Friedrich Twintemp, Service Manual

Page: 33 / 68

METErING dEvICE
Capillary Tube Systems
All units are equipped with capillary tube metering
devices.
Checking for restricted capillary tubes.
1. Connect pressure gauges to unit.
2. Start the unit in the cooling mode. If after a few minutes
of operation the pressures are normal, the check valve
and the cooling capillary are not restricted.
3. Switch the unit to the heating mode and observe the
gauge readings after a few minutes running time. If
the system pressure is lower than normal, the heating
capillary is restricted.
4. If the operating pressures are lower than normal in both
the heating and cooling mode, the cooling capillary is
restricted.
Proper safety procedures must be followed,
and proper protective clothing must be worn
when working with a torch.
Failure to follow these procedures could
result in moderate or serious injury.
WARNING
BURN HAZARD
hErMETIC COMPONENTS ChECK
One-way Check Valve
(Heat Pump Models)
ChECK vALvE
A unique two-way check valve is used on the reverse cycle
heat pumps. It is pressure operated and used to direct the
flow of refrigerant through a single filter drier and to the
proper capillary tube during either the heating or cooling
cycle.
NOTE: The slide (check) inside the valve is made of teflon.
Should it become necessary to replace the check valve,
place a wet cloth around the valve to prevent overheating
during the brazing operation.
CHECK VALVE OPERATION
In the cooling mode of operation, high pressure liquid enters
the check valve forcing the slide to close the opposite port
(liquid line) to the indoor coil. Refer to refrigerant flow chart.
This directs the refrigerant through the filter drier and cooling
capillary tube to the indoor coil.
In the heating mode of operation, high pressure refrigerant
enters the check valve from the opposite direction, closing
the port (liquid line) to the outdoor coil. The flow path of the
refrigerant is then through the filter drier and heating capillary
to the outdoor coil.
Failure of the slide in the check valve to seat properly in
either mode of operation will cause flooding of the cooling
coil. This is due to the refrigerant bypassing the heating or
cooling capillary tube and entering the liquid line.
COOLING MODE
In the cooling mode of operation, liquid refrigerant from
condenser (liquid line) enters the cooling check valve
forcing the heating check valve shut. The liquid refrigerant
is directed into the liquid dryer after which the refrigerant
is metered through cooling capillary tubes to evaporator.
(Note: liquid refrigerant will also be directed through the
heating capillary tubes in a continuous loop during the
cooling mode).
HEATING MODE
In the heating mode of operation, liquid refrigerant from
the indoor coil enters the heating check valve forcing the
cooling check valve shut. The liquid refrigerant is directed
into the liquid dryer after which the refrigerant is metered
through the heating capillary tubes to outdoor coils. (Note:
liquid refrigerant will also be directed through the cooling
capillary tubes in a continuous loop during the heating
mode).
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CUT/SEVER HAZARD
WARNING
Be careful with the sharp edges and corners.
Wear protective clothing and gloves, etc.
Failure to do so could result in serious injury.