Upon arrival found downstairs system not heating. Turned system on and checked furnace in attic. Found that system was giving a low pressure switch fault. Found that the positive and negative pressure switch tubes were switched. Swapped tubes and tried to turn on system again. System did not come on. Tried to check wiring for pressure switched but couldn’t find a good enough diagram. Called tech support and they had me wire the switches correctly. Checked igniter and drain tubes for furnace all were clear. Turned system on and furnace came on. Cycled unit three times and tested second stage system is heating properly at this time.