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The antifreeze can and will damage both the pump and the power rack and pinion unit in much the same way as it damages an engine if it gets in the crankcase. The power steering fluid cools and lubricates the internal parts of both the pump and rack and pinion gear. Antifreeze introduced into the system will wash out the power steering fluid from the internal parts and cause damage due to no lubricant.
I would start by replacing the power steering pump to start, but you may have to end up replacing the rack and pinion as well.
Antifreeze is thinner than power steering fluid, so I would assume it is lighter as well. A tiny amount, such as a couple of teaspoons shouldnt damage the system.
The belt shouldnt have any more than 1/8" deflection. You can remove the belt and check the tensioner pulley for binding when turning by hand:
Fig. Loosen the adjusting bolt counterclockwise looking from "A" position and then remove the P/S belt