HVACopediaLennox · Heat pump
Green & Red simultaneous SLOW flash Normal operation or standby
What the display is showing
Both LEDs on the demand defrost control (DS2 green, DS1 red) blink slowly together. This is the healthy state: the unit is running normally or waiting for a thermostat call. No action is needed.
Applies to: Lennox EL16KP1 (Elite) and ML14KP1 (Merit) R-454B heat pumps, sizes -018 to -060, demand defrost control A108 (CMC1)
Settings for these units
Outdoor unit clearances · Lennox EL16KP1
| Location | Clearance |
|---|---|
| Service side (one side next to control box) | 30 in. (762 mm) |
| One of the other three sides | 36 in. (914 mm) |
| One of the remaining two sides | 12 in. (305 mm) |
| Last side | 6 in. (152 mm) |
| Between two units | 24 in. (610 mm) |
| Top | 48 in. (1219 mm) |
| Above roof surface (roof mount) | 6 in. (152 mm) minimum |
Increase clearances where snow/ice can fall on the unit or air can recirculate (decks, tight spaces).
Wind barrier, if used, 24 in. (610 mm) from the unit.
Outdoor unit clearances · Lennox ML14KP1
| Location | Clearance |
|---|---|
| Service side (one side next to control box) | 24 in. (610 mm) |
| One of the other three sides | 36 in. (914 mm) |
| One of the remaining two sides | 12 in. (305 mm) |
| Last side | 6 in. (152 mm) |
| Top | 48 in. (1219 mm) |
| Multi-unit, between units | 12 in. (305 mm) minimum [18 in. (457 mm) recommended] or 24 in. (610 mm) depending on layout |
| Multi-unit service side | 24 in. (610 mm) recommended |
| Above roof surface (roof mount) | 6 in. (152 mm) minimum |
Multi-unit spacing (A/B) depends on single row, wall or multiple rows layout - see figure on p.7.
Increase clearances where snow/ice can fall on the unit or air can recirculate.
Models that show this code
14 models in Lennox EL16KP1, Lennox ML14KP1
Other codes on the same units
- Amber light Emergency heat indicator (thermostat)
- Green & Red alternating FAST flash Coil (defrost) sensor problem
- Green & Red alternating SLOW flash 5-minute anti-short-cycle delay
- Green & Red simultaneous FAST flash Ambient (outdoor air) sensor problem
- Green FAST flash / Red OFF Discharge sensor lockout
- Green FAST flash / Red ON Discharge line temperature lockout
- Green OFF / Red FAST flash Discharge sensor fault
- Green OFF / Red OFF No power to the demand defrost control
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Source: Lennox EL16KP1 Unit Information 100195 / ML14KP1 Unit Information 100108, Table 4 Demand Defrost Control (A108) Diagnostic LEDs, p.32. Summarized in our own words; check the original manual for your model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.