How to Diagnose & Repair Air Conditioner Compressor Hard Starting InspectAPedia® -
Air conditioning compressor hard-starting
How to diagnose air conditioner start-up problems
Air conditioner stutters or makes noises at start-up
When to install a hard-start air conditioner repair kit with starting capacitor
Hard starting can indicate end of air conditioner life, or it may be just a small repair
Air conditioner compressor defect diagnosis & repair guide
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HARD STARTING - How to Diagnose & Repair Air Conditioner Compressor Hard Starting
Stuttering or on-off at startup: A "hard starting" compressor may stutter or begin to cycle-on then stop, then restart.
If a compressor is frequently tripping the
circuit breaker (or blowing the fuse) which protects its circuit, compressor and wiring diagnosis and repair are needed.
Low line voltage: Abnormally low line voltage may also be causing a compressor to "hard start". Air conditioner
supply voltage is typically checked using a VOM (voltage ohms meter) right at the air conditioner service disconnect box near
the compressor/condenser unit. Voltage should be within 10% of the required number (on the compressor/condenser data tag). A
service technician may also check line voltage again at the compressor terminals when the compressor has reached normal
operating state to be sure that there is no voltage drop.
Starting an air conditioner against compressor head-pressure:
When an air conditioning compressor has been running long enough to reach its normal operating condition,
it has pumped refrigerant to a high pressure condition in the compressor head.
When an A/C system compressor is running and is unexpectedly shut off, perhaps by a human testing a thermostat or switch, if the system
is immediately turned back on, some compressors, particularly older window and wall units, may be unable to re-start against this high
head pressure. Simply waiting a few minutes for pressures to equalized may be all that's needed. So if the compressor is not starting
in this condition we simply turn it off and wait. If this problem is happening often, a service technician may install one of several
versions of "hard start kit".
Do not just install a larger fuse
or circuit breaker as doing so risks a fire or equipment burn up. Do not bypass fuses such as by installing
copper tubing in place of fuses as some A/C service people recommend. This is a crazy electrical hazard risking fire, shock,
and equipment burn-up. If new circuit breakers are to be installed to replace an older fuse-protection on an air conditioning
circuit, the electrician should remove any obsolete, unused electrical equipment or devices to avoid future confusion or possible shock hazards.
A "hard start kit" is basically a capacitor which
gives an extra electrical "jolt" to the compressor motor to get it moving. A starter relay may also need to be installed or replaced.
Some air conditioning compressor brands do not usually need a hard start kit. GE, Trane, and Manurope are examples that do not usually
take this kit. See CAPACITORS for HARD STARTING MOTORS for photos, wiring diagram, and installation instructions for air conditioner compressor, fan, blower, refrigerator motor, freezer motor, or other electrical motor starting booster capacitors.
Bad air conditioner starting capacitor: your air conditioning compressor may already have a starting capacitor installed, but the starting capacitor itself may have failed. While electric motor starting capacitors can fail in a variety of ways that may not be obvious without performing some electrical tests, on occasion the failed starting capacitor may be visually obvious.
Most electric motor or compressor starting capacitors used on air conditioning equipment are in a round cylindrical shape. The two ends of the cylinder should be flat. If your starting capacitor is visibly bulged at its end(s) or anywhere else, or if it looks split or burned, it's almost certainly damaged and needs replacement. But beware: other problems can cause the starting capacitor to fail, and some starter capacitor failures may not be visibly apparent. If your starting capacitor is replaced and fails again, further diagnosis of the failure source is needed.
See CAPACITORS for HARD STARTING MOTORS. There we also comment thatin addition to hard starting or a non-starting air conditioner or heat pump compressor motor, a bad starter capacitor can also disable the fan in the outdoor compressor/condenser, or the blower fan in the indoor air handler unit. Thanks to reader George Fazio for this air conditioner start-up diagnosis suggestion and for the photo of an un-damaged starter capacitor (above left).
Tight or Seized Air Conditioner Motors can be hard to start and may make a "humming" noise while trying to start-up and
the compressor motor may fail to start at all, eventually tripping the circuit breaker or blowing the circuit fuse.
It might be possible to get a slow or hard-starting tight or even seized AC compressor motor going again
- see TIGHT or SEIZED AC COMPRESSORS for more details on how this is done.
But in any case such a compressor is probably near the end of its life.
End of air conditioning compressor life may be near: A compressor which has difficulty starting might be fixed by installing a "hard start" kit,
but depending on the reason for hard starting it's possible that the entire compressor will have to be replaced soon.
On a more optimistic note, some hard start kit manufacturers assert that installing a "hard start kit" on a compressor will extend its life.
"By assisting the compressor in starting at up to ten times faster than normal, Kickstart(R) hard start devices significantly reduce
the amount of damaging heat that is generated in the motor windings with each and every start. Over time, this reduced stress on insulation,
wiring, and other critical components of the compressor has the effect of increasing its reliability and extending its useful life." -- www.kickstartoem.com
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"Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
ALUMINUM WIRING HAZARDS - aluminum electrical wiring often burns-up at high-amperage electrical connections such as air conditioner wiring.
Federal Pacific Electric (FPE) FPE Stab-Lok Circuit Breakers can increase the risk of a fire if these breakers are used on air conditioning or heat pump equipment
Zinsco Electrical Circuit Breakerss: overheating, failure to trip, burn-ups involving Zinsco and certain Sylvania electrical panel components. These components can also increase the risk of a fire if these breakers are used on air conditioning or heat pump equipment
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