Armstrong HWC PREMIER 122, Service Reference Manual

Page: 189 / 196

9-4
TROUBLESHOOTING Magic-Pak: HW/HWC
SRM-HW/HWC 8/99
When the resistance of “C to S” is added to the resistance of “C to R”,
the combination is the total resistance of the entire motor windings
circuit.
2. Compare the total to the reading taken between “S to R.” If the
windings are in good condition, the sum of “C to S” and “C to R”
should be the same as the reading between “S to R” (S through C to
R). (In this example, they are equal.)
If the numbers are the same, this suggests that the windings are intact
and that there are no internal shorts between the start and run windings.
Example #2
In the following example, the measurements taken provide different
results from the earlier example. These results would indicate that there
is a problem with the compressor.
C to S (Common through Start Windings) 3.5 ohms
C to R (Common through Run Windings) 1.5 ohms
S to R (Start Windings through Common and Run Windings) 4.3 ohms
Using the procedure followed in Example #1:
C to S (3.5 ohms) + C to R (1.5 ohms) = 5 ohms
In this example, the actual reading of “S to R” is 4.3 ohms. In comparing
the readings taken, the resistance measured between “S to R” (the
resistance of the entire motor windings circuit) is not equal to the sum of
“C to S” and “C to R.”
A short between the windings of the start and run coils would reduce the
length of the wire being measured and would result in less resistance
between the two points. Instead of measuring the resistance from “S to C
to R”, the resistance is actually being measured through an internal short
in the windings to the R terminal, bypassing the C terminal. This results
in a lower resistance reading and indicates that the compressor has failed
and the windings are shorted.
Checking the Thermal Overload Device
If during the time that resistance was being checked in the previous test
infinity was ever registered (meter indicated no continuity), the assump-
tion could be made that there is an open winding (or a break in the wires
of the winding). This may indicate that the windings had burned out and
that the compressor had failed.
In the motor windings there is a thermal overload device. This device is
designed to open if the internal temperature of the windings exceed a
preset limit. Since the resistance reading of a winding where the thermal
overload device has opened would show no resistance, the assumption
would most likely be made that the winding was burned out. This is
where the temperature of the compressor as noted in the touch test
becomes very important. If at the time of the touch test the compressor
was found to be very hot, then there is a good chance that the thermal