UNIT OPERATION - 090 & 120 MBH
When the external control calls for cooling at terminal Y1:
1. The system controller (SC) is energized. The system con-
troller starts the compressor and enables the condenser
fan(s) by energizing contactor 1M.
Condenser fan motor #1 is energized with the compressor
on the 10 ton model while fan #2 is enabled with compres-
sor operation. Fan motor #2 operation is controlled through
the Ambient Temperature Switch (ATS) which will de-
energize the motor when the ambient temperature falls be-
low 70
°
F.
2. Safety Lockout: The system controller (SC) has a lockout
circuit to prevent compressor short-cycling on a safety con-
trol with automatic reset. If the high or low refrigerant pres-
sure switches (HP or LP) open, the SC will enter lockout
mode.
SC provides a 90 second bypass of the low pressure switch
LP to prevent nuisance lockouts during unit start-up.
A malfunction light (24V, 2 A max. resistive load) can be en-
ergized through SC, by connecting the light between termi-
nals X and B on TB1. Terminal X will energize when SC
locks out.
NOTE: To reset the unit after a lockout:
A. Turn the system switch on the thermostat to the “OFF”
position and back to the “COOL” position.
OR
B. Increase the set point of the room thermostat above the
temperature in the conditioned space and return it to its
original setting.
If the unit continues to be shut down by one of its safety
controls, service should be called to determine the cause of
the problem. Repeated resetting of the lockout circuit may
damage the unit.
035-15406-002-A-0504
12
Unitary Products Group
CRANKCASE HEATER
The crankcase heaters must be energized at least 8 hours before
starting the compressor. To energize the crankcase heaters, 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 refrig-
erant 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 inspect
all factory wiring connections and bolted surfaces for tight-
ness.
OPERATION
START-UP
