Problem | Possible Cause | Corrective Action |
Suction pressure too | • Dirty or blocked evaporator coil | • Clean evaporator coil. |
low | • Dirty or blocked air filters | • Check filters and replace as needed. |
| • Low airflow | • Check for correct airflow setting. |
| • Low return air temperature | • Verify the return air temperature is not below |
|
| 20ºC (68°F). |
|
| • Check for short cycling of cold supply air. |
| • Low refrigerant charge | • Check subcooling and ensure it is at least |
| • Liquid line filter drier is blocked | |
| • Check filter drier for excessive pressure drop. | |
| • High evaporator superheat | • Check for proper superheat and TXV |
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| operation. |
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System short of | • Low refrigerant charge | • Check subcooling and ensure it is at least |
capacity | • Liquid line filter drier is blocked | |
| • Check filter drier for excessive pressure drop. | |
| • High evaporator superheat | • Check for proper superheat and TXV |
| • Insufficient air quantity across the | operation. |
| • Check for correct airflow and clean filters. | |
| evaporator coil |
|
| • Excessive outside air infiltration | • Reduce outside air infiltration. |
| • Lack of proper room vapor barrier | • Install vapor barrier materials on floor, walls, |
|
| and ceiling as needed. |
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|
Temperature control | • Excessive outside air infiltration | • Reduce outside air infiltration. |
not tight enough | • Lack of proper room vapor barrier | • Install vapor barrier materials on floor, walls, |
|
| and ceiling as needed. |
| • Cool/reheat setpoints not close | • Check cooling and reheat setpoints and |
| enough | deadbands. |
| • Reheat PID loop is not properly | • Tune the PID loop for accurate reheat |
| tuned | operation. |
| • Interstage delay is too large | • Reduce the interstage delay to allow quicker |
|
| response to temperature changes. |
| • Return air temperature does not | • Check for short cycling of cold supply air. |
| reflect actual room condition | • Check air distribution for deficiencies. |
|
| • Consider using remote sensor control. |
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| Note: Be certain to purchase the correct |
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| temperature and humidity probe. Check when |
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| ordering that your equipment is compatible. |
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Water carryover | • Dirt or oil residue on evaporator | • Clean the evaporator coil. |
| coil | • Check for correct airflow and clean filters. |
| • Insufficient air quantity across the | |
| evaporator coil | • Reduce airflow to specifications. |
| • Excessive airflow across the | |
| evaporator coil | • Clean condensate pan and drain line. |
| • Blockage in condensate pan or | |
| drain line | • Verify the return air temperature is not below |
| • Low return air temperature | |
|
| 20ºC (68ºF). |
|
| • Check for short cycling of cold supply air |
| • High return humidity | • Lower humidity setpoint. |
|
| • Check for short cycling of supply air |
| • Excessive outside air infiltration | • Reduce outside air infiltration. |
| • Lack of proper room vapor barrier | • Install vapor barrier materials on floor, walls, |
|
| and ceiling as needed. |
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NetworkAIR FM DX 60 Hz Operation, Maintenance, and Troubleshooting | 79 |