27
COMPRESSOR ELECTRICAL CHECKS
lower resistance and connects directly to the power supply
from the compressor contactor.
2
ˊ
Measure the available line voltage .
A. This could indicate high or low voltage problems or improper start components.
B. check the contactor coil with an ohmmeter for a short or open circuit.
C. Replace the contactor if any fault is noted.
5
.WITH THE ELECTRICAL POWER OFF
, remove all power wires from the compressor
A. Use an ohmmeter set for the highest scale to check for grounding between compressor motor
terminals and a good clean ground such as the compressor shell or copper line.
B. The resistance from any terminal to ground should exceed 1,000,000 ohms.
6.Use an ohmmeter set for the lowest scale and check the continuity of the motor windings .These
ohm values are less than ten ohms and in some cases less than one ohm.
winding has the higher resistance and is connected in series with the
capacitor. The run winding has the
Single-phase compressors use permanent split capacitor motors. There are two windings that
connect at
a common point at the “common” wiring terminal. The two windings are called “start”
and "run". The start
ELECTRICAL CHECK COMPRESSORS
The design uses a protective device called an “internal overload”. If compressor draws high amperages,
for an anusually long time or temperatures in the compressor motor, it opens an internal circuit to stop
the motor.
On the single phase 208/230Volt units ,this should be from 197 to
253 Volts.
1
ˊ
Consult the unit wiring diagram. Confirm that all electrical wiring for the units is correct and that
all wiring connections are right.
3. Check for proper control voltage at the unit contractor coil . If this voltage is inadequate or is not
section for possible causes.
present, refer to the wiring diagram or the compressor troubleshooting flow chart at the end of this
4. Disconnect all power from the unit and visually inspect the compressor contactor for pitted or
burned contacts.
A .The ohm reading from the RUN terminal to common terminal is the lowest reading measured between.
compressor terminals, approxiamtely 1 ohm.
terminals,
MARK THE ORIGINAL LOCATION OF EACH WIRE.
EXAMPLE:
Start to Common -4.0 Ohms
Start to Run -3.0 Ohms
Start to Run -3.0 Ohms
Start to
Common
-
Ohms
B. The ohm reading from the Start TERMINAL TO COMMON TERMINAL will be the middle ohm value
measured between the terminals and be approximately 2.0 to 3.0 ohms
C. The ohm reading from the Start TERMINAL TO Run terminal will be the highest ohm value of the
three measurements and will be approximately the sum of the first two measurements.
A . Run to Common -1.0 Ohms
Conclusion compressor motor does not have open or shorted wincings:
Start to Common -
Ohms
B . Run to Common -
Ohms
CONSLUSION COMPRESSOR COULD HAVE AN OPEN INTERNAL OVERLOAD-
ALLOW THE
COMPRESSOR MOTOR TO COOL AND THE INTERNAL OVERLOAD TO RESET, THEN RETEST.
C. Run to Common -1.0 ohms
Start to
Run
-
Ohms
Central Air Conditioner
Model: Cooling Only,
13
SEER
units
