CAUTION: Do not attempt to start the compressor without at
least 8 hours of crankcase heat or compressor
damage will occur.
To continue charging refrigerant, open the liquid and the suc-
tion line service valves fully. Turn the stem of the liquid service
valve clockwise
1
/
4
turn to open its access port for reading pres-
sure.
Start the compressor (after 8 hours of crankcase heat), turn the
stem of the suction line service valve clockwise 1/
4
turn to open
its service port and continue to charge refrigerant gas through
this suction access port until you meet the conditions shown on
the charging curve, Fig. 7
.
Open the liquid and vapor line service valves fully to close their
access ports after the system has been charged.
First Stage of Cooling
All units employ a cooling lockout switch that does not allow
compressor operation below 40ºF ambient. When the ambient
temperature rises above 50ºF and there is a call for cooling at
terminal Y1, RY1 relay is energized closing the RY1-1 con-
tacts. RY1-1 energizes time delay 3TR. When the time delay
relay 3TR is satisfied as described below, it will energize its out-
put terminal Y2, which is connected to terminal 7 of lockout re-
lay (OR = Lockout Relay operation is discussed below).
LOR-1 will power the low pressure switch (LP) circuit, high
pressure switch (HP), compressor 1 contactor coil (1M) and the
condenser fan 2 contactor coil (3M) through the condenser fan
cycling switch (PSC). The condenser fan cycling switch (PSC)
will cycle condenser fan 2 based upon the discharge pressure
of the system. PSC closes at 320 PSI and opens at 180 PSI.
Anti-short Cycle Time Delay Relays 3TR and 4TR
Relay 3TR, which serves compressor 1 control, has an adjust-
able low voltage lock out which is set at 20V in the factory. The
voltage applied to 3TR must be above its lock out setting and 5
minutes must elapse since the relay was last energized before
it will energize its output terminal Y2. Relay 4TR is identical but
it serves compressor 2 control.
Low or High Pressure Lock Out Operation
If the lock out circuit path is opened during a call for cooling, the
lock out relay (LOR) coil will energize, opening LOR-1 contacts
and disabling all compressor operation. The lock out circuit
path is open if:
•
the lock out relay contacts LOR-1 are open, OR
•
the low pressure switch LP is open AND the low pressure
switch bypass timer contacts 1TR-1 are open, OR
•
the high pressure switch HP is open.
Once the LOR coil has been energized, it remains energized,
locking out cooling operation until the call for cooling has been
removed. When Y1 is returned to 0 volts, the LOR coil is no
longer energized, closing the LOR-1 contacts and removing
the lock out.
The low pressure bypass timer 1TR leaves the 1TR-1 contacts
closed upon the start of a call for cooling until its 90 second
(nominal) timer has expired. This bypasses the low pressure
switch during start up. After the time delay has elapsed, 1TR-1
contacts are opened, once again allowing low pressure to trig-
ger the lock out circuit if the low pressure switch opens.
12
Unitary Products Group
035-17393-000 Rev. A (0501)
START-UP
CRANKCASE HEATER
The crankcase heater must be energized at least 8 hours before
starting the compressor. To energize the crankcase heater, the
main disconnect switch must be closed. During this 8 hour peri-
od, the system switch on the room thermostat must be “OFF” to
prevent the compressor from starting.
CAUTION: DO NOT ATTEMPT TO START THE COMPRES-
SOR WITHOUT AT LEAST 8 HOURS OF CRANK-
CASE HEAT OR COMPRESSOR DAMAGE WILL
OCCUR.
Make sure that the bottom of the compressor is warm to the
touch to prove crankcase heater operation.
PRE-START CHECK
Before starting the unit, complete the following check list:
1. Have sufficient clearances been provided?
2. Has all foreign matter been removed from the interior of the
unit (tools, construction or shipping materials, etc.)?
3. Have the condenser fans been rotated manually to check for
free rotation?
4. Are all wiring connections tight?
5. Does the available power supply agree with the nameplate
data on the unit?
6. Is the control circuit transformer set for the proper voltage?
7. Have the fuses, disconnect switch and power wire been
sized properly?
8. Are all compressor hold-down nuts properly secured?
9. Are any refrigerant lines touching each other or any sheet
metal surface? Rubbing due to vibration could cause a re-
frigerant leak.
10. Are there any visible signs of a refrigerant leak, such as oil
residue?
11. Is any electrical wire laying against a hot refrigerant line?
INITIAL START-UP
1. Supply power to the unit through the disconnect switch at
least 8 hours prior to starting the compressor.
2. Move the system switch on the thermostat to the AUTO or
COOL position.
3. Reduce the setting of the room thermostat to energize the
compressor.
4. Check the operation of the evaporator unit per the manufac-
turer's recommendations.
5. With an ammeter, check the compressor amps against the
unit data plate.
6. Check for refrigerant leaks.
7. Check for any abnormal noises and/or vibrations, and make
the necessary adjustments to correct (e.g. fan blade(s)
touching shroud, refrigerant lines hitting on sheet metal,
etc.)
8. After the unit has been operating for several minutes, shut
off the main power supply at the disconnect switch and in-
spect all factory wiring connections and bolted surfaces for
tightness.
OPERATION
