Air conditioning zoning system repair in Sunnyvale, CA – upper zone running constantly issue fixed
The homeowner contacted us after noticing that the upper level air conditioning zone was running constantly and would not shut off properly. This kind of issue often leads to uneven temperatures, higher energy bills, and unnecessary wear on the HVAC system.
Air Conditioner Issue Diagnosis and Repair – Stuck Zoning Damper Resolved
The homeowner contacted us after noticing that the upper level air conditioning zone was running constantly and would not shut off properly. This kind of issue often leads to uneven temperatures, higher energy bills, and unnecessary wear on the HVAC system.
We performed a full diagnostic inspection (free with repair) and traced the issue to the zoning control system.
What We Found
The system is equipped with motorized dampers that control airflow to different parts of the house. In this case, the damper responsible for the upper level zone had become mechanically stuck.
The internal metal blade inside the duct was jammed, preventing the actuator motor from rotating it correctly. Because the damper remained open, conditioned air continuously flowed to the upstairs area, causing that zone to run all the time.
Additional Challenge
The failed damper assembly was installed at the beginning of the plenum in a very tight and difficult-to-access location. The surrounding duct section had also been heavily sealed with mastic, making removal and replacement more labor-intensive.
Recommended Repair
- ✅ Remove damaged duct section
- ✅ Install new 12” Honeywell ARD12TZ zoning damper
- ✅ Rebuild and reseal duct connection
- ✅ Test actuator movement and zoning operation
- ✅ Verify proper airflow control between zones
Estimate
Part + Labor: Under $1100
Why This Repair Matters
A properly working zoning damper helps maintain comfort in each area of the home while reducing strain on the HVAC system. Once repaired, the upper level zone will respond normally and stop overcooling or running nonstop.
If one area of your home stays on constantly or temperatures feel unbalanced, your zoning system may need professional inspection.
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