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01/11
*2P0111*
506475−01
*P506475-01*
E 2010 Lennox Industries Inc.
Dallas, Texas, USA
AIR FLOW
DOWNFLOW
INSTALLATION
INSTRUCTIONS
ML193DF
MERIT
®
SERIES GAS FURNACE
DOWNFLOW AIR DISCHARGE
506475−01
01/2011
Supersedes 10/2010
THIS MANUAL MUST BE LEFT WITH THE
HOMEOWNER FOR FUTURE REFERENCE
This is a safety alert symbol and should never be ignored.
When you see this symbol on labels or in manuals, be alert
to the potential for personal injury or death.
CAUTION
As with any mechanical equipment, personal injury
can result from contact with sharp sheet metal
edges. Be careful when you handle this equipment.
WARNING
Improper installation, adjustment, alteration, service
or maintenance can cause property damage, person-
al injury or loss of life. Installation and service must
be performed by a licensed professional installer (or
equivalent), service agency or the gas supplier.
Table of Contents
Unit Dimensions 2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ML193DF Parts Arrangement 3. . . . . . . . . . . . . . . . . . . . .
ML193DF Gas Furnace 4. . . . . . . . . . . . . . . . . . . . . . . . . .
Shipping and Packing List 4. . . . . . . . . . . . . . . . . . . . . . . .
Safety Information 4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Use of Furnace as a Construction Heater 5. . . . . . . . . . .
General 6. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Combustion, Dilution and Ventilation Air 6. . . . . . . . . . . .
Setting Equipment 9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Filters 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Duct System 12. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Pipe and Fittings Specifications 12. . . . . . . . . . . . . . . . . . .
Joint Cementing Procedure 14. . . . . . . . . . . . . . . . . . . . . .
Venting Practices 14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Vent Piping Guidelines 15. . . . . . . . . . . . . . . . . . . . . . . . . .
Gas Piping 30. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electrical 32. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unit Start Up 36. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Gas Pressure Measurement 38. . . . . . . . . . . . . . . . . . . . .
Proper Combustion 38. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High Altitude 38. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Testing Non Direct Appliances for Proper Air 39. . . . . . .
Other Unit Adjustments 40. . . . . . . . . . . . . . . . . . . . . . . . . .
Blower Motor Performance 41. . . . . . . . . . . . . . . . . . . . . . .
Service 42. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Planned Service 44. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Integrated Control Diagnostic Codes 44. . . . . . . . . . . . . .
Troubleshooting 45. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Repair Parts List 49. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Start Up Checklist 50. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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