12-82 Desiccant Replacement
NOTE
Replace desiccant when condenser or refrigerant system is
exposed to air. To eliminate moisture, replace desiccant, then
immediately vacuum system for charging per § 12-81.
1. Remove engine cowling per § 53-21.
2. Recover refrigerant per § 12-81, if not previously accomplished. Remove condenser
cap and replace desiccant.
3. Install cap, special torque cap per § 20-33, and torque stripe.
4. Charge system with refrigerant per § 12-81.
12-83 Leak Detection
Leaks may be detected using several techniques, depending on equipment available. Leak
detection should not be attempted with the aircraft/system running. In addition to safety
hazards, leaks are more difficult to detect with the varying pressures and temperatures
of an operating system.
An empty system should hold full vacuum (27 to 29 inches mercury vacuum at sea level)
with no assistance from the vacuum pump for 20 minutes minimum. If a vacuumed
system creeps up in pressure, a leak may be present. The technician should be thoroughly
familiar with vacuum equipment to ensure leak is in aircraft system and not in vacuum
equipment or connections.
Leaks in a charged system may be detected using a mild soap and water solution applied
to lines and fittings in suspected leak areas (bubbles indicate leaks) or using commercially
available electronic refrigerant detectors. Follow detector manufacturer’s instructions.
Large leaks may be detected audibly if area is quiet or by formation of frost in area of leak.
NOTE
Frost does not necessarily indicate a leak. Normal system
operation and/or charging procedures can cause frost to
accumulate on some components.
NOTE
System pressure is not a reliable indicator of charge state or
the presence of leaks. Because R134a is a liquid/vapor mixture
with the system at rest, pressure will remain constant as more
liquid vaporizes until majority of charge is lost.
JUL 2020 Chapter 12 Servicing Page 12.19
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