Quick answer: Maintenance protects five things: airflow (filters, fans), heat transfer (coils, rotor), drainage (pan, hose, pump), sensor accuracy, and electrical and control reliability. Check drains and alarms often, clean or replace filters monthly (weekly on dusty sites), clean coils every 6–12 months, verify humidity sensors yearly, and record water collected and power used so you can spot falling performance before the space gets humid. Always isolate power before opening a unit.
Quick answer
- Weekly: drain, filter condition, alarms, unusual noise.
- Monthly: clean or replace filters; check fans and drain pump.
- Every 6–12 months: clean coils; check electrical connections; verify sensors.
Checklist by interval
| Interval | Task | Refrigerant units | Desiccant units |
|---|---|---|---|
| Daily / per shift (critical sites) | Check zone RH on display or BMS; confirm unit running; no alarms | ✓ | ✓ |
| Weekly | Inspect filter; check drain flow or pump; listen for unusual noise; check for frost on coil (refrigerant) | ✓ | ✓ |
| Monthly | Clean or replace filters; clean drain pan; test condensate pump and overflow switch | ✓ | ✓ (both air streams) |
| Quarterly | Check fan belts and bearings; inspect reactivation duct and exhaust (desiccant); check door seals of the space | ✓ | ✓ |
| Every 6–12 months | Clean evaporator and condenser coils; check refrigerant circuit performance (technician); tighten electrical connections; verify humidity sensor against a reference | ✓ | — |
| Every 12 months | Inspect rotor face and seals; check reactivation heater and temperature; verify sensors | — | ✓ |
| After water damage jobs (portable units) | Clean filters and coils; flush drain; check for contamination | ✓ | ✓ |
Safety: isolate and lock off power before opening panels, following electrical safety rules such as OSHA 1910.333 in the US (OSHA).
Record a baseline at commissioning
Capacity usually falls slowly, so nobody notices until there's a complaint. A baseline taken at handover lets you catch it early:
| Measurement | Where |
|---|---|
| Inlet temperature and RH | At the unit inlet |
| Outlet temperature and RH | At the outlet |
| Airflow | Measured, not assumed |
| Power input (kW) | At the supply |
| Water collected per running hour | Over a measured period |
| Filter pressure drop (clean) | Across the filter |
| Refrigerant pressures and temperatures | By a qualified technician |
| Settings | Setpoint, deadband, fan mode, schedule |
Water per running hour = water collected ÷ running hours. Judge filters by pressure drop against the clean baseline, not by how they look.
Performance check: is it still removing water?
Once a month in the humid season, record:
- room temperature and RH at the unit inlet;
- water collected per running hour (or pump run time);
- kWh used over the same period;
- filter pressure drop.
Compare with the baseline at a similar inlet condition. A steady fall points to dirt, airflow problems, refrigerant loss or, for desiccant units, rotor or heater issues; see do dehumidifiers lose efficiency over time.
Humidity rising: equipment or load?
| Observation | Points to |
|---|---|
| Water per hour down at the same inlet condition | Equipment (filter, coil, refrigerant, airflow) |
| Water per hour up, humidity still high | Load increased (doors, process, weather) |
| Unit not running when it should | Controls, setpoint, sensor |
| Water collected but not leaving | Drain fault |
The fixes differ: cleaning won't help if the load grew, and adding a unit won't help a fouled coil.
Set intervals by condition
| Factor | Effect on interval |
|---|---|
| Running hours | More hours, more frequent |
| Dust, fibres, oil mist | Filters and coils more often |
| Corrosive air (coastal, chemical) | Coil and electrical checks more often |
| Critical application | Shorter intervals, spares on site |
Refrigerant work, including leak checks for R290 units under flammable-refrigerant procedures, is for qualified technicians.
Low water collection: quick troubleshooting
| Symptom | Check |
|---|---|
| Little water, room humid | Filter, coil frost, fan speed, refrigerant (technician), room too cold |
| Little water, room already dry | Normal; unit is reaching setpoint |
| Frost on coil above 15 °C room temperature | Low airflow or refrigerant problem |
| Water on the floor | Blocked drain, pump fault, overflow |
| Desiccant unit, humid process air | Heater fault, rotor not turning, filter blocked, seal leaks |
Maintenance log template
| Date | Unit | Running hours | Inlet T / RH | Water per hour | kWh | Filter ΔP | Drain | Alarms | Notes / technician |
|---|---|---|---|---|---|---|---|---|---|
When to call the supplier
- Capacity falls despite clean filters and coils.
- Compressor short-cycles or trips.
- Refrigerant leak suspected (oily residue, ice on coils).
- Repeated electrical or control faults.
- Desiccant rotor damage or heater failure.
Keep the model and serial number, recent log entries and photos ready. For our units, our team can advise on spare parts and service; see our industrial dehumidifiers and desiccant dehumidifiers.
FAQ
Frequently asked questions
How often should a commercial dehumidifier be serviced?
Filters monthly (or weekly on dusty sites), coils every 6–12 months, and a full technical check yearly.
How do I know if my dehumidifier is losing capacity?
Compare water collected per running hour with the commissioning baseline at a similar inlet condition.
How do I clean a dehumidifier coil?
Isolate power, remove panels, use a suitable coil cleaner and soft brush or low-pressure rinse as the manufacturer allows, and let it dry before restarting.
Why is my dehumidifier collecting less water?
Dirty filter or coil, low airflow, frost, refrigerant loss, or simply a drier or cooler room.
Sources
- OSHA 29 CFR 1910.333, Selection and use of work practices.
- NIST, Humidity measurement and calibration.
- ASHRAE, Fundamentals of psychrometrics.
- ASHRAE Guideline 0, The Commissioning Process.
