Operating conditions
The discharge gas temperature must not exceed
275°F. The discharge gas thermostat accessory kit
(code 7750009) includes all components required
for installation, as shown below. The thermostat
must be attached to the discharge line within
150 mm from the compressor discharge port and
must be thermally insulated and highly fixed on
the pipe.
DGT protection is required if the high and low
pressure switch settings do not protect the
compressor against operations beyond its
specific application envelope. Please refer to the
examples on following page, which illustrates
where DGT protection is required (ex.1) and
where it is not (ex.2).
A discharge temperature protection device must
be installed on all heat pumps. In reversible
air-to-air and air-to-water heat pumps the
discharge temperature must be monitored
during development test by the equipment
manufacturer.
The DGT should be set to open at a discharge gas
temperature of 275°F.
The compressor must not be allowed to cycle
on the discharge gas thermostat. Continuous
operations beyond the compressor’s operating
range will cause serious damage to the
compressor.
Discharge temperature
protection
A high-pressure (HP) safety switch is required to
shut down the compressor should the discharge
pressure exceed the values shown in the table
next page. The high-pressure switch can be set
to lower values depending on the application
and ambient conditions. The HP switch must
either be placed in a lockout circuit or consist of
a manual reset device to prevent cycling around
the high-pressure limit. If a discharge valve is
used, the HP switch must be connected to the
service valve gauge port, which must not be
isolated.
High and low pressure
protection
High pressure
Example 1
(R22, SH = 20°F)
LP switch setting:
LP1 = 26 psig (1.4°F)
HP switch setting:
HP1 = 363 psig (143.6°F)
Risk of operation beyond the application envelope.
DGT protection required.
Example 2
(R22, SH = 20°F)
LP switch setting:
LP2 = 42 psig (19.4°F)
HP switch setting:
HP2 = 305 psig (131°F)
No risk of operation beyond the application envelope.
No DGT protection required.
80
90
100
110
120
130
140
150
160
-10
0
10
20
30
40
50
60
C
ondensing t
emper
atur
e (°F)
Evaporating temperature (°F)
Example 2
DGT - limit
Example 1
R22
HP2
LP2
LP1
HP1
Discharge line
Insulation
Bracket
Thermostat
Application guidelines
30
FRCC.PC.003.A5.22
