An air conditioning contactor staying physically pulled in and refusing to release can be caused by mechanical binding or electrical control faults. A frequent electrical cause is a short-circuited 24-volt low-voltage control wire running from your thermostat to the outdoor unit, which sends a continuous, uninterrupted 24V signal that keeps the electromagnetic coil energized indefinitely. Mechanically, the contactor's plastic plunger or spring mechanism can become jammed due to heavy insect debris, carbon buildup from arcing, or physical warping caused by overheating. Furthermore, a stuck relay on your indoor air handler control board can maintain the 24V loop. You can troubleshoot by disconnecting the low-voltage wires at the contactor. You can verify the cause when removing the 24V signal causes the plunger to drop out; if it stays stuck mechanically, the contactor must be replaced.
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