Why Are Server Racks Overheating When the Air Conditioning Is Running? Malaysia

A data-centre air-conditioning system may appear to operate normally while individual server racks continue to overheat.

Room temperature alone does not prove that sufficient cooling air is reaching every equipment intake.

The actual problem may involve weak airflow, hot-air recirculation, low raised-floor pressure, blocked ventilation, poor containment or uneven equipment load.

A structured server rack cooling and airflow investigation helps Malaysian data-centre teams identify the cause before lowering the thermostat or adding unnecessary cooling capacity.

Why Can Racks Overheat in a Cool Room?

A central room sensor may show an acceptable temperature while:

• Rack-top inlets receive warm air

• High-density racks receive insufficient airflow

• Hot exhaust returns to equipment intakes

• Floor tiles are incorrectly positioned

• Cable bundles block exhaust air

• Cooling air bypasses the racks

• One cooling unit has weak airflow

• Containment gaps allow air mixing

• Equipment fans are failing

• Cooling distribution is unbalanced

The temperature experienced by the servers matters more than a single reading at the room wall.

Common Warning Signs

Look for:

• Rack temperature alarms

• Hot front-top rack area

• Servers increasing fan speed

• One rack warmer than nearby racks

• Cool room centre but hot equipment inlet

• Large top-to-bottom temperature difference

• Hot air entering the cold aisle

• Uneven floor-tile airflow

• Cooling units operating continuously

• Equipment restarting or reducing performance

• Repeated nighttime temperature rise

Essential Cooling Investigation Tools

A practical toolkit may include:

• Temperature and humidity meter

• Elitech RC-5 Temperature Data Logger

• Elitech GSP-6 Pro Temperature and Humidity Data Logger

• Air velocity meter or anemometer

• Airflow meter

• Differential pressure meter

• Noyafa NF-522 Thermal Camera

• AC/DC clamp meter

• Sound level meter

• Vibration meter

• Suitable temperature probes

No single instrument explains the complete cooling problem.

Step 1: Confirm the Rack Inlet Temperature

Measure temperature at the rack’s:

• Front-bottom

• Front-middle

• Front-top

These positions represent the air entering the equipment when the rack follows a front-to-rear airflow arrangement.

Record:

• Exact position

• Time

• Rack load

• Cooling units operating

• Door condition

• Active alarms

Avoid relying only on room temperature.

Step 2: Measure the Rack Exhaust Temperature

Measure at:

• Rear-bottom

• Rear-middle

• Rear-top

A warm exhaust is expected because the equipment transfers heat to the air.

The concern is whether this warm exhaust returns to the rack front or escapes into the cold aisle.

Step 3: Compare Front and Rear

Temperature measurements should be interpreted with airflow and equipment-load information.

Step 4: Compare Nearby Racks

Check whether the overheating affects:

• One rack

• One row

• One cold aisle

• One cooling zone

• All racks

• High-density racks only

• Racks farthest from the cooling unit

If only one rack is affected, inspect its equipment, blanking panels, cables and fans first.

If an entire zone is affected, investigate cooling distribution and pressure.

Step 5: Measure Rack-Inlet Airflow

Measure airflow at:

• Rack front-bottom

• Rack front-middle

• Rack front-top

• Floor grille or perforated tile

• Nearby normal rack

• Problem rack

Maintain consistent:

• Sensor orientation

• Measurement distance

• Measurement duration

• Rack-door condition

• Cooling operating condition

A single quick reading may not represent fluctuating airflow.

Step 6: Check Floor Tiles and Grilles

Inspect for:

• Blockage

• Dirt

• Stored items

• Incorrect position

• Damaged tile

• Closed damper

• Excessive airflow at another location

• Grille placed in a hot aisle

• Unsealed floor opening

More airflow is not automatically better if it bypasses equipment or disrupts the designed pressure distribution.

Do not move floor tiles without approval from the responsible facility team.

Step 7: Measure Raised-Floor Differential Pressure

Where raised-floor cooling is used, measure pressure between:

• Underfloor plenum

• Server room

Low or uneven pressure may reduce cooling airflow at distant or high-load racks.

Compare several locations using the same method.

Possible causes of low pressure include:

• Open floor penetrations

• Missing floor panels

• Excessive open grilles

• Underfloor obstruction

• Cooling-fan problem

• Air leakage

• Incorrect damper position

Step 8: Inspect Underfloor Conditions

Only authorised personnel should open raised-floor panels.

Check for:

• Cable congestion

• Abandoned cables

• Airflow obstruction

• Open penetrations

• Missing seals

• Water leakage

• Dust accumulation

• Incorrect ducting

• Damaged floor supports

Protect the open floor area against falls.

Step 9: Inspect Blanking Panels

Unused spaces in a rack should be reviewed for appropriate blanking panels.

Missing panels may allow hot exhaust air to circulate from the rear to the front.

Inspect:

• Empty rack units

• Side gaps

• Space around equipment

• Openings above and below equipment

• Damaged panels

Use components suitable for the rack and facility design.

Step 10: Check Cable Management

Rear cable congestion may:

• Block server exhaust

• Restrict equipment fans

• Trap hot air

• Prevent rack doors from closing

• Create difficult maintenance access

• Reduce airflow through network switches

Inspect cable bundles without disconnecting or moving critical connections unnecessarily.

Step 11: Check Equipment Orientation

Confirm that servers, switches and other devices follow the intended airflow direction.

Incorrectly oriented equipment may:

• Discharge hot air toward another device

• Draw air from the hot aisle

• Create a local recirculation path

• Disrupt containment

Network switches may have different airflow directions even when they appear physically similar.

Step 12: Inspect Equipment Fans

Look and listen for:

• Fan alarm

• No rotation

• Reduced speed

• Rattling

• Grinding

• Dust accumulation

• Uneven exhaust airflow

• High equipment temperature

A sound level meter or vibration meter can help document abnormal fan condition.

Step 13: Perform Thermal Inspection

Use a thermal camera to inspect:

• Rack front

• Rack rear

• Top, middle and bottom

• Server air intakes

• Exhaust areas

• Network switches

• Power supplies

• Rack PDUs

• Electrical connections

• Cooling equipment

The Noyafa NF-522 Thermal Camera may help distinguish a general cooling problem from one hot component.

Thermal images show surface-temperature patterns, not direct air temperature.

Step 14: Install Temperature Data Loggers

A spot measurement may miss:

• Nighttime cooling reduction

• Short cycling

• Temporary overload

• Standby-unit changeover

• Door-opening effects

• Gradual temperature rise

Place Elitech RC-5 loggers at:

• Problem rack front-top

• Problem rack front-bottom

• Nearby reference rack

• Cooling-zone reference point

Use the Elitech GSP-6 Pro when relative humidity must also be monitored.

Step 15: Review Cooling-Unit Operation

Check:

• Supply-air temperature

• Return-air temperature

• Fan status

• Filter condition

• Coil condition

• Compressor or chilled-water operation

• Valve position

• Alarm history

• Operating schedule

• Standby-unit status

A cooling unit may be running but delivering insufficient airflow or cooling capacity.

Step 16: Inspect Cooling Filters and Coils

Dirty filters or coils may reduce airflow and cooling performance.

Possible signs include:

• Lower air velocity

• Higher fan effort

• Abnormal differential pressure

• Reduced cooling output

• Longer operating time

• Uneven discharge

Maintenance should follow the cooling-equipment manufacturer’s procedure.

Step 17: Check Hot-Aisle and Cold-Aisle Containment

Inspect for:

• Open doors

• Missing roof panels

• Damaged curtains

• Unsealed cable openings

• Gaps above racks

• Gaps between racks

• Incorrect rack placement

• Incomplete end-of-row separation

Small gaps may allow significant hot and cold air mixing.

Step 18: Check for Cooling-Air Bypass

Cooling air may return to the cooling unit without passing through IT equipment.

Possible bypass paths include:

• Open floor grilles without racks

• Gaps around rack bases

• Unsealed cable penetrations

• Open spaces beside racks

• Incorrect tile locations

• Poor containment

Correcting bypass airflow may improve cooling without increasing total capacity.

Step 19: Review Rack Electrical Load

High-load racks require more cooling.

Review:

• Rack PDU load

• Server utilisation

• Newly installed equipment

• PoE-switch load

• Storage equipment

• Redundant power supplies

• Load distribution by rack

A rack that recently received additional equipment may exceed the available local airflow.

Step 20: Check Electrical Hotspots

Not every hot rack condition is caused by air temperature.

Thermally inspect:

• Rack PDU outlets

• Plugs

• Power adapters

• Cable connections

• Power-supply modules

• Branch connections

Qualified technicians may use a clamp meter to compare current and load.

Step 21: Check Room Pressure and Air Entry

Measure differential pressure where appropriate between:

• Server room and corridor

• Cold aisle and room

• Hot aisle and room

• Raised floor and room

• Server room and adjacent mechanical space

Incorrect pressure may cause:

• Warm-air entry

• Humid-air entry

• Containment leakage

• Uncontrolled airflow

Interpret results according to the designed ventilation strategy.

Step 22: Review Door Activity

Repeated or extended door opening may affect:

• Room pressure

• Temperature

• Humidity

• Airflow pattern

• Containment performance

Compare environmental-logger timestamps with access records where permitted.

Airflow Problem Versus Heat-Load Problem

Both conditions may occur together.

Airflow Meter Versus Differential Pressure Meter

Use both when raised-floor or containment performance is involved.

Thermal Camera Versus Temperature Logger

Example: Rack Top Is Hotter Than Bottom

Possible causes include:

• Weak upper-rack airflow

• Hot-air recirculation

• Missing blanking panels

• High-load equipment at top

• Cable obstruction

• Containment gap

Measure at three heights and inspect the rack thermally.

Example: One Rack Is Hot but Nearby Racks Are Normal

Check:

• Rack load

• Equipment fans

• Blanking panels

• Cable congestion

• Floor-tile airflow

• Equipment orientation

• Local PDU hotspot

Example: Entire Cold Aisle Is Warm

Check:

• Cooling-unit output

• Raised-floor pressure

• Floor grilles

• Containment

• Cooling schedule

• Chilled-water availability

• Total heat load

Example: Temperature Rises Only at Night

Possible causes include:

• Reduced cooling schedule

• Standby-unit change

• Different equipment workload

• Building HVAC change

• Doors opened during cleaning

• Automatic control problem

Use data loggers to capture the timing.

Example: Room Centre Is Cool but Servers Alarm

This often indicates that the central reading does not represent equipment inlet conditions.

Measure directly at:

• Rack front-top

• Rack front-middle

• Rack front-bottom

Also check airflow and hot-air recirculation.

Corrective Actions

Depending on the confirmed cause:

• Install missing blanking panels

• Improve cable management

• Seal containment gaps

• Correct equipment orientation

• Clear blocked ventilation

• Service cooling filters or coils

• Repair failed fans

• Adjust approved floor grilles

• Seal floor penetrations

• Balance airflow

• Redistribute rack load

• Repair electrical hotspots

• Correct cooling controls

• Add permanent monitoring

Changes should follow the approved facility procedure.

Common Cooling Troubleshooting Mistakes

Avoid:

• Relying only on room temperature

• Measuring only at rack centre

• Checking temperature without airflow

• Moving floor tiles without assessment

• Lowering the thermostat before locating the cause

• Ignoring blanking panels

• Ignoring rear cable congestion

• Treating thermal images as air-temperature readings

• Comparing racks with different loads

• Checking only during office hours

• Failing to record cooling-unit status

• Closing the finding without retesting

Recommended Cooling Investigation Kit

A practical toolkit may include:

• Airflow meter

• Differential pressure meter

• Temperature and humidity meter

• Elitech RC-5

• Elitech GSP-6 Pro

• Noyafa NF-522 Thermal Camera

• AC/DC clamp meter

• Sound level meter

• Vibration meter

• Suitable probes and documentation tools

Verify the Correction

After corrective work:

1. Repeat rack inlet temperature measurements.

2. Repeat top, middle and bottom comparisons.

3. Repeat airflow measurements.

4. Recheck differential pressure.

5. Scan the rack thermally.

6. Review rack electrical load.

7. Continue data logging.

8. Compare with the original condition.

9. Confirm that alarms do not return.

10. Document the final result.

Measure Cooling Where the Equipment Uses It

An operating air conditioner does not guarantee effective rack cooling.

The cooling air must reach the correct equipment intakes, pass through the equipment and return without mixing excessively with the cold supply.

Combining rack-inlet temperature measurement, airflow testing, differential-pressure measurement, thermal imaging and data logging helps data-centre teams determine whether overheating is caused by cooling capacity, airflow distribution, heat load or recirculation.

This supports targeted corrective work instead of simply reducing the thermostat setting.

Contact MTM Precision

MTM Precision Sdn. Bhd.

Showroom & Service Centre

No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia

🌐 Website: www.mtmpre.com.my
📧 Email: mtmpre@yahoo.com
📱 WhatsApp: +6016-660 7346