Carrier VECTOR 1800 MT, Operation & Service Manual

Page: 105 / 315

62-11039 4-18
4.7.3 Suction Pressure Operation
At ambient temperatures of 90
_
F (32.2
_
C) or below
When the system is operating in high speed and the
suction pressure is greater than 63 PSIG (4.29 Bars),
both unloaders are unloaded. As the suction pressure
drops below 63 PSIG (4.29 Bars), the UL2 unloader is
loaded. If the suction pressure drops below 32 PSIG
(2.18 Bars), the UL1 unloader is loaded.
When the system is operating in
low speed and the
suction pressure is greater than 65 PSIG (4.42 Bars),
both unloaders are unloaded. As the suction pressure
drops below 64 PSIG (4.35 Bars), the UL2 unloader is
loaded. If the suction pressure drops below 35 PSIG
(2.38 Bars), the UL1 unloader is loaded.
At ambient temperatures of 90
_
F (32.2
_
C) or higher
At ambient temperatures of 90
_
F (32.2
_
C) or higher the
unloading suction pressure settings relative to ambient
temperatures follow a descending straight line. (Refer to
following chart)
15
20
25
30
35
40
45
50
55
60
65
70
80.00 90.00 100.00 110.00 120.00 130.00
HIGH
SPEED
(UL1)
LOW SPEED (UL1)
HIGH
SPEED
(UL2)
LOW SPEED (UL2)
AMBIENT TEMPERATURE
SUCTION
PRESSURE
(Bars/PSIG)
UL1 = FRONT UNLOADER
UL2 = REAR UNLOADER
ABOVE THE LINE = UNLOADED
BELOW THE LINE = LOADED
4.76/
26.7 32.2 37.8 43.3 48.9 54.4
°
C
80 90 100 110 120 130
°
F
4.42/
4.08/
3.74/
3.40/
3.06/
2.72/
1.02/
2.38/
2.04/
1.70/
1.36/
Figure 4--7.Refrigeration System Suction Pressures Unloading (Heat and Defrost Only)