Lennox Blower Replacement Kit Installation Instructions

Shipping and Packing List

Package 1 of 1 contains:

• 1-Blower assembly
• 3-Primary limit switches (S10)
• 1-Transformer bracket
• Bag assembly containing:
  • 3-Fuses and holders
  • 1-Wire harness
  • 1-Wiring diagram
  • Hardware

Ordered and shipped separately for J Volt Units:

• T4 Transformer

Installation Steps Overview

1. Open access panels. See Figure 1.
2. Disconnect B3 Modbus connection and PT6 connection (LGM only) in the blower section. See Figure 2.
3. Disconnect P48 in the controls area. See Figure 4.
4. Cut wire ties where necessary and pull P48 wiring harness from the control area into the blower section.
5. Use the handle on the blower assembly to slide the assembly out of the unit.
6. Note the heat exchanger dimples (tri-dimple or offset-dimple) to select the appropriate replacement limit switches.
7. Install the replacement blower assembly flanges into rails on the blower deck and secure with four screws.
8. Uncoil the P48 wiring harness secured to the replacement blower housing.
9. Route the P48 harness end through the unit to the control area.
10. Connect B3 Modbus and PT6 connections as shown in Figure 2.
11. Bundle harnesses and use wire ties to secure kit harnesses to unit harnesses.

Firmware Update

Required before proceeding:

1. Update the Unit Controller firmware to version 09.02.0320 or newer.
2. Set configuration ID 1, (7) System Blower Sub-Type, to “5” - Direct-Plus blower MODUS. Use the menu path: RTU MENU > SETUP > INSTALL.

Application

This kit replaces a 450mm blower with a 500mm blower. The 31A56 is used on Y-volt units and the 31A57 is used on G- & J-Volt units.

Replace Blower Motor

Important Note: Direct-drive motors may not stop immediately when power is interrupted to the Unit Controller. Always disconnect unit power before opening the blower compartment. The Controller's digital inputs must be used to shut down the blower. Refer to the Unit Controller manual for specific operation sequences.

1. Disconnect electrical power to the unit. Wait five minutes before continuing service procedures to allow internal capacitors time to fully discharge and avoid electrical shock.
2. Remove four screws securing the blower assembly to the unit. See Figure 5.
3. If the unit was equipped with a blower proving switch, remove the switch from the existing blower housing and attach it to the replacement blower assembly in the same manner.
4. For LGM Units Only: Disconnect the pressure tubing from the PT6 pressure sensor. Remove two screws and detach the sensor/bracket assembly (noting its orientation) from the existing blower housing. Install the sensor/bracket onto the replacement blower assembly and reattach the tubing.

Install New Limit Switch

Move the limit switch from the left side of the blower to the right side of the blower. See Figure 6.

1. Remove and retain screws securing the limit switch on the left side of the blower assembly. Discard the old limit switch.
2. Remove and retain screws securing the patch plate on the right side of the blower deck.
3. Place the patch plate over the opening left by the discarded switch on the left side of the blower. Secure with retained screws.
4. Select the replacement switch based on the heat exchanger type (see Figure 5 for heat exchanger dimples):
   • Tri-Dimple Heat Exchangers (See Figure 7):
     • Std. Heat (6 tubes; 150°F) - Part Number: 49L8901
     • Med. Heat (9 tubes; 175°F) - Part Number: 49L8601
     • High Heat (11 tubes; 185°F) - Part Number: 100847-10
   • Offset-Dimple Heat Exchangers (See Figure 8):
     • Std. Heat (6 tubes; 150°F) - Part Number: 100847-04
     • Med. Heat (9 tubes; 190°F) - Part Number: 100847-12
     • High Heat (11 tubes; 185°F) - Part Number: 100847-10
5. Install the selected switch on the right side of the blower and secure with retained screws.
6. Cut the wire ties securing the discarded switch. Route wires to the replacement switch on the right side of the blower and connect them to the terminals.

Install T4 Transformer (575 / J-Volt Only)

1. Install the bracket in the unit (provided in some units). Secure with provided hardware. See Figure 9.
2. Secure the transformer and fuses onto the bracket.

Connect Wiring

1. G-Volt Units: Connect the J48 power harness to P48 (previously routed from the replacement blower). See Figure 4.
2. J-Volt Units: Remove and discard the existing J48 harness routed to TB13. See Figure 4. Make kit harness connections as shown in Figure 10.

Safety Warnings and Cautions

⚠️ WARNING

To prevent serious injury or death:

1. Lock-out/tag-out procedures must be followed before performing maintenance.
2. If system power is required (e.g., for smoke detector maintenance), disable power to the blower, remove the fan belt where applicable, and ensure all controllers and thermostats are set to the “OFF” position before performing maintenance.
3. Always keep hands, hair, clothing, jewelry, tools, etc., away from moving parts.

General Installation Warning: Improper installation, adjustment, alteration, service, or maintenance can cause property damage, personal injury, or loss of life. Installation and service must be performed by a licensed professional installer (or equivalent), service agency, or the gas supplier.

⚠️ CAUTION

As with any mechanical equipment, personal injury can result from contact with sharp sheet metal edges. Be careful when handling this equipment.

Diagram Descriptions

Figure 1: Unit Access Panels

Figure 2: Blower Section Wiring

Figure 3: PT6 Sensor for LGM Units

Figure 4: Control Area Wiring

Figure 5: Blower Assembly Removal

Figure 6: S10 Limit Switch Installation

Figure 7: Tri-Dimple Heat Exchanger

Figure 8: Offset-Dimple Heat Exchanger

Figure 9: T4 Transformer Installation

Figure 10: J-Volt Harness Connections