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IMPORTANT - Charge unit in standard cooling mode.
1- Make sure outdoor coil is clean. Attach gauge
manifolds and operate unit at full CFM in cooling mode
with economizer disabled until system stabilizes
(approximately five minutes). Make sure all outdoor air
dampers are closed.
2- Check each system separately with all stages
operating. Compare the normal operating pressures
(see tables 3 - 5) to the pressures obtained from the
gauges. Check unit components if there are
significant differences.
3- Measure the outdoor ambient temperature and the
suction pressure. Refer to the appropriate circuit
charging curve to determine a target liquid
temperature.
Note - Pressures are listed for sea level applications.
4- Use the same thermometer to accurately measure the
liquid temperature (in the outdoor section).
If measured liquid temperature is higher than
the target liquid temperature, add refrigerant to
the system.
If measured liquid temperature is lower than
the target liquid temperature, recover some
refrigerant from the system.
5- Add or remove charge in increments. Allow the
system to stabilize each time refrigerant is added or
removed.
6- Continue the process until measured liquid
temperature agrees with the target liquid
temperature. Do not go below the target liquid
temperature when adjusting charge. Note that
suction pressure can change as charge is adjusted.
7- Example ZH 092S Circuit 1: At 95°F outdoor ambient
and a measured suction pressure of 130psig, the
target liquid temperature is 103°F. For a measured
liquid temperature of 106°F, add charge in
increments until measured liquid temperature agrees
with the target liquid temperature.
C-Compressor Controls
1- High Pressure Switches (S4, S7)
Compressor circuits are protected by a high pressure
switch which cuts out at 640 psig + 10 psig (4413 kPa
+ 70 kPa).
2- High Temperature Limit Switches (S5, S8)
Switches de-energize compressors when the
temperature on top of the compressor exceeds
248
F (120
C). Switches reset when temperature
cools to 169
F (76
C).
3- Defrost Switches (S6, S9)
Defrost switches close to initiate defrost when liquid
line temperature falls to 35
F (1.7
C). The defrost
switch is located on the liquid line between the
outdoor expansion valve and the distributor
4- Defrost Termination Switch (S104)
Defrost pressure switch opens to terminate defrost
when vapor (discharge pressure during cooling and
defrost) pressure reaches 450 psig (3103 kPa).
5- Defrost Controls (CMC1)
Defrost is liquid line temperature initiated and
operates for 14 minutes unless terminated by vapor
line pressure drop.
When the liquid line temperature drops below 35°F,
the defrost switch closes and signals the
defrost
control
that a defrost cycle is needed. If the defrost
switch is still closed after 60 minutes (default), a
defrost cycle begins and operates for 14 minutes.
The defrost pressure switch can terminate the defrost
cycle before the 14 minutes elapses if vapor pressure
reaches 450 + 10 psi
.
Electric heat is energized during defrost to maintain
discharge air temperature.
