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A cabinet cooling controller can show a normal temperature while a drive still trips on overtemperature. Before ordering a larger cooler, check what the alarm measures and where the temperature sensor is located.
SUWI’s starting point is to separate three possible causes: more heat than the calculation allowed for, insufficient cooling at the actual operating conditions, or poor airflow to the affected device. Each requires a different correction.
The checks below focus on finding which assumption no longer matches the installed cabinet. For the underlying thermal principles, see Why Cabinet Cooling Has Become a Critical Engineering Decision and Understanding Heat Generation Inside Electrical Cabinets.
Start with the symptom you can observe. Use the table to choose a first check. A symptom can have several causes; the linked section helps narrow the investigation.
| Observed symptom | First check | Read next |
|---|---|---|
| The cooling controller reads normally, but one drive overheats. | Check the drive alarm definition and its inlet air temperature; inspect local recirculation. | Section 4: Airflow |
| Cabinet temperature rises during sustained high-load production. | Compare simultaneous component losses and available cooling capacity at the actual temperatures. | Section 1: Heat load |
| The cabinet worked previously, but temperatures have gradually risen. | Compare filter, heat-transfer surface and airflow condition with the commissioning baseline. | Section 6: Maintenance |
| The cooling unit repeatedly starts and stops. | Compare temperature and cooling demand with controller settings, door-switch status and alarms. | Section 5: Capacity and control |
| Water appears after door opening or during cooling. | Locate the moisture and distinguish cold-surface condensation, external ingress and drainage faults. | Section 3: Environment |
Start the heat-load review with the machine operating state that produced the alarm. Record which drives, heaters and auxiliary devices were running together, then compare their losses with the calculation inputs. If the alarm occurs during sustained high-load production, check whether the calculation used that operating state. Standby or average-load losses may understate the heat generated during the fault period. Include surface heat transfer and solar exposure where applicable; heat passing through the enclosure wall can be a gain or a loss, depending on the temperature difference.
A common error is to count only the most obvious heat sources, such as a large variable frequency drive (VFD) or transformer. Smaller devices are often omitted: PLC racks, I/O modules, industrial power supplies, servo amplifiers, managed switches, safety controllers, contactors, HMIs, industrial PCs, and UPS systems. Individually, their losses may appear minor; in a dense cabinet, the combined load can consume a substantial part of the cooling margin.
Do not use equipment nameplate power as though it were heat dissipation. What matters is the component's power loss under the relevant duty cycle. For a drive, that means evaluating efficiency and operating load rather than assigning the full motor rating as cabinet heat. Conversely, using an unrealistically light average load can understate the heat produced during sustained high-output operation.
Another mistake is relying on rules of thumb without validating the finished machine. Engineering estimates are appropriate during concept development, but commissioning should include temperature measurements under representative production conditions. Record ambient temperature, cabinet inlet and outlet air temperatures, internal temperatures near critical devices, and machine operating state. Temporary data logging is much more useful than a single handheld reading taken with the enclosure door open.
For a structured calculation method and the data required from component suppliers, see Cabinet Heat Load Calculation Guide.
Cooling technologies are not interchangeable. The correct choice depends on heat load, required internal temperature, ambient temperature, enclosure protection needs, available installation space, and lifecycle constraints.
Filter fans are efficient and economical when ambient air is cool and sufficiently clean. They remove heat by exchanging cabinet air with the surrounding air, so they cannot cool the enclosure below ambient temperature. Their performance also falls as filters become loaded or airflow meets resistance from crowded components and poorly sized outlet filters.
Air-to-air heat exchangers keep internal and external air circuits separate, helping preserve enclosure protection against dust and contaminants. They are useful when ambient air is cooler than the desired cabinet temperature, but their heat-transfer capability declines as the temperature difference narrows. Specifying one where ambient temperature can approach or exceed the internal setpoint leaves little or no usable cooling potential.
Enclosure air conditioners can cool below ambient temperature and are appropriate for higher heat loads or hot industrial spaces. However, refrigeration adds energy consumption, condensate considerations, and maintenance requirements. A low-load cabinet in a clean, cool plant may not need compressor-based cooling. At the other extreme, a high-density drive cabinet may exceed the capability of ventilation even when the plant feels comfortable at operator level.
Advanced options—including variable-speed, hybrid, and connected cooling systems—can improve part-load efficiency and diagnostics, but they do not correct an inaccurate thermal model or poor installation. Start with the application, not the technology label. A useful comparison framework is provided in Choosing the Right Cabinet Cooling Method, with more detailed comparisons in Filter Fan vs Enclosure Air Conditioner and Air-to-Air Heat Exchanger Guide.
An enclosure cooling system interacts continuously with its surroundings. A solution that performs well in a clean assembly area may fail quickly beside a machining center, welding cell, washdown line, or outdoor process skid.
Dust and fibers load filters and heat-transfer surfaces, increasing airflow resistance and reducing available heat removal. A running fan does not prove that sufficient air is moving. Inspect the inlet and outlet filters together and compare airflow or pressure measurements with the clean-system baseline where available. Do not infer motor loading from blockage alone; the response depends on the fan and its controls. Oil mist can bind dust to filters and condenser surfaces, so a superficial visual check may miss a restricted air path.
High ambient temperature reduces the temperature difference available to ventilation and air-to-air heat exchangers. It also changes the effective capacity of an enclosure air conditioner. Selection must therefore be based on rated performance at the expected operating point—not only on a headline capacity measured under different conditions.
Condensation occurs when a surface is colder than the dew point of the air touching it. The cabinet controller reading alone cannot establish that every internal surface is above the dew point. If moisture appears after door opening, record temperature and humidity and inspect where it forms: cold-air discharge areas, cable entries or the condensate route. Separate moisture arriving from outside, condensation on cold surfaces and a drainage fault before changing the setpoint. Check the selected unit’s condensate instructions.
Outdoor cabinets require additional checks for solar radiation, rain, wind-driven dust, corrosion, seasonal temperature range, UV exposure, and low-temperature operation. A cooling unit approved only for protected indoor use should not be assumed suitable outdoors. See Outdoor Electrical Cabinet Cooling for the additional design inputs required in exposed installations.
If one drive reports overtemperature while the cooling controller shows a normal reading, check the air entering that drive before increasing cooling capacity. Record the drive inlet temperature, cooling-unit supply and return temperatures, and machine load over the same operating cycle. The controller measures conditions at its sensor, not the temperature at every device. Also check the drive alarm definition: an internal heatsink alarm is not the same measurement as cabinet air temperature.
Measure these locations over the same production cycle:
Compare against the right limit. Use the affected device’s permitted inlet air temperature and any relevant derating conditions. Use the exact cooling model’s performance data at the measured external and internal temperatures. A supply-to-return temperature difference alone does not establish delivered cooling capacity; airflow also matters. Thermal imaging can locate hot surfaces but does not measure air temperature.
Air must have a defined path from supply to return. Cable ducts, wire bundles, mounting plates, shelves, and densely installed modules can create short circuits in that path: cooled air returns to the cooling unit without reaching the heat-producing components. Recirculating hot discharge air through a device produces the opposite problem and can cause local derating even when total cooling capacity is adequate.
Component arrangement should support the thermal design. Place heat-sensitive PLCs, communication equipment, and control electronics away from concentrated heat sources where practical. Maintain the clearances specified by device manufacturers, especially above and below VFDs and servo drives. Do not place a major heat source directly in the cold-air discharge path if its hot exhaust will then flow across sensitive electronics.
Separate high-loss equipment into another enclosure or thermal zone when density makes reliable airflow impossible. Route cables so they do not block fan intakes, cooling-unit outlets, or vertical convection paths. After assembly, use multiple temperature sensors or thermal imaging under load to confirm that the physical cabinet matches the assumed airflow model.
Undersizing is the more obvious error. When cooling capacity is lower than the actual heat gain at the design condition, cabinet temperature rises until equipment derates, alarms, or fails. Even if the system survives normal operation, it may have no reserve for a dirty filter, a higher summer ambient temperature, or a later controls upgrade.
Oversizing needs to be assessed against the unit’s control method. A fixed-speed compressor may cycle frequently when the load is small relative to capacity; an adjustable-capacity unit should be checked against its minimum controllable output and operating logic. Frequent stopping alone does not prove oversizing: compare the controller demand, actual temperature, hysteresis, door-switch state and alarm history. Do not assume a larger nameplate capacity always consumes more energy; compare model data at the relevant duty.
Capacity should be selected at the actual design point with a justified engineering margin. Include credible worst-case ambient temperature, maximum simultaneous equipment load, surface heat transfer, enclosure arrangement, and expected fouling between maintenance intervals. Avoid adding arbitrary safety factors to already conservative inputs; stacked margins often lead directly to oversizing.
Also consider future modifications explicitly. If spare capacity is needed for a planned drive or PC, document the anticipated additional watts. "Future expansion" without a defined load is not a sizing criterion.
Cooling performance degrades between the day of commissioning and the next service intervention. A design that works only with a perfectly clean filter has no practical operating margin.
Filter inspection frequency should reflect contaminant loading, not a generic calendar interval. Differential pressure, airflow, or temperature trends can provide better evidence than visual inspection alone. Replacement filters must have the correct type and airflow characteristics; substituting denser media may protect against finer dust while restricting flow beyond the fan's available static pressure.
Condenser coils and external heat-transfer surfaces need access for cleaning. If a wall-mounted cooling unit is installed against a structure or in a narrow aisle, routine service may become difficult enough that it is postponed. Fans, seals, condensate drains, and alarms also require inspection. A fan can rotate while delivering inadequate flow because of contamination, damage, or an obstructed path.
For a ventilated cabinet, a rising cabinet-to-ambient temperature difference at comparable heat load can indicate reduced heat removal. For an actively controlled cooling unit, the controller may hold the internal temperature while cooling demand or running time increases. Compare trends at similar load, ambient temperature and setpoint; do not apply one temperature-difference rule to both systems. If cleaning restores the previous performance under comparable conditions, that supports a contamination-related diagnosis rather than proving the original capacity was too small.
A thermal review is needed when a cabinet modification changes either component losses or the air path. An added power supply may contribute little heat yet obstruct the inlet of the device above it. Check both effects before deciding that spare cooling capacity covers the change.
Compare temperatures before and after the change under comparable load, using the same sensor locations. Keep the revised layout, calculation inputs and setpoints together so the next review does not start from an obsolete cabinet drawing.
Use this checklist during design review and commissioning:
- Calculate the actual heat load. Sum component power losses at realistic duty, include all secondary devices, and account for heat transfer through enclosure surfaces.
- Evaluate the installation environment. Document ambient temperature range, dust, oil mist, humidity, washdown exposure, solar load, altitude where relevant, and indoor or outdoor certification requirements.
- Select suitable cooling technology. Confirm that the method can achieve the target internal temperature while maintaining the required enclosure protection.
- Verify capacity at the design point. Use performance data for the expected ambient and internal temperatures, then apply a documented margin for credible variation and fouling.
- Verify airflow design. Maintain device clearances, separate major heat sources, keep supply and return paths open, and check for hot-air recirculation.
- Validate under representative load. Test with doors closed and the machine operating through its demanding production states; log temperatures at multiple internal locations.
- Monitor cabinet temperature. Set actionable warning and alarm thresholds, trend temperature together with operating state and cooling demand where available, and route critical alarms to the appropriate control or maintenance system.
- Plan maintenance requirements. Provide service access and define inspection or cleaning intervals based on the real environment.
- Reassess after modifications. Repeat the heat-load and airflow review when equipment, duty cycle, location, or enclosure configuration changes.
Do not use nominal cooling capacity as the first explanation for every overtemperature alarm. Check the alarm definition, the affected device’s inlet temperature and the operating state first. Then compare the selected cooler’s capacity data with the actual conditions. Use the findings to decide whether to change the layout, service the existing unit or review its size.
For a remote selection review, send the cooling-unit article number, cabinet layout, component-loss estimate, alarm code and definition, and temperature readings with their measurement locations and operating state. Include photographs of the internal air path and the cooling unit’s external intake and discharge clearances. Mark unavailable inputs as unknown. SUWI uses this information for product selection and configuration review; drive and refrigeration faults may also require the equipment manufacturer or an on-site service provider. Review SUWI’s support scope or submit your cooling configuration and measurements for review.
If a replacement is being considered, compare the proposed model with the existing unit at the same operating conditions. For Blue e+ cooling units, check the selected model’s capacity, control range and installation requirements. Variable-speed control does not remove an airflow obstruction or correct an underestimated heat load. Manufacturer guidance is available in Rittal’s enclosure climate-control white paper.