System Cleanup After Burnout - Carrier R-22 Application Manual And Service Manual

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POWER OFF!
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OHMMETER
0-10 SCALE
1
2
5.2
0.6
2
3
To determine if any winding has a break in the internal wires and
current is unable to pass through:
1. Be sure all power is off.
2. Discharge all capacitors.
3. Remove wires from terminals C, S and R.
4. Check resistance from C-R, C-S and R-S using an ohmmeter
on 0-1000 ohm scale.
Because winding resistances are usually less than 10 ohms, each
reading appears to be approximately 0 ohm. If resistance remains
at 1000 ohms, an open or break exists, and compressor should be
replaced.
Be sure internal line-break overload is not temporarily open.
GROUND CIRCUIT
To determine if a wire has broken or come in direct contact with
shell, causing a direct short to ground:
1. Be sure all power is off.
2. Discharge all capacitors.
3. Remove wires from terminals C, S, and R.
4. On hermetic compressors, allow crankcase heaters to remain
on for several hours before checking motor to ensure windings
are not saturated with refrigerant.
5. Use an ohmmeter on R X 10,000 ohm scale. A megohmmeter
may be used in place of ohmmeter. Follow manufacturer's
instructions.
6. Place 1 meter probe on ground or on compressor shell. Make
a good metal-to-metal contact. Place other probe on terminals
C, S, and R in sequence.
7. Note meter scale.
8. If reading of zero or low resistance is obtained, motor is
grounded. Replace compressor.
A compressor of 1–ton capacity or less is probably grounded if
resistance is below 1 million ohms. On larger-sized, single-phase
compressors, resistance to ground should not be less than 1000
ohms per volt of operating voltage.
Example:
230 volts X 1000 ohms/volt = 230,000 ohms minimum
(EXAMPLE)
TO DETERMINE INTERNAL CONNECTIONS OF SINGLE-
PHASE MOTORS (C,S,R) EXCEPT SHADED-POLE
DEDUCTION:
1 3 (GREATEST RESISTANCE)
2 3 (SMALLEST RESISTANCE)
1
1 2 (REMAINING RESISTANCE)
5.8
3
Fig. 28—Identifying Internal Connections
5.8 (OHM)
0.6
5.2
SHORT CIRCUIT
To determine if any wires within windings have broken through
their insulation and made contact with other wires, thereby
shorting all or part of the winding(s), be sure the following
conditions are met:
1. Correct motor-winding resistances must be known before
testing, either from previous readings or from manufacturer's
specifications.
2. Temperature of windings must be as specified, usually about
70°F.
3. Resistance-measuring instrument must have an accuracy
within ± 5-10 percent. This requires an accurate ohmmeter,
such as a Wheatstone bridge or null balance-type instrument.
4. Motor must be dry or free from direct contact with liquid
refrigerant.
MAKE THIS CRITICAL TEST
(Not advisable unless above conditions are met.)
1. Be sure all power is off.
2. Discharge all capacitors.
3. Remove wires from terminals C, S, and R.
4. Place instrument probes together and determine probe and
lead wire resistance.
5. Check resistance readings from C-R, C-S, and R-S.
6. Subtract instrument probe and lead resistance from each
reading.
If any reading is within ± 20 percent of known resistance, motor is
probably normal. Usually a considerable difference in reading is
noted if a turn-to-turn short is present.
Step 3—System Cleanup After Burnout
Turn off all power to unit before proceeding. Wear safety
glasses and gloves when handling refrigerants. Acids formed
as a result of motor burnout can cause burns.
NOTE: To analyze level of suspected contamination from com-
pressor burnout, use Total Test™. See your distributor/branch.
Some compressor electrical failures can cause motor to overheat.
When this occurs, by-products, which include sludge, carbon, and
27
RUN WINDING (R)
START WINDING (S)
2
IS COMMON (C)
BY ELIMINATION
2
IS COMMON,
THEREFORE, 1 IS
START WINDING (S)
3 IS RUN WINDING (R)
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