No Cool / Failed Dual Capacitor (Compressor Side)

Quick Summary

Arrived for a no cool call. Indoor unit was running, and the outdoor unit fan was operating, but the system was not cooling. Outdoor condenser coil was heavily dirty, and compressor operation could not be heard initially.

Amp draw check showed the unit was only pulling about 0.4 amps, indicating the condenser fan was running but the compressor was not. Opened the condenser electrical compartment and tested the dual capacitor. Found the compressor side of the 35/5 capacitor had failed.

Replaced the failed 35/5 dual capacitor, verified the new capacitor before startup, and restored power. After replacement, compressor operation returned and system pressures were checked at approximately 138 / 398 psig. Condenser coil was rinsed and the return grille filter was also cleaned.

System Info

System: Split A/C System
Location: Outdoor Condensing Unit / Indoor Return Grille
Outdoor Temp: Not Recorded
Delta T: Not Recorded
Subcooling: Not Recorded
Superheat: Not Recorded

Customer Complaint

Customer stated the system was blowing air but not cooling.

What I Found

Thermostat was calling for cooling.
Indoor unit fan was running on arrival.
Outdoor unit fan was also running, but the system was not producing cool air.
Outdoor condenser coil was heavily dirty.
Compressor could not be clearly heard running.
Checked overall amp draw and found the unit was only pulling about 0.4 amps.
- This indicated the condenser fan was operating, but the compressor was not running.
Opened condenser electrical compartment for testing.
Disconnected power and checked capacitor.
Unit was using a 35/5 dual capacitor.
Tested capacitor and found the compressor side was reading 0 MFD.
Fan side appeared operational.
Replaced failed 35/5 dual capacitor.
Verified new capacitor value before startup:
Common to fan checked good
Common to herm checked good
New capacitor tested acceptable before energizing
Restored power and restarted system.
After capacitor replacement, compressor operation could be heard.
Checked operating pressures and recorded approximately 138 / 398 psig.
Condenser coil was rinsed / cleaned.
Return grille filter was heavily dirty and loaded with dust.
Filter was removed, cleaned outside, and reinstalled.
- Compressor amp draw increased after repair, confirming compressor operation had returned.

Diagnosis

The outdoor fan was still running, which could make the unit appear partially normal at a glance, but the low total amp draw and lack of compressor sound showed the compressor was not operating. Capacitor testing confirmed the compressor side of the 35/5 dual capacitor was failed at 0 MFD.

System was not cooling because the compressor side of the dual capacitor had failed.

After replacing the dual capacitor, the compressor came back on, amp draw increased appropriately, and the system resumed normal operation.

Heavily dirty condenser coil and dirty return filter were also noted. These were not the main electrical failure, but both were contributing maintenance issues and should be documented.

Recommended Action

Replace failed 35/5 dual capacitor
Completed

Verify new capacitor before startup
Completed

Restore power and confirm compressor operation
Completed

Check refrigerant pressures
Completed

Rinse / clean condenser coil
Completed

Clean return grille filter
Completed

Recommend continued monitoring of system performance due to dirty coil / airflow condition
Recommended

Recommend regular filter maintenance
Recommended

Study Note

A system can look like the outdoor unit is running when only the condenser fan is on. If the compressor is not running, checking total amp draw is a fast way to confirm it. In this case, about 0.4 amps pointed to fan-only operation.

On a 35/5 dual capacitor, the 35 MFD side typically serves the compressor and the 5 MFD side serves the condenser fan motor. If the compressor side fails, the fan may still run while the system produces no cooling.

A heavily dirty condenser coil and dirty return filter may not be the direct cause of the no-cool call, but they still affect efficiency and should be cleaned and documented during service.