Commercial problem guide
Find out why both functions are operating before switching one off.
Start with the intended function and a common timeline. The useful result is a verified explanation and, where needed, a correction that still satisfies temperature, moisture and ventilation requirements.
Published and reviewed by Gulf Coast Technologies, LLC. Sources, corrections and review method.
Recognize the pattern
- Overlapping heating and cooling commands
- Supply conditions do not match commanded state
- Comfort is maintained but runtime or energy use is unexplained
Systems that may be involved
- Intended dehumidification and reheat
- Different zone demands or approved operating modes
- Sensor, schedule or sequence problems
- Valve leakage or physical response different from command
First useful evidence
- Approved sequence and current overrides
- Aligned mode, command, feedback and temperature trends
- Qualified checks of actual equipment response
- Baseline and acceptance target before changes
Expensive shortcuts to avoid
- Disabling all reheat without checking moisture control
- Treating a command as proof that a valve shut
- Claiming savings from a short trend without a valid baseline
Questions worth separating
Is simultaneous heating and cooling always a fault?
No. The intended function matters. Establish it before deciding that the overlap is unnecessary.
Can a zero command prove a valve is closed?
No. Physical response needs verification with appropriate safe measurements.
Can runtime alone establish savings?
No. Use a suitable measurement-and-verification approach and account for changed conditions.
Source trail
Check the basis for this guide.
New source links and claims reviewed November 4, 2026. A source explains the stated mechanism; it does not diagnose a particular building or endorse ICY.
Guides to Re-Tuning Measures
Economizer suitability depends on conditions and controls; damper command is not outdoor-air fraction; Some reheat serves dehumidification; excessive simultaneous heating and cooling needs sequence-based investigation
Read the primary sourceHVAC Commissioning
Functional verification; equipment and controls; dampers and schedules; ventilation and delivered airflow
Read the primary sourceMeasurement and Verification Options for Federal Energy- and Water-Saving Projects
Baselines; retrofit isolation; whole-building verification; calibrated simulation
Read the primary sourceThese observations are starting points. Applicable local requirements, manufacturer instructions and the responsible qualified provider control hazardous or regulated work.