DEMAND DEFROST CONTROL (A108) DIAGNOSTIC LEDS
The state (Off, On, Flashing) of two LEDs on the demand defrost control (DS1 [Red] and DS2 [Green]) indicate diagnostics conditions that are described in table 10.
Table 10. Demand Defrost Control (A108) Diagnostic LEDs
DS1 and DS2 System Status, Fault and Lockout Codes
DS2 | DS1 | Type | Condition/Code | Possible Cause(s) | |
Green | Red | ||||
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No power (24V) to demand
OFF OFF Status Power problemdefrost control terminals R and C or demand defrost control failure.
Solution
1Check control transformer power (24V).
2If power is available to demand defrost con- trol and LED(s) do not light, replace demand defrost control.
Simultaneous | Status | Normal operation | ||
SLOW Flash | ||||
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Alternating SLOW | Status | 5−minute anti−short cycle delay | ||
Flash |
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Simultaneous | Fault | Ambient Sensor Problem | ||
FAST Flash | ||||
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Alternating |
| Fault | Coil Sensor Problem | |
FAST Flash | ||||
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ON | ON | Fault | Demand Defrost Control | |
Failure | ||||
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Unit operating normally or in | None required. |
standby mode. |
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Initial power up, safety trip, end of | None required (jumper TEST pins to override) |
room thermostat demand. |
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Sensor being detected open or shorted or out of temperature range. Demand defrost control will revert to time/temperature defrost operation. (System will still heat or cool).
Sensor being detected open or shorted or out of temperature range. Demand defrost control will not perform demand or time/temperature defrost operation. (System will still heat or cool).
Indicates that demand defrost control has internal component failure. Cycle 24VAC power to demand defrost control. If code does not clear, replace demand defrost control.
| SLOW |
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| 1 Restricted air flow over indoor or | 1 Remove any blockages or restrictions from | ||||||
OFF | Fault | Low Pressure Fault | coils and/or fans. Check indoor and outdoor | ||||||||
Flash | |||||||||||
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| outdoor coil. |
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| fan motor for proper current draws. | |||||
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| 2 Improper refrigerant charge in | 2 Check | system | charge using subcooling | ||||
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OFF | ON | Lockout | Low Pressure Lockout | system. |
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| 3 Improper | metering | device | 3 Check | system | operating pressures and | ||
SLOW |
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| installed or incorrect operation | compare to unit subcooling tables in this | ||||||
OFF | Fault | High Pressure Fault | of metering device. |
| instruction or located on unit access panel. | ||||||
Flash | 4 Incorrect |
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| 4 Make sure all pressure switches and sensors | ||||||
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| or | improper | sensor | ||||||
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| location | or | connection to | have secure connections to system to prevent | ||||
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ON | OFF | Lockout | High Pressure Lockout | system. |
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| refrigerant leaks or errors in pressure and | |||
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| temperature measurements. | |||||||
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SLOW | ON | Fault | Discharge Line Temperature | This code detects shorted sensor or high discharge temperatures. If the discharge | |||||||
Flash | Fault | line temperature exceeds a temperature of 285ºF (140ºC) during compressor | |||||||||
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| operation, the demand defrost control will de−energize the compressor contactor | |||||||
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FAST | ON | Lockout | Discharge Line Temperature | output (and the defrost output if active). The compressor will remain off until the | |||||||
Flash | Lockout | discharge temperature has dropped below 225ºF (107ºC). | |||||||||
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OFF | Fast | Fault | Discharge Sensor Fault | The demand defrost control detects open sensor or out of temperature sensor range. | |||||||
Flash | |||||||||||
This fault is detected by allowing the unit to run for 90 seconds before checking | |||||||||||
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| sensor resistance. If the sensor resistance is not within range after 90 seconds, the | |||||||
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Fast | OFF | Lockout | Discharge Sensor Lockout | demand defrost control will count one fault. After 5 faults, the demand defrost control | |||||||
Flash |
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(Each fault adds 1 strike to that code’s counter; 5 strikes per code = LOCKOUT)
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