RJ150-30 / Operations and Maintenance Manual
Mobile Aircraft Air Conditioner
Trailer Mounted, Cool Mode Only
______________________________________________________________________________
JANUARY 20, 2004
SECTION 1 - 1
PAGE 19
(3) Filter-Drier:
The refrigerant flows through the filter-drier where moisture and other
impurities are removed. Contaminants in the refrigerant can cause
corrosion of the refrigerant piping, damage to the compressor, and lead to
failure of the refrigerant circuit. (See Figure 9)
(4) Sight Glass:
A sight glass is installed in the refrigerant liquid line near the filter-drier.
(See Figure 9) A less-than-full refrigerant charge will be indicated by
bubbles or foaming action observed when the refrigeration system is in
operation. A color change in the outer ring of the sight glass will indicate
the presence of moisture in the system. (Refer to Section 2-1, Servicing)
(5) Thermostatic Expansion Valve:
The thermostatic expansion valve acts as a pressure-reducing valve and
is used to meter the high-pressure liquid refrigerant into the low-pressure
evaporator coil. Refrigerant flow through this valve is automatically
controlled by refrigerant pressure in the evaporator and by the
temperature of the refrigerant leaving the evaporator. The expansion valve
is located adjacent to the evaporator coil. (See Figure 9.)
(6) Evaporator Coil:
The refrigerant liquid in the low-pressure refrigerant circuit enters the
evaporator coil where it boils by absorbing the latent heat of vaporization
at the low pressure and evaporates into a low-pressure, low-temperature
gas. Heat from the surrounding air flowing through the evaporator coil is
extracted through the finned tubing of the coils by the refrigerant. The
heated gas then returns to the compressor. The chilled air is ducted to the
aircraft. (See Figure 9)
Water condensation is a normal by-product as warm, moist ambient air is
chilled. Gravity-fed condensation collection trays and drain tubing are
mounted below the evaporator coil assembly. Condensate wastewater
drains to ground. (See Figure 9.)
(7) Hot Gas By-Pass Circuit:
A hot gas by-pass valve regulates the refrigerant flow from the
compressor discharge line directly to the evaporator to ensure a constant
running compressor when the unit is in a reduced capacity cooling mode.
This pressure regulating circuit prevents refrigerant pressure from
dropping to a level low enough to cause the compressor to shutdown or
the evaporator coil from freezing. (See Figure 9)
(a) When using R22 or R407c refrigerant, if the suction pressure falls
below 56 - 57 psi (386 - 393 kPa), the hot gas by-pass valve opens to
