SERVICING
21 Rev 1
S-1 CHECKING VOLTAGE
WARNING
Disconnect Electrical Power Supply:
1. Remove outer case, control panel cover, etc. from unit
being 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 the condensing unit
or at the field connections for the air handler or heaters.
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, energize
the unit.
5. Measure the voltage with the unit starting and operating,
and determine the unit Locked Rotor Voltage.
NOTE
: If
checking heaters, be sure all heating elements are en-
ergized.
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 compres-
sor, or to the T
1
and T
2
terminals of the contactor. Start
the unit and allow the compressor to run for several sec-
onds, then shut down the unit. Immediately attempt to
restart the unit while measuring the Locked Rotor Volt-
age.
6. Lock rotor voltage should read within the voltage tabula-
tion as shown. If the voltage falls below the minimum
voltage, check the line wire size. Long runs of under-
sized wire can cause low voltage. If wire size is ad-
equate, notify the local power company in regard to ei-
ther low or high voltage.
REMOTE CONDENSING UNITS
BLOWER COILS
VOLTAGE
MIN.
MAX.
208/230
198
253
115
104
127
NOTE:
When operating electric heaters on voltages other
than 240 volts refer to the System Operation section on elec-
tric 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.
% Voltage
Max. Voltage Deviation
Imbalance =
From Average Voltage X 100
Average Voltage
To find the percentage of imbalance, measure the incoming
power supply.
Example:
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 X = 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
L3
L2
L1
By the voltage readings we see that the imbalance rotated
or traveled with the switching of the incoming legs. There-
fore the power imbalance lies within the incoming power
supply.
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
