21-24 Troubleshooting
1. If air exiting overhead duct is not cold:
POSSIBLE CAUSE TROUBLESHOOT/CORRECTIVE ACTION
Low Refrigerant
Charge/ Refrigerant
Leak
Recover refrigerant per § 12-82. System should operate normally on
approximately 2.5 lb refrigerant.
If less than 2.5 refrigerant is recovered, perform leak detection per § 12-83,
repair leaks if any, and charge system with refrigerant per § 12-82.
Switch or Wiring
Problem Interrupting
Compressor Power
With aircraft not running, temporarily connect a jumper from ground to wire
1898 at main gearbox oil pressure switch. Raise collective to full-up position.
Turn on Master switch and A/C switch on overhead duct (low or high setting
ok). Have observer listen to and observe compressor clutch through cowl door.
Clutch should engage (click and snap against pulley) whenever A/C is switched
on. Remove temporary jumper.
Check wiring at freeze switch (refer to § 21-23), high and low pressure
switches (near compressor assembly), and full-down collective switch. Repair
any damaged wiring or connectors. Check continuity through each switch. All
switches should be closed with a properly charged system and aircraft at rest
on ground. Replace any defective switch.
Failed Compressor
V-Belt
Inspect belt.
Replace belt per § 21-21 as required.
Insufficient
Condenser Airflow
Inspect condenser installation. Verify no blockage and all seals in place.
Remove blockage and/or repair seals to ensure airflow through core.
Extreme
Environmental
Conditions
Extreme temperature and humidity may result in cooling effect less than a
typical automobile.
No corrective action available.
2. If excessive condensation is found near evaporator assembly:
POSSIBLE CAUSE TROUBLESHOOT/CORRECTIVE ACTION
Blocked or Kinked
Evaporator Drain
Verify system is draining normally. After several minutes ground run in humid
conditions with A/C on, water should be seen draining from the drain tube.
If water drainage is not observed, inspect drain line (refer to § 5-45). Correct
any damaged or kinked lines. Clean sediment trap as required. Verify proper
function of check ball.
Extreme Humidity Some condensation is unavoidable in extreme humidity.
Ensure all fresh air vents closed. Limit opening and closing cabin doors as
much as practical to limit humidity entering cabin.
JUL 2020 Chapter 21 Environment Control Page 21.9
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