Hi my abandoned central AC from the side of my garage is running 240v on 40amp circuit. My electrician just installed a 50 amp receptacle outlet outside by my garage wall. Would it be fine charging with the nema 14-50 on 40 amp circuit ?
Yes; the NEC allows for installing a NEMA 14-50 receptacle on a 40A circuit (usually in cases where there is insufficient capacity for a 50A circuit.) If the condition of the existing wire is determined by the electrician to be good then the 14-50 receptacle can be used. The receptacle should be labeled 240V/40A so there is no confusion as to the maximum rating of the circuit.
A better option would be to install the Tesla Wall Connector on the side of the garage instead of the 14-50 receptacle. The Wall Connector is designed for use in all weather conditions. Even with a weather housing it is possible for water and moisture to get into the connection between the NEMA 14-50 receptacle and the 14-50 plug.
The Tesla Wall Connector now comes with a 24 ft charging cord so it might be able to reach the Tesla vehicle's charging port without having to back the Tesla vehicle onto the driveway. The Wall Connector can be set to operate on any circuit rated from 15A up to 60A so it could be set to 40A for use on the existing circuit.
I have an 18' cord on my Wall Connector that is mounted at 5' -- I can pull into the driveway, and it reaches without any problem. It doesn't drag on the ground and it seems that the strain relief on the charge end has plenty of support.
And as jcanoe stated "A better option would be to install the Tesla Wall Connector on the side of the garage instead of the 14-50 receptacle. The Wall Connector is designed for use in all weather conditions. "