* 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 (volt-ohm meter) right at the air conditioner service disconnect box near the compressor/condenser unit. Voltage should be within 10% (5% on 208 volt) 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 speed to be sure that there is no voltage drop.This is known as Running Load Volts (RLV)
* 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 window and wall units,and central units using a resticor type of metering device.Therefore 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 and potential relay which gives an extra electrical "jolt" to the compressor motor.
* 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. 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.