Working on the Lennox modulating furnace with the communicating thermostat and it been locking up with calibration issue for the low pressure switch.the model number of the unit is SL98UH090v36v-01.checked the vent and air intake both are clear.any thoughts?
How does the drainage system look?
Lennox has had their share of pressure switch problems. I would try replacing that.
The manual says for upflow installations the P-Trap can be installed on either side of the furnace, but I have read where installing it on the left side can cause problems.
check the pressure ports themselves, had more than a fair share of those plug up with crap, I usually take my tiny screwdriver and poke it through the port a few times to clear up any crap in there. I have also had an instance where the board itself was just giving that false error and changing the board fixed it
Dont forget that on this furnace there are actually two holes behind the Ventor Motor on the collector box. There is the big huge hole that you cant miss and a tiny one that can be missed easily and can get plugged up with crap.
SLP98 is pretty known for having very crappy pressure switches. They've released a (hopefully) improved version. I think they just changed the location of the port for one of the tubings there.