Service Instructions

SERVICING
104
3. Reverse rotation will result in substantially reduced amp
draw from tabulated values.
To correct improper rotation, switch any two power supply
leads at the outdoor unit contactor.
The 3-phase scroll compressors are direction of rotation
sensitive. They will rotate in either direction depending on
the phasing of the power. There is no negative impact on
durability caused by operating 3-phase compressors in
reversed rotation. The compressor's internal protector will
trip, de-energizing the compressor. Continued operation of
3-phase scroll compressors with the rotation reversed will
contribute to compressor failure. All 3-phase scroll com-
pressors should be checked for correct phase rotation.
S-18 TESTING CRANKCASE HEATER (OPTIONAL ITEM)
The crankcase heater must be energized a minimum of four (4)
hours before the condensing unit is operated.
Crankcase heaters are used to prevent migration or accumula-
tion of refrigerant in the compressor crankcase during the off
cycles and prevents liquid slugging or oil pumping on start up.
A crankcase heater will not prevent compressor damage due to a
floodback or over charge condition.
Disconnect ALL power before servicing.
WARNING
1. Disconnect the heater lead in wires.
2. Using an ohmmeter, check heater continuity - should test
continuous. If not, replace.
NOTE: The positive temperature coefficient crankcase heater is
a 40 watt 265 voltage heater. The cool resistance of the heater
will be approximately 1800 ohms. The resistance will become
greater as the temperature of the compressor shell increases.
S-21 CHECKING REVERSING VALVE AND SOLENOID
Occasionally the reversing valve may stick in the heating or
cooling position or in the mid-position.
When stuck in the mid-position, part of the discharge gas from
the compressor is directed back to the suction side, resulting in
excessively high suction pressure. An increase in the suction
line temperature through the reversing valve can also be mea-
sured. Check operation of the valve by starting the system and
switching the operation from COOLING to HEATING cycle.
If the valve fails to change its position, test the voltage (24V) at
the valve coil terminals, while the system is on the COOLING
cycle.
If no voltage is registered at the coil terminals, check the
operation of the thermostat and the continuity of the connecting
wiring from the "O" terminal of the thermostat to the unit.
S-24 TESTING DEFROST CONTROL
To check the defrost control for proper sequencing, proceed as
follows: With power ON; unit not running.
1. Jumper defrost thermostat by placing a jumper wire across
the terminals "DFT" and "R"/"R-DFT" at defrost control board.
2. Connect jumper across test pins on defrost control board.
3. Set thermostat to call for heating. System should go into
defrost within 21 seconds.
4. Immediately remove jumper from test pins.
5. Using VOM check for voltage across terminals "C & O". Meter
should read 24 volts.
6. Using VOM check for voltage across fan terminals DF1 and
DF2 on the board. You should read line voltage (208-230 VAC)
indicating the relay is open in the defrost mode.
7. Using VOM check for voltage across "W"/"W2" & "C" termi-
nals on the board. You should read 24 volts.
8. If not as above, replace control board.
9. Set thermostat to off position and disconnect power before
removing any jumpers or wires.
NOTE: Remove jumper across defrost thermostat before
returning system to service.
S-25 TESTING DEFROST THERMOSTAT
1. Install a thermocouple type temperature test lead on the tube
adjacent to the defrost control. Insulate the lead point of
contact.
2. Check the temperature at which the control closes its con-
tacts by lowering the temperature of the control. Part #
0130M00009P which is used on 2 and 2.5 ton units should
close at 34°F ± 5°F. Part # 0130M00001P or B1370803 which
is used on 3 thru 5 ton units should close at 31°F ± 3°F.
3. Check the temperature at which the control closes its con-
tacts by lowering the temperature of the control. Part #
0130M00085, which is used onunits with 5 mm coils, should
close at 30°F ± 5°F.
4. Check the temperature at which the control opens its contacts
by raising the temperature of the control. Part #0130M00009P
which is used on 2 and 2.5 ton units should open at 60°F ± 5°F.
Part # 0130M00001P or B1370803 which is used on 3 thru
5 ton units should open at 75°F ± 6°F.
5. Check the temperature at which the control opens its contacts
by raising the temperature of the control. Part # 0130M00085,
which is used on units with 5 mm coils, should open at 60°F
± 5°F.
6. If not as above, replace control.
SEQUENCE OF OPERATION
Refer to the installation instructions and wiring diagrams pro-
vided with the MBR/AR*F for specific wiring connections and
system configuration.
MBR/AR*F WITH SINGLE STAGE CONDENSERS
1.0 Cooling Operation
1.1 On a demand for cooling, the room thermostat energizes “G”
and “Y” and 24Vac is supplied to “Y” at the condensing unit
and the “G” terminal on the EBTDR board.