Brand: Lennox
Category: Home HVAC System
Manual Type:
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Manual for 4HP17L - Troubleshooting and error codes + PDF Download
Uploaded: April 7, 2025, 8:13 p.m.
Warranty Summary
Warranty information is not mentioned in this installation manual.
Cooling Mode: Operate unit for at least 10 minutes. Measure liquid service pressure and liquid line temperature. Calculate subcooling and compare with the table on the central box cover. Adjust refrigerant if needed.
Heating Mode: Check charge if the ambient temperature is below 60°F and indoor temperature is between 65°F and 75°F. Follow the same steps as cooling mode and compare with heating mode subcooling range.
Pressure Switch Connections: Unit uses automatic reset pressure switches for low and high pressure.
Demand Defrost System: System measures differential temperatures to detect ice build-up and initiates defrost cycles as needed.
Troubleshooting and error codes
| DS2 Green | DS1 Red | Type | Condition / Code | Possible Cause(s) | Solution |
|---|---|---|---|---|---|
| OFF | OFF | Status | Power Problem | No power (24V) to control board terminals R and C or control board failure. | 1. Check control transformer power (24V). 2. If power is available to control board and LED(s) do not light, replace control board. |
| Simultaneous SLOW Flash | Status | Status | Normal operation | Unit operating normally or in standby mode. | None required. |
| Alternating SLOW Flash | Status | Status | 5-minute anti-short cycle delay | Initial power up, safety trip, end of room thermostat demand. | None required (jumper TEST pins to override) |
| Simultaneous FAST Flash | Fault | Fault | Ambient Sensor Problem | Sensor being detected open or shorted or out of temperature range. Control board will revert to time/temperature defrost operation. (System will still heat or cool). | Sensor being detected open or shorted or out of temperature range. Control board will revert to time/temperature defrost operation. (System will still heat or cool). |
| Alternating FAST Flash | Fault | Fault | Coil Sensor Problem | Sensor being detected open or shorted or out of temperature range. Control board will not perform demand or time/temperature defrost operation. (System will still heat or cool.) | Sensor being detected open or shorted or out of temperature range. Control board will not perform demand or time/temperature defrost operation. (System will still heat or cool.) |
| ON | ON | Fault | Demand Defrost Control Failure | Indicates that demand defrost control has internal component failure. Cycle 24VAC power to control board. If code does not clear, replace control board. | Indicates that demand defrost control has internal component failure. Cycle 24VAC power to control board. If code does not clear, replace control board. |
| OFF | SLOW Flash | Fault | Low Pressure Fault | • Restricted air flow over indoor or outdoor coil. • Improper refrigerant charge in system. | • Remove any blockages or restrictions from coils and/or fans. Check indoor and outdoor fan motor for proper current draws. • Check system charge using subcooling method. |
| OFF | ON | Lockout | Low Pressure Lockout | Improper metering device installed or incorrect operation of metering device. | Check system operating pressures and compare to unit subcooling tables located on unit access panel. |
| SLOW Flash | OFF | Fault | High Pressure Fault | ||
| ON | OFF | Lockout | High Pressure Lockout | Incorrect or improper sensor location or connection to system. | Make sure all pressure switches and sensors have secure connections to system to prevent refrigerant leaks or errors in pressure and temperature measurements. |
Troubleshooting and error codes
| DS2 Green | DS1 Red | Type | Condition / Code | Possible Cause(s) | Solution |
|---|---|---|---|---|---|
| OFF | OFF | Status | Power Problem | No power (24V) to control board terminals R and C or control board failure. | 1. Check control transformer power (24V). 2. If power is available to control board and LED(s) do not light, replace control board. |
| Simultaneous SLOW Flash | Status | Status | Normal operation | Unit operating normally or in standby mode. | None required. |
| Alternating SLOW Flash | Status | Status | 5-minute anti-short cycle delay | Initial power up, safety trip, end of room thermostat demand. | None required (jumper TEST pins to override) |
| Simultaneous FAST Flash | Fault | Fault | Ambient Sensor Problem | Sensor being detected open or shorted or out of temperature range. Control board will revert to time/temperature defrost operation. (System will still heat or cool). | Sensor being detected open or shorted or out of temperature range. Control board will revert to time/temperature defrost operation. (System will still heat or cool). |
| Alternating FAST Flash | Fault | Fault | Coil Sensor Problem | Sensor being detected open or shorted or out of temperature range. Control board will not perform demand or time/temperature defrost operation. (System will still heat or cool.) | Sensor being detected open or shorted or out of temperature range. Control board will not perform demand or time/temperature defrost operation. (System will still heat or cool.) |
| ON | ON | Fault | Demand Defrost Control Failure | Indicates that demand defrost control has internal component failure. Cycle 24VAC power to control board. If code does not clear, replace control board. | Indicates that demand defrost control has internal component failure. Cycle 24VAC power to control board. If code does not clear, replace control board. |
| OFF | SLOW Flash | Fault | Low Pressure Fault | • Restricted air flow over indoor or outdoor coil. • Improper refrigerant charge in system. | • Remove any blockages or restrictions from coils and/or fans. Check indoor and outdoor fan motor for proper current draws. • Check system charge using subcooling method. |
| OFF | ON | Lockout | Low Pressure Lockout | Improper metering device installed or incorrect operation of metering device. | Check system operating pressures and compare to unit subcooling tables located on unit access panel. |
| SLOW Flash | OFF | Fault | High Pressure Fault | ||
| ON | OFF | Lockout | High Pressure Lockout | Incorrect or improper sensor location or connection to system. | Make sure all pressure switches and sensors have secure connections to system to prevent refrigerant leaks or errors in pressure and temperature measurements. |