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airflow Issue

Makeup Air Unit Problems

Your makeup air unit provides heated, filtered supply—diagnose issues.

Emergency: (877) 489-3727Start Diagnosis

What You're Experiencing

The makeup air unit (MAU) is not functioning correctly. This may manifest as no supply air, insufficient airflow, inadequate heating, or burner issues.

Visual Signs:

  • Supply air not coming from ceiling plenum
  • Booth running too negative (doors hard to open)
  • Booth temperature not reaching setpoint
  • Burner not igniting or cycling

Sound Signs:

  • No sound from MAU blower
  • Unusual sounds from burner (rumbling, popping)
  • Belt squeaking from supply fan

Safety Risks — Read Before Proceeding

medium

No supply air creates excessive negative pressure

Action: Reduce exhaust or stop painting if booth is severely negative.

medium

No heat in cold weather creates coating defects

Action: Do not paint below minimum temperature for your coating system.

Immediate Steps to Take

  1. 1

    Check if MAU is receiving power and run command

  2. 2

    Verify supply fan belt is intact

  3. 3

    Check MAU pre-filters for loading

  4. 4

    Check burner status lights or fault codes

  5. 5

    Verify gas supply valve is open

  6. 6

    Check thermostat/controller setpoint

Common Causes

Here are the most likely reasons you're experiencing this problem, ranked by how often we see them.

Burner Not Igniting

common

The gas burner in the MAU is not lighting. Could be ignition system, gas valve, or flame sensor issue.

Supply Belt Failure

common

The belt driving the supply fan has broken or slipped, preventing proper airflow.

Intake Filters Loaded

common

Pre-filters on the makeup air unit are clogged, restricting the air intake.

Control System Fault

occasional

The MAU controller has faulted or lost its temperature/pressure setpoints.

Damper Actuator Failure

occasional

The modulating damper on the MAU is stuck or the actuator has failed.

Gas Supply Issue

occasional

Gas supply pressure is low or gas valve is not opening due to interlock or fault.

Interactive Diagnostic Tool

Makeup Air Unit Diagnostic

Step 1 of 5

Is the MAU blower running (can you hear/feel air)?

If unsafe at any point: If you smell gas from the MAU or see visible damage, shut off gas supply and call WERCS immediately.

When to Call WERCS

While some issues can be resolved with basic troubleshooting, these situations require professional service:

  • Burner won't ignite or stay lit
  • Supply fan not running
  • Cannot achieve required booth temperature
  • Control system showing fault codes
  • You smell gas or see damage
  • Need annual MAU service or inspection

Priority Service Available

(877) 489-3727

Expert technicians nationwide

Makeup Air Unit Problems FAQ

Common questions about this issue

A makeup air unit (MAU) provides the supply air for your paint booth. It brings in outside air, filters it, heats it (in cold weather), and delivers it to the booth ceiling plenum. This replaces the air being exhausted and maintains proper booth pressure and temperature.
MAUs should have professional service at least annually, including burner inspection, filter changes, belt check, and control system verification. High-use facilities may need quarterly maintenance.
Not recommended. Running exhaust without supply air creates severe negative pressure, stresses booth structure, pulls in unfiltered shop air (contamination), and in cold weather doesn't heat the booth. Always verify MAU operation before painting.

Have a question not answered here?

Call us at (877) 489-3727

Related Problems

Burner Not IgnitingNot HeatingPressure Imbalance

Related Parts & Components

Makeup Air UnitIgnition ModuleGas Valve

Can't Fix It? We Can.

WERCS expert technicians service paint booths and extraction systems nationwide. 24/7 emergency service available.

Call (877) 489-3727Request Service Quote