34
START-UP
Unit Preparation —
Make sure that unit has been in-
stalled in accordance with these installation instructions and
applicable codes. Ensure Start-Up Checklist on back page of
booklet is completely filled out.
Return-Air Filters —
Make sure correct air filters are in-
stalled in unit (see Table 1). Do not operate unit without return-
air filters.
Outdoor-Air Inlet Screens —
Outdoor-air inlet screen(s)
must be in place before operating unit.
Compressor Mounting —
Compressors are internally
spring mounted. Do not loosen or remove compressor hold-
down bolts. Remove the tiedown bands that hold the compres-
sors together on 50TFF014 units.
Internal Wiring —
Check all electrical connections in
unit control boxes; tighten as required. Verify and correct if
necessary. Ensure that electrical component wiring does not
come in contact with refrigerant tubing or sharp edges.
Refrigerant Service Ports —
Each refrigerant sys-
tem has 4 Schrader-type service gage ports: one on the suction
line, one on the liquid line, and two on the compressor dis-
charge line. Be sure that caps on the ports are tight.
HIGH FLOW REFRIGERANT VALVES — Two high flow
valves are located on the hot gas tube coming out of the com-
pressor and the suction tube going into the compressor. Large
black plastic caps identify these valves. These valves have
O-rings inside which screw the cap onto a brass body to pre-
vent leaks. No field access to these valves is available at this
time. Ensure the plastic caps remain on the valves and are tight
or the possibility of refrigerant leakage could occur.
Compressor Rotation —
On 3-phase scroll compres-
sor units, it is important to be certain compressor is rotating in
the proper direction. To determine whether or not compressor
is rotating in the proper direction:
1. Connect service gages to suction and discharge pressure
fittings.
2. Energize the compressor.
3. The suction pressure should drop and the discharge pres-
sure should rise, as is normal on any start-up.
If the suction pressure does not drop and the discharge pres-
sure does not rise to normal levels:
1. Note that the evaporator fan is probably also rotating in
the wrong direction.
2. Turn off power to the unit, tag disconnect.
3. Reverse any two of the unit power leads.
4. Turn on power to the unit.
The suction and discharge pressure levels should now move
to their normal start-up levels.
NOTE: When the compressor is rotating in the wrong direc-
tion, the unit makes an elevated level of noise and does not
provide cooling.
Cooling —
To start unit, turn on main power supply. Set
system selector switch at COOL position and fan switch at
AUTO. position. Adjust thermostat to a setting below room
temperature. Compressor starts on closure of contactor.
Check unit charge. Refer to Refrigerant Charge section on
page 36. Unit must operate a minimum of 10 minutes before
adjusting charge.
Reset thermostat at a position above room temperature.
Compressor will shut off.
TO SHUT OFF UNIT — Set system selector switch at OFF
position. Resetting thermostat at a position above room
temperature shuts unit off temporarily until space temperature
exceeds thermostat setting.
Heating (If Accessory Electric Heater is
Installed) —
To start unit, turn on main power supply.
Set thermostat at HEAT position and a setting above room
temperature, and set fan at AUTO. position.
First stage of thermostat energizes the first-stage electric
heater; second stage energizes second-stage electric heater ele-
ments, if installed. Check air supply grille(s) to ensure proper
heat supply.
If unit does not energize, reset limit switch (located on
evaporator-fan scroll) by pressing button located between ter-
minals on the switch.
TO SHUT OFF UNIT — Set system selector switch at OFF
position. Resetting heating selector lever below room tempera-
ture will shut unit off temporarily until space temperature falls
below thermostat setting.
Safety Relief —
A soft solder joint in the suction line at
the low-pressure service port provides pressure relief under ab-
normal temperature and pressure conditions.
Ventilation (Continuous Fan) —
Set fan and system
selector switches at ON and OFF positions, respectively. Evap-
orator fan operates continuously to provide air circulation.
Operating Sequence
COOLING, UNITS WITHOUT ECONOMIZER — When
thermostat calls for cooling, terminals G and Y1 are energized.
The indoor (evaporator) fan contactor (IFC), outdoor fan con-
tactor (OFC), and compressor contactor no. 1 (C1) are ener-
gized and evaporator-fan motor, condenser fans and compres-
sor no. 1 start. The condenser-fan motors run continuously
while unit is cooling. If the thermostat calls for a second stage
of cooling by energizing Y2, compressor contactor no. 2 (C2)
is energized and compressor no. 2 starts.
HEATING, UNITS WITHOUT ECONOMIZER (If Optional
or Accessory Heater is Installed) — Upon a call for heating
through terminal W1, IFC and heater contactor no. 1 (HC1) are
energized. On units equipped for 2 stages of heat, when addi-
tional heat is needed HC2 is energized through W2.
COOLING, UNITS WITH DURABLADE ECONO-
MIZER — When the outdoor-air temperature is above the
OAT (outdoor-air thermostat) setting and the room thermostat
calls for cooling, compressor contactor no. 1 and OFC (out-
door-fan contactor) are energized to start compressor no. 1 and
the condenser-fan motors. The evaporator-fan motor is ener-
gized and the economizer damper moves to the minimum posi-
tion. Upon a further call for cooling, compressor contactor
no. 2 will be energized, starting compressor no. 2. After the
thermostat is satisfied, the damper moves to the fully closed
position.
When the outdoor-air temperature is below the OAT setting
and the thermostat calls for cooling, the economizer dampers
move to the minimum position. If the supply-air temperature is
above 57 F, the damper continues to open until it reaches the
fully open position or until the supply-air temperature drops
below 57 F.
When the supply-air temperature falls to between 57 F and
52 F, the damper will remain at an intermediate open position.
If the supply-air temperature falls below 52 F, the damper will
modulate closed until it reaches the minimum position or until
the supply-air temperature is above 52 F.
If the outdoor air alone cannot satisfy the cooling require-
ments of the conditioned space, economizer cooling is integrat-
ed with mechanical cooling, providing second-stage cooling.
Compressor no. 1 and the condenser fan will be energized and
the position of the economizer damper will be determined by
the supply-air temperature. Compressor no. 2 is locked out.
Summary of Contents for 50TFF008-014
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