Friedrich YL24J35, Service & Parts Manual

Page: 23 / 62

TTJ-0197 (1/97) (Page 23 of 64)
This valve is temperature sensitive and will open when
the outside temperature reaches 40°F. The valve will
close gradually as the temperature rises above 40°F to
fully close at 60°F.
Figure 16: DRAIN PAN VALVE
REVERSING VALVE
(Heat Pump Model Only)
A reversing valve is used to change the refrigerant flow
within the system to permit heating or cooling (see Fig-
ure 17.)
The reversing valve consists of a main valve body which
houses the slide and piston, plus a pivot valve which is
activated by a solenoid.
There are three tubes connected to one side of the main
valve body and one tube on the opposite side. The single
tube is connected to the compressor discharge line. The
center tube on the opposite side is the common suction
line to the compressor. The outside tubes are connected
to the indoor and outdoor coils.
Figure 17: REVERSING VALVE
The pilot valve is responsible for directing the refriger-
ant flow to the indoor or outdoor coil. There are three
small tubes connected to the pilot valve body. The cen-
ter pilot tube is the common pilot tube and is connected
to the center suction line. The outside tubes are con-
nected to each end of the main valve body. The pilot
valve consists of a needle valve and spring. When the
solenoid is deenergized, the spring tension closes one
pilot port while the others remain open. When the sole-
noid is energized, the opposite end is closed. The pis-
ton in the main valve is pressure operated and will al-
ways travel in the direction of the open pilot tube port
which provides a path to the center tube. Pressure which
will increase in the opposite end of the valve will es-
cape through a bleed port located in each piston. When
deenergized, the valve will be in the cooling position.
TESTING REVERSING VALVE
Occasionally, the reversing valve may stick in the heat-
ing or cooling position or in the mid-position.
When stuck in the mid-position, par t of the discharge
gas from the compressor is directed back to the suc-
tion side, resulting in excessively high suction pressure.
Check the operation of the valve by starting the system
and switching the operation from "cooling" to "heating"
and then back to "cooling". Do not hammer on the valve.
If valve fails to change its position, test the voltage to
the valve coil while the system is in the heating cycle. If
voltage to coil is satisfactory, replace reversing valve.
Should the valve fail to shift from cooling to heating,
block the air flow through the indoor coil and allow dis-
charge pressure to build in the system. Then switch the
system from cooling to heating.
If valve is stuck in the heating position, block the air
flow through the indoor coil and allow discharge pres-
sure to build in the system. Then switch the system
from heating to cooling.
Should the valve fail to shift in either position after in-
creasing the discharge pressure, replace the valve.
NOTE: When brazing a reverse valve into the system,
it is of extreme importance that the tempera-
ture of the valve does not exceed 250°F at any
time.
Wrap the reversing valve with a large rag satu-
rated with water. "Re-wet" the rag and thor-
oughly cool the valve after brazing operation of
the four joints involved.