Cooling Tunnel Troubleshooting: Causes & Fixes

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Problems on this page:

Product not set at the exit Condensation on product at the exit Marks or bloom from cooling Belt running to one side Belt slipping or stopping Tunnel not reaching temperature Uneven cooling across the belt Water dripping onto product Build-up inside the tunnel Product sticking to the belt at the exit Fans noisy or vibrating

Product not set at the exit

Hits OEE: Quality

Symptoms: Product leaves the tunnel soft or marks at the next step.

Tunnel temperature too high

Check each zone against the recipe.

Belt speed too fast

Check the belt speed for the product.

Airflow low

Check fans and filters.

Product loaded too densely

Space the product.

Prevention: Product hardness checked at the exit.

Condensation on product at the exit

Hits OEE: Quality

Symptoms: Product sweats when it leaves the tunnel.

Exit zone too cold for the room

Raise the last zone so the product leaves above the room dew point.

Humid packing room

Control the packing room humidity.

Product waiting in a warm area

Pack product soon after the tunnel.

Door or cover open

Keep tunnel covers closed.

Prevention: Room dew point monitored during production.

Marks or bloom from cooling

Hits OEE: Quality

Symptoms: Product shows marks, streaks or bloom after cooling.

First zone too cold

Cool gradually as the recipe sets.

Air blowing straight onto the product

Check the air guides.

Product not tempered

Check the temper before the tunnel.

Belt dirty

Clean the belt.

Prevention: Appearance checked on samples.

Belt running to one side

Hits OEE: Availability

Symptoms: The belt drifts and rubs the frame.

Rollers misaligned

Align the rollers.

Tension uneven

Set the tension evenly.

Build-up on rollers

Clean the rollers.

Belt worn or stretched

Replace the belt.

Prevention: Belt tracking checked at start-up.

Belt slipping or stopping

Hits OEE: Availability

Symptoms: The belt slips on the drive or stops.

Tension too low

Set the belt tension.

Drive roller worn

Replace the lagging.

Sugar or fat build-up on the drive

Clean the drive roller.

Motor or gearbox fault

Check the drive.

Prevention: Drive checked on the maintenance round.

Tunnel not reaching temperature

Hits OEE: Availability

Symptoms: Zone temperatures stay above the set point.

Coils iced up

Defrost and check the defrost cycle.

Refrigeration plant short of capacity

Check the chiller or refrigeration plant.

Fans failed

Replace failed fans.

Covers leaking

Check cover seals.

Prevention: Zone temperatures logged continuously.

Uneven cooling across the belt

Hits OEE: Quality

Symptoms: Product on one side is softer than on the other.

Fan failed on one side

Replace the failed fan.

Air ducts blocked

Clean the ducts.

Product spread unevenly

Spread product across the belt.

Covers not seated

Seat the covers.

Prevention: Product checked at both edges.

Water dripping onto product

Hits OEE: Quality

Symptoms: Drops of water fall on the product or belt.

Drains blocked

Clear the drains.

Defrost water not collected

Check the drip trays.

Condensation on covers

Check insulation and seals.

Cleaning water left in the tunnel

Dry the tunnel after cleaning.

Prevention: Drip trays and drains checked at each clean.

Build-up inside the tunnel

Hits OEE: Quality

Symptoms: Crumbs and coating build up inside and fall on product.

Cleaning interval too long

Shorten the interval.

Access to inside parts difficult

Open covers fully for cleaning.

Scrapers worn

Replace belt scrapers.

No inspection after cleaning

Check with a light after cleaning.

Prevention: Cleaning verified before start-up.

Product sticking to the belt at the exit

Hits OEE: Quality

Symptoms: Product tears, leaves pieces behind or has a rough base when it is lifted off the belt.

Product entering the tunnel too warm or too soft

Check the product temperature at the tunnel infeed and the time it waits after the enrober or depositor.

Belt surface not suited to the product

Ask the belt supplier for a surface with better release for this product.

Belt wet or greasy after cleaning

Make sure the belt is clean and fully dry before product reaches it.

Exit zone not cold enough to set the base

Check the last zone temperature and the air reaching the underside of the belt.

Prevention: Product base checked at the exit at the start of each run.

Fans noisy or vibrating

Hits OEE: Availability

Symptoms: A tunnel fan becomes noisy, vibrates or trips its motor protection.

Ice or product build-up on the blades

Clean the blades, since uneven build-up throws the fan out of balance.

Fan motor bearings worn

Replace the bearings or the motor before it fails during production.

Fan guard or mounting loose

Tighten the guard and mounting bolts.

Blade damaged during cleaning

Inspect the blades after cleaning and replace damaged ones.

Prevention: Fan noise and vibration checked on the maintenance round.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: enrober · depositor · spiral conveyor · chiller · flow wrapper · pasta extruder · tortilla press · chocolate tempering machine

Stop the same fault coming back

Recurring cooling tunnel stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

Book a Fabrico demo

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover