Not 100% sure
New dryers are 4 prong
Older dryers were 3
Same for stoves

Most of the appliances that use 220 also have 110 circuits for the clock, and controls. In the past you would get the 110 off one leg and the ground, now with 4 prong you have a neutral and ground.

So 3 prong outlet was correct, but should be changed to 4, if possible, may only have 3 wires.
It does not HAVE be be changed to 4. but would be better as 4.

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Rick Cantrell
Columbus GA