need some help this furnace has been looked at by 2 other companys and about 4 of my co-workers and know me. the furnace is a carrier infinity model 58vca100 original complaint was 44 code. i found 44 code due to fan speed set higher than 1300 cfm on circuit board settings adjusted and went away. Then found furnace would on call for heat run high fire about 45 sec then ramp down to low fire then low pressure switch chatters and furnace goes to 32 code flashes that code couple minutes then resets to high fire. switch makes at .60 and breaks at .43 Sometimes when ramps down read .45 between collector box and switch and runs fine other times it drops down to .35 and opens switch. checked flue,intake pipes, drainlines, inducer wheel. any other ideas???? Has a new secondary heat exchanger, checked switch hosesand port on collector box. not sure what water column should be on low fire but running .45 seems close to drop out point. thought maybe inducer ramping to low but hate to replace it and be wrong a very exspensive part.