Temperature Creep in Indoor Control Cabinets (Part 2) How to Diagnose “Slow Overheating” and Prevent Nuisance Trips with Early Warnings

Last time, I shared a practical sizing guide for industrial indoor cabinet AC (300–3000W) in power plants, automotive lines, and robot cells. This follow-up focuses on what happens 6–10 weeks after commissioning — when cabinets start alarming even though “nothing seems broken.”

Many indoor cabinet overheating events are not sudden failures. They’re temperature creep: a slow drift where the system holds setpoint at first, then gradually loses effective cooling until nuisance trips and downtime appear.

1) Why “Indoor” Cabinets Still Drift into Overheat

People often assume indoor = stable ambient. In real production environments, cabinet intake air can be much hotter than the room average.

Typical drivers:

• Heat pockets near welding cells, compressors, furnaces, crowded MCC rooms
• Heat load creep after upgrades (extra drives, PSUs, IPCs, networking)
• Airflow short-circuit inside the cabinet (cold air doesn’t reach the hot spot)
• Dust / oil mist loading filters and fouling heat exchangers
• Maintenance reality (filters aren’t serviced as often as planned)

Key idea: temperature creep is usually a system behavior, not a single component failure.Temperature diagramTemperature diagramTemperature diagram

Temperature diagram

2) The Fastest Way to Confirm Temperature Creep: Look at the Trend, Not the Alarm

An alarm tells you “it’s already hot.” A trend tells you why it’s getting hot.

If you have even basic temperature logging, check:

• Cabinet temperature slope (how fast it rises during peak production)
• ΔT to ambient near cabinet intake (not HVAC setpoint)
• Duty cycle increase (AC running longer to maintain the same setpoint)
• Time-to-threshold (how many days/weeks it took to reach alarms)

A common pattern:

1. Setpoint maintained at first (AC duty cycle increases quietly)
2. Effective capacity drops (filter loading / coil fouling / higher local ambient)
3. Temperature rises faster (hot spot dominates)
4. Nuisance trips / downtime risk

3) Root Cause Triage: What the Trend Usually Means

Here’s a field-friendly “if you see X, suspect Y” guide:

A) Temperature rises slowly over weeks, especially at peak hours

Suspect: filter loading / coil fouling / gradual airflow reduction Action: inspect filters, check condenser/evaporator cleanliness, verify airflow path

B) Sudden step-up after a line upgrade / added equipment

Suspect: heat load creep Action: re-estimate cabinet heat dissipation and confirm cooling margin

C) One cabinet is problematic while nearby cabinets are fine

Suspect: local heat pocket or cabinet placement issue Action: measure peak ambient near cabinet intake; consider airflow around cabinet, nearby heat sources

D) Alarms happen even when average cabinet temp looks acceptable

Suspect: hot spot + internal airflow short-circuit Action: improve internal ducting/baffles so cooled air reaches drives/PSU hot zones

4) The Two-Loop Airflow Concept (Why Sealing Matters Indoors Too)

A proper cabinet AC relies on:

• an internal sealed air loop (return → evaporator → supply) to keep contaminants out
• an ambient air loop to reject heat through the condenser

When sealing is poor (gaskets/cable glands/wiring gaps), the cabinet becomes a “dust pump,” accelerating airflow loss and maintenance cost — even indoors.

temperature diagram

5) Early Warnings That Actually Reduce Maintenance Cost

If you manage many cabinets, don’t wait for over-temp shutdown alarms. Use early warnings that predict creep:

Recommended early-warning signals

• Service reminder / filter interval (based on dust/oil-mist reality, not calendar hope)
• Fan status / airflow-related alarm (fan failure or abnormal behavior)
• Temperature trend alert (slope-based warning before threshold)
• Optional: runtime/duty-cycle trend (same setpoint but longer runtimes = capacity margin shrinking)

This shifts you from “emergency call-outs” to “planned maintenance,” which is where the real cost savings are.

6) Practical Fix Package (What Works in Production Sites)

If you want a minimal, high-impact package:

1. Measure peak ambient at cabinet intake (hottest hour, hottest zone)
2. Confirm heat load creep after upgrades
3. Fix internal airflow path to hot components (no short-circuit)
4. Make maintenance doable (fast filter access + simple SOP)
5. Enable early warnings (service reminder + fan status + trend alerts)

That’s usually enough to stop repeat alarms without over-engineering.