User Guide

Application guidelines
32 AB237986441643en-US0701
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 xed on
the pipe.
DGT protection is required if the high and low
pressure switch settings do not protect the
compressor against operations beyond its
specic 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 evaporating temperature above map border
introduce reliability risks for compressors, such as
high oil dilution rate in oil sump, leading to low
oil viscosity and thus bearing wear. Long time
running in this map region may cause ultimately
compressor failure. Hence Danfoss recommend
customer to use expansion devices (EXV or TXV)
with MOP function. The MOP setting value should
be never higher than the maximum evaporating
pressure specied in the operating envelop.
High and low pressure
protection
Maximum Operating
Pressure (MOP) 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
Condensing temperature (°F)
Evaporating temperature (°F)
Example 2
DGT - limit
Example 1
R22
HP2
LP2LP1
HP1
Discharge line
Insulation
Bracket
Thermostat
Operating conditions