Lennox ML193UH090XE48C User Manual

Page 16
TABLE 7
Pressure Switch Troubleshooting Guide
Problem Corrective Action
Pressure switch stuck closed
Check that the pressure switch is open without the combustion air inducer operat
ing. Replace if defective.
Pressure switch does not close due to
obstruction in vent pipe.
Check for restricted vent. Remove all blockage.
Check for proper vent sizing. See table 12.
Pressure switch does not close due to
incorrect routing of the pressure
switch tubing.
Check that the pressure switch tubing is correctly routed. Correctly route pressure
witch line.
Pressure switch does not close due to
obstructions in the pressure switch
line.
Remove any obstructions from the the pressure switch line and/or taps
Pressure switch tubing damaged. Check pressure switch tubing for leaks. Replace damaged tubing if necessary.
Condensate in pressure switch tubing. Check pressure switch tubing for condensate. Remove condensate from tubing.
Pressure switch does not close due to
a low differential pressure across the
pressure switch.
Check the differential pressure across the pressure switch.
Check for restricted inlet vent. Remove all blockage.
Check for proper vent sizing and run length. See table12.
Wrong pressure switch installed in the
unit, or pressure switch is out of cal
ibration
Check that the correct pressure switch is installed in the unit. Replace pressure
switch if necessary.
Miswiring of furnace or improper con
nections at pressure switch.
Check for correct wiring and loose connections. Correct wiring and/or replace any
loose connections.
Pressure switch failure.
If all the above modes of failure have been checked, the pressure switch may have
failed. Replace pressure switch and determine if unit will operate.
Damaged condensate trap. Check trap for any cracks or damage and replace if necessary.
Cold end header box does not drain
properly.
Check that the furnace is set properly with a slight tilt (0 - 1/2”) towards the front
if necessary. See furnace installation instruction.
Air leakage around the combustion air
inducer gasket.
Check gasket and replace if necessary.
Air leakage around the cold end head
er box gasket.
Check gasket and replace if necessary.
Damaged cold end header box tubing. Check tubing and replace if necessary.

Lennox ML193UH090XE48C Specifications

General

Brand	Lennox
Model	ML193UH090XE48C
Category	Furnace
Language	English