI energized (the ignitor). Also, the test of the pressure switch in the op's manual (i.e., disconnect the inducer motor, call for heat, and make sure that the HSI is NOT glowing after about a minute) was fine.
I see a steady ~26VAC signal to the pressure switch.
Other checks:
- air intake/exhaust not clogged (good flow when inducer runs) - inducer motor supply voltage fine (>120VAC) - inducer cap fine (3.0 uF and resistance huge @ DC) - install was years ago so PVC sizing must be right - no backup of water in the drain system - no clogging of the other rubber/plastic tubing (from the pressure switch to the burner box)
So am I at a point where the board is in question or might it still be the pressure switch?
I've tried shorting across the terminals, but an HVAC tech has informed me that not doing it at the proper time or with the connections previously ok (i.e., apparently you can't just disconnect the leads and short the terminals) won't show the proper behavior.
??? HELP!
Thanks
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On Tue, 30 Oct 2007 10:32:23 -0700, snipped-for-privacy@umich.edu wrote:

Code 31 is for the pressure switch not making. Check the following: is the inducer motor running, are you getting 24v on both sides of the switch, is the flue pipe obstructed, is the rubber hose that connects to the pressure switch plugged?
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http://www.thehvacmedic.com/cgi-bin/forum/Blah.pl wrote:

Sometimes the inducer isn't up to speed and cause's nusiance tripping of the pressure switch. On this model, it must prove to the control board that it's in a open, then closed position upon inducer induction. If checking the flu pipe doesn't prove out, then measure the inducer performance by connecting a incline manometer to the pressure switch [BTW: it's actually a vacuum switch] and take a reading. If the reading isn't what's marked on the switch, suspect the inducer or a clogged hose. [Sometimes spiders crawl into the hose and plug it.]
--
Zyp



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