The Von Duprin QEL motor has a couple features that protect the motor.
If the LED is alternating between Green and Red;
There is a Tamper Resistance feature that will retract the device again if something pulls it out of the retract mode while still powered.
This feature is intended for situations where either a slamming door or a person caused the push pad to extend which would also extend the latch.
If that happens a few times in a short period of time, typically due to a person pulling out the push pad repeatedly, the LED will flash alternating between Green and Red for a period of time (2 minutes for the QEL motors made before December 2014, 15 seconds for motors after December 2014), then reset and retract the latch and push pad.
There is another feature that notices when the motor cannot pull in completely when initially powered.
This is often due to mechanical (vertical rod or mortise finger) adjustment or something blocking the latch or push pad from moving freely (excessive preload on the latch, mangled push bar guides, etc.), but could also happen when someone is pulling on the push pad when the motor tries to retract.
In this case, the motor will attempt to retract a few times (often making a ratcheting sound, like "KERCHUNK-KERCHUNK-KERCHUNK"), then the LED on the motor will be solid red while powered and will not reset until power is dropped to the motor.
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