Low Ambient Bypass Valve - Friedrich Hazardgard SH15M30 Series Service Manual

THERMOSTAT
A cross ambient thermostat is used to maintain the
desired comfort level. The thermostat reacts only to a
change in temperature at the bulb location. Important to
the successful operation of the unit is the position of the
sensing bulb in relation to the evaporator.
SENSING
BULB LOCATION
(Part No. 618-225-02)
60° F ( ± 2° ) to 90° F( ± 4° )
ELECTRIC SHOCK HAZARD
Disconnect power to the unit before
servicing. Failure to follow this warning
could result in serious injury or death.
TESTING THE THERMOSTAT
Remove the wires from the thermostat. Turn the
thermostat to its coldest position. Check to see if there is
continuity between the two terminals. Turn the thermostat
to its warmest position. Check continuity to see if the
thermostat contacts open.
Note: The temperature must be within the range listed to
check the thermostat. Refer to the troubleshooting section
in this manual for additional information on thermostat
testing.
12
RANGE: Thermostat
WARNING

LOW AMBIENT BYPASS VALVE

WARNING
HIGH PRESSURE HAZARD
Sealed Refrigeration
refrigerant and oil under high pressure.
Proper safety procedures must be followed,
and proper protective clothing must be
worn when working with refrigerants.
Failure to follow these procedures could
result in serious injury or death.
The Hazardgard unit is designed to operate at low outside
ambient temperatures. This is accomplished by the use
of a bypass valve installed in the refrigeration circuit.
The valve is connected between the discharge line at
the compressor and the suction process tube. The valve
responds to suction pressure which, when reduced in the
system, causes the valve to open and bypass hot gas
from the high pressure side to the low pressure side of
the system. The hot gas entering the compressor mixes
with the cool gas returned through the suction line, thus
increasing the suction pressure. The valve is preset to
open when the suction pressure reaches 88 psig. This
pressure setting cannot be altered. The system can be
operated at outdoor temperatures as low as 45°F before
the evaporator coil will begin to accumulate frost.
To determine if the valve operates, block the return air to
the evaporator coil. Turn on the unit and touch the tube
at the bypass valve outlet which connects to the suction
process tube. When the low side pressure reaches
approximately 88 psig, the valve will begin to open and
the tube will get hot. This method will determine if the
valve is responding to the suction pressure change.
LOW AMBIENT
BYPASS VALVE
System contains