Lennox Low Ambient Control Kit LB-101123B Installation Instructions
For Single Outdoor Fan Heat Pump Units with R410A Refrigerant
Shipping & Packing List
Package 1 of 1 contains:
- Low ambient pressure switch assembly (S11 - part #83L6001)
- Relay (K58 - part #37H9601)
- 4 x 20" Lengths of wire (with 3/16" Female quick connects on one end)
- 4 x Wire nuts
- 2 x #10-16 X 5/8" S.D.S.T. screws
- 1 x Schrader depressor tee with seal cap
⚠️ IMPORTANT
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 qualified installer or service agency.
Application
The low ambient control pressure switch (S11) cycles the outdoor fan, allowing continuous compressor operation during a cooling demand. This intermittent outdoor fan operation maintains a minimum pressure differential across the expansion device as ambient temperature drops, reducing capacity losses during low ambient conditions. This kit is designed for use in ambient temperatures no lower than 30°F (-1°C), unless otherwise noted in the Engineering Handbook. It is suitable only for single fan heat pump units in R410A refrigerant applications.
ℹ️ NOTE: This kit may be applied in expansion valve systems only. It is not suitable for systems using capillary tube metering devices.
System must include a crankcase heater and a freezestat for low ambient operation. Add external belly-band crankcase heater and freezestat before continuing. Refer to Tables 1 and 2. See Figure 1 for freezestat wiring.
Installation
- Turn off electrical power to the unit.
- Remove compressor compartment access panel, if applicable.
- Install the provided low ambient pressure switch on the open port (no valve core) of the provided tee fitting. ℹ️ NOTE: Pressure switch must be installed before the tee is installed to avoid refrigerant loss.
- Install the tee fitting on the heat pump liquid line service port.
- Install the cap on the valve core port and tighten to 6 to 8 ft.-lbs.
- Route pressure switch wires into the control box and connect per the applicable unit wiring diagram.
- Use the two provided screws to mount the K58 relay in the control box.
- Wire in the K58 relay. See Figure 1.
Wire Connections
The low ambient control pressure switch (S11) and K58 N.C. (terminals 1 and 7) are wired in series with the outdoor fan relay, which is mounted on the defrost board. Wire the K58 coil (terminals A & B) in parallel with the reversing valve terminals (L1) on the defrost board.
Switch Settings
The provided low ambient pressure switch is factory set for 450 psig (3100 kPa) cut-in and 240 psig (1600 kPa) cut-out. This switch is not adjustable.
Diagrams and Tables
Figure 1: Typical Field Wiring Diagram
This diagram illustrates the typical field wiring for the Low Ambient Control Pressure Switch and K58 Relay. It shows connections to the compressor, dual capacitor, contactor, fan, and crankcase heater. The wiring includes the pressure switch (S11) and K58 normally closed contacts (terminals 1 and 7) in series with the outdoor fan relay on the defrost board. The K58 coil (terminals A & B) is shown wired in parallel with the reversing valve terminals (L1) on the defrost board. The diagram also indicates typical crankcase heater wiring.
Table 1: Crankcase Heaters for Units with Scroll Compressors
| Scroll Compressors | Volts | Watts | Manufacturer's Part Number | Power Leads | Dimensions | Lennox Part Number |
|---|---|---|---|---|---|---|
| 1-1/2 to 3 ton (ZR18K-ZR42K) | 240 | 40 | 018-0041-00 | 18ga 40" | 20" to 26" | 18K2001 |
| 480 | 40 | 018-0041-01 | 18ga 21-1/2" | 20" to 26" | 49K1101 | |
| 575 | 40 | 018-0041-02 | 18ga 21-1/2" | 20" to 26" | 49K1201 | |
| 4 to 7-1/2 ton (ZR46K-ZR72K) | 240 | 70 | 018-0043-00 | 18ga 30" | 21-1/8" to 30" | 31J2001 |
| 480 | 70 | 018-0043-01 | 18ga 30" | 21-1/8" to 30" | 31J2101 | |
| 575 | 70 | 018-0043-02 | 18ga 30" | 21-1/8" to 30" | 42J8501 | |
| 1-1/2 to 3 ton | 240 | 40 | CH196 | 18ga 40" | 21" to 26-1/2" | 90P12 |
ℹ️ NOTE: Any 208/240 volt 40 watt heater can be substituted by Tutco 67K9001 70 watt heater. Any 480 volt 40 watt heater can be substituted by Tutco 67K8901 70 watt heater.
Table 2: Freezestat Selection
| Tubing Size | Wire Length | Wire Gauge | Lennox Part Number |
|---|---|---|---|
| 3/8" | 90 13/16" | 18 | 93G35 |
| 1/2" | 140 13/16" | 18 | 39H29 |
| 5/8" | 36 1/2" | 18 | 50A93 |
ℹ️ NOTE: Use ONLY expansion valve metering devices on units with low ambient kits.
Figure 2: Thermostat Designations and Wiring
This diagram illustrates thermostat designations and wiring connections between the thermostat, indoor unit, and outdoor unit. It includes terminals for power, common, auxiliary heat (W1, W2), indoor blower (G), reversing valve (O), and compressor (Y1). It also shows the freezestat connection.
Operational Checkout
Cooling Mode
To initiate cooling mode, set the room thermostat to call for cooling. The defrost board will receive a Y and O signal from the thermostat. The O signal energizes the reversing valve and the K58 relay coil, causing K58-1 contacts to open. The Y signal passes through the freezestat to Y1 on the defrost board, then to the HI-PS terminals, through the high pressure switch, and back to the other HI-PS terminal. The signal returns from the defrost board on the Y terminal, energizing the compressor contactor coil and starting the compressor. The outdoor fan motor remains OFF until the liquid line pressure reaches the low ambient pressure switch setting (450 psig - 3100 kPa). When the liquid line pressure rises above 450 psig (3100 kPa), the outdoor fan cycles ON. When the liquid line pressure falls below 240 psig (1600 kPa), the outdoor fan cycles OFF.
ℹ️ NOTE: The outdoor fan motor is cycled by the low ambient pressure switch and K159 relay. During a cooling call, when liquid line pressure rises above 450 psig (3100 kPa), the outdoor fan cycles ON. When liquid line pressure falls below 240 psig (1600 kPa), the outdoor fan cycles OFF.
Heating Mode
To initiate heating mode, set the room thermostat to call for heating. The defrost board will receive a Y signal from the thermostat. The O signal from the thermostat is not energized, so the K58 relay coil is not energized. Contacts K58-1 remain closed. The Y signal passes through the freezestat to Y1 on the defrost board. The signal goes into the defrost board to the HI-PS terminals, out to the high pressure switch, and back to the other HI-PS terminal. The signal returns from the defrost board on the Y terminal, energizing the compressor contactor coil and starting the compressor. The K58-1 relay contacts (normally closed) prevent the low ambient pressure switch from interrupting the outdoor fan motor operation during heating mode.
