Metering Device; Reversing Valve Description/Operation - Friedrich PDE07K Service Manual

METERING DEVICE

Capillary Tube Systems
All units are equipped with capillary tube me ter ing de-
vic es.
Checking for re strict ed cap il lary tubes.
1. Connect pressure gauges to unit.
2. Start the unit in the cooling mode. If af ter a few min utes
of op er a tion the pres sures are normal, the check valve
and the cooling cap il lary are not restricted.

REVERSING VALVE DESCRIPTION/OPERATION

The Re vers ing Valve con trols the di rec tion of re frig er ant
flow to the in door and out door coils. It con sists of a
pressure-operated, main valve and a pi lot valve ac tu at ed
by a so le noid plung er. The so le noid is en er gized dur ing the
heating cycle only. The reversing valves used in the PTAC
system is a 2-position, 4-way valve
The single tube on one side of the main valve body is the
high-pressure inlet to the valve from the com pres sor. The
center tube on the opposite side is con nect ed to the low
pressure (suc tion) side of the sys tem. The other two are
connected to the indoor and outdoor coils. Small capillary
tubes connect each end of the main valve cyl in der to the
"A" and "B" ports of the pilot valve. A third cap il lary is a
com mon return line from these ports to the suction tube
on the main valve body. Four-way reversing valves also
have a cap il lary tube from the com pres sor dis charge tube
to the pilot valve.
DANGER OF BODILY INJURY OR DEATH
FROM ELECTRICAL SHOCK
The reversing valve solenoid is connected to
high voltage. Turn off electrical power before
dis con nect ing or connecting high voltage wir ing or
ser vic ing valve.
3. Switch the unit to the heating mode and observe the
gauge readings af ter a few min utes running time. If
the system pressure is low er than nor mal, the heating
cap il lary is re strict ed.
4. If the operating pressures are low er than normal in both
the heating and cool ing mode, the cooling cap il lary is
re strict ed.
The piston assembly in the main valve can only be shifted
by the pressure differential be tween the high and low sides
of the sys tem. The pilot section of the valve opens and
closes ports for the small cap il lary tubes to the main valve
to cause it to shift.
NOTE: System operating pressures must be near
normal before valve can shift.
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