Pump-Down Control; Unloader Differential Setting - Carlyle 06D Series Application Manual

SUCTION CUT-OFF UNLOADING OPERATION LIMITS
For All 4-Cylinder 06D/E Compressors
L.T. — 502, R-404a and 507 Applications
Operated at Half Load
140
(60)
130
(54)
120
(49)
110
(43)
100
(38)
90
(32)
-40 -30 -20
(-40) (-34) (-29)
SAT. SUCTION TEMP. °F (°C)
Figure 10 – Suction Cut-Off Operation Limits
For 4-Cylinder 06D and 06E Compressors
with R-502, R-404A, R-507
SUCTION CUT-OFF UNLOADING OPERATION LIMITS
For: All 6-Cylinder 06D and 06E Compressors
R-22 High and Medium Temperature Applications
Operated at 1/3 Load (2 Banks Unloaded)
145
(63)
140
(60)
130
(54)
120
(49)
110
(43)
100
(38)
90
(32)
80
(27)
0 10 20
(-18) (-12) (-7)
SAT. SUCTION TEMP. F ( C)
Allow 1/3 load at 0 SST/115 SCT.
Figure 11 – Suction Cut-Off Operation Limits
For 6-Cylinder 06D and 06E Compressors
with R-22
SAFE OPERATIONAL ZONE
-10 0 10 20 30
(-23) (-18) (-12) (-7) (-1)
SAFE
OPERATIONAL
ZONE
30 40 50
(-1) (4) (10)

3.4 Pump-Down Control

Compressors with suction cut-off unloading have inher-
ently greater internal leak paths than compressors with-
out this capacity control feature installed on them.
Compressors with the electric capacity control have been
successfully applied with continuous or automatic pump-
down control. To avoid compressor short-cycling, the
system designer should avoid continuous pump-down
control when the suction pressure cut-in and cut-out
points are within 30 psi (2.1 bar) of each other. Because
the pressure actuated unloaders have a small built-in
high to low pressure path, short-cycling will occur if
continuous or automatic pump-down control is applied.
Do not use continuous or automatic pump-down
control on any compressor equipped with pres-
sure actuated capacity control. Use single pump-out
or solenoid drop (minimum protection) control.

3.5 Unloader Differential Setting

The unloader differential setting is the suction pressure
difference at which the controller loads and unloads the
particular cylinder bank. A differential setting that is too
low could cause the unloader mechanism to short cycle.
For example, when an 06D or 06E compressor unloads,
the suction pressure rises because the compressor
capacity has decreased by one-third or one-half. If the
differential setting is too close, this rise in suction pres-
sure may be enough to load the compressor back-up.
For this reason, Carlyle recommends a minimum differ-
ential setting of 6 to 10 psi (.4 to .7 bar). The final set-
ting should be evaluated for the final application because
many variables are involved:
• Single or multiple compressor application
• Low or medium temperature application
• Unloading 4 or 6 cylinder (1/2 vs. 1/3 load
reduction)
• Refrigerant 12, 22, 502, 507, 404A, or 134a
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