Service manual

SERVICING
27
S-1 CHECKING VOLTAGE
WARNING
Disconnect Electrical Power Supply:
1. Remove doors, control panel cover, etc. from unit be-
ing tested.
With power ON:
WARNING
LINE VOLTAGE NOW PRESENT
2. Using a voltmeter, measure the voltage across termi-
nals L1 and L2 of the contactor for single phase units,
and L3, for 3 phase units.
3. No reading - indicates open wiring, open fuse(s) no
power or etc. from unit to fused disconnect service.
Repair as needed.
4. With ample voltage at line voltage connectors, ener-
gize the unit.
5. Measure the voltage with the unit starting and operat-
ing, and determine the unit Locked Rotor Voltage.
NOTE: If checking heaters, be sure all heating ele-
ments are energized.
Locked Rotor Voltage is the actual voltage available
at the compressor during starting, locked rotor, or a
stalled condition. Measured voltage should be above
minimum listed in chart below.
To measure Locked Rotor Voltage attach a voltmeter
to the run "R" and common "C" terminals of the com-
pressor, or to the T
1
and T
2
terminals of the contactor.
Start the unit and allow the compressor to run for sev-
eral seconds, then shut down the unit. Immediately
attempt to restart the unit while measuring the Locked
Rotor Voltage.
6. Should read within the voltage tabulation as shown. If
the voltage falls below the minimum voltage, check the
line wire size. Long runs of undersized wire can cause
low voltage. If wire size is adequate, notify the local
power company in regards to either low or high volt-
age.
UNIT SUPPLY VOLTAGE
VOLTAGE MIN. MAX.
460 437 506
208/230 198 253
NOTE: When operating electric heaters on voltages other
than 240 volts refer to the System Operation section on
electric heaters to calculate temperature rise and air flow.
Low voltage may cause insufficient heating.
Three phase units require a balanced 3 phase power sup-
ply to operate. If the percentage of voltage imbalance ex-
ceeds 3% the unit must not be operated until the voltage
condition is corrected.
Max. Voltage Deviation
% Voltage = From Average Voltage X 100
Imbalance Average Voltage
To find the percentage of imbalance, measure the incom-
ing power supply.
L1 - L2 = 240V
L1 - L3 = 232V Avg. V = 710 = 236.7
L2 - L3 = 238V 3
Total 710V
To find Max. deviation: 240 - 236.7 = +3.3
232 - 236.7 = -4.7
238 - 236.7 = +1.3
Max deviation was 4.7V
% Voltage Imbalance = 4.7 = 1.99%
236.7
If the percentage of imbalance had exceeded 3%, it must
be determined if the imbalance is in the incoming power
supply or the equipment. To do this rotate the legs of the
incoming power and retest voltage as shown below.
L1
L2
L3
L3L2
L1
By the voltage readings we see that the imbalance rotated
or traveled with the switching of the incoming legs. There-
fore the power lies within the incoming power supply.
If the imbalance had not changed then the problem would
lie within the equipment. Check for current leakage, shorted
motors, etc.
L1 - L2 = 240V
L1 - L3 = 227V
L2 - L3 = 238V
Rotate all 3 incoming
legs as shown.
L1 - L2 = 227V
L1 - L3 = 238V
L2 - L3 = 240V