Have a customer with a coleman evcon mobile home furnace L.P. gas, m/n dgat056bdf s/n980908580, i am the 3d person to work on this furnace supposedly tripping on fault code 3 pressure switch not proving at night only, during the day it works fine. First person replaced the pressure switch, original was .20"wc the one he installed is a .10"wc switch, customer said the furnace still trips the same error at night. Second person never cleaned or checked anything never went on the roof told the customer the heat exchanger was bad and the roof jack was no good. I spent 2 hours today checking everything, checked the heat exchanger from inside the combustion chamber with flashlight and mirror and also a borescope camera, checked from above after removing the blower, can find no crack/hole in the heat exchanger, went on the roof pulled the top off the roof jack thinking that had rotted and plugged the top of the exchanger, all looked good from up there, pulled the inducer assembly off and checked the wheel and the combustion air inlet for bees, no problems found, resealed the inducer assembly which someone else had removed and left a screw out and never scraped off the old caulk and resealed. I ran the furnace, cycled it on at least 12 times no problems at all, even put in the original pressure switch, no problems, measured the draft at the inducer -.18"wc before ignition, -.16"wc after ignition and -.13"wc after the blower starts. I can find no reason for this to drop out the pressure switch, possibly sealing the inducer housing will solve the problem, but has anyone else had issues with these coleman furnaces not proving pressure switches?? I was sure I would find a bad roof jack or bad heat exchanger but no luck. I have changed a lot of these furnaces every customer that has one has not been happy with the coleman furnaces and a lot of them have had issues with the pressure switch.