CSLB C-20 HVAC ContractorVentilation and Air DistributionHard
A technician measures a system's TESP at 0.95 in. w.c., but the air handler's rated maximum ESP is 0.50 in. w.c. Airflow is noticeably reduced. Which troubleshooting step should be performed FIRST?
- AReplace the blower motor with a higher horsepower unit
- BIncrease the duct static pressure setpoint on the thermostat
- CCheck and replace the air filter if dirty or clogged
- DAdd supplemental return air ducts to the system
Show answer & explanationAnswer & explanation
Correct answer: C. Check and replace the air filter if dirty or clogged
A dirty or clogged filter is the most common cause of excessive static pressure and reduced airflow. It should always be checked first before assuming duct sizing or equipment problems, since it's inexpensive and quick to correct.
Why the other options are wrong
- A. Upsizing the motor addresses symptoms, not the root restriction, and risks further duct/equipment damage.
- B. Thermostats do not control static pressure setpoints.
- D. Adding ducts is a major remodel step, not a first diagnostic action.
Excessive Static Pressure Troubleshooting
When TESP significantly exceeds a blower's rated ESP, first check for the most common cause: a dirty or undersized air filter restricting airflow.
- Dirty filters are the #1 cause of high static pressure
- High static pressure reduces airflow and can overheat equipment
- Always troubleshoot cheapest, most common causes first
Memory trick: Filter first before you tear the ductwork apart.