C wire for wifi thermostat

I’m at a loss. I have a wifi thermostat to install. No c wire connected so a 4 wire thermostat but have 4 additional wires unused. I checked our Goodman ac/furnace and found the unused blue wire. The problem I have is there is a wire already attached to the c wire on the unit. I tried adding it so 2 wires inserted and everything worked for about 5 minutes then ac/furnace shut off. No airflow. There was still power on thermostat and showed waiting on equipment. Would attaching a pig tail work?! Uploaded photos. First time I could added the blue c wire and the thermostat powered on and after about 5 min wouldn’t turn on again. Hooked up old thermostat worked. Retried thermostat and did same set and no power to device. I’m at a loss and now this has become a mission to figure out
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