Another side effect is the potential to increase the temperature of the indoor coil, reducing the dehumidification of the indoor air; an important benefit of conditioned air. The air in your home will likely feel sticky or muggy as a result.
The potential for the greatest amount of damage, though, is to the compressor. Overcharging the unit can cause permanent failure of the compressor, which is the pump for the refrigerant. Replacing the compressor can actually cost more than replacing the entire outdoor unit.
Some air conditioner systems have an automatic shutoff if the internal circuitry determines the system has been overcharged, which could help minimize the damage. When this happens, though, the system will power down and must be reset and the overcharged refrigerant removed before it will power back on. So expect to still require the services of a technician if your system does automatically shut off.
The larger question here is why your technician added so much refrigerant to begin with. First off, if the technician suspected a coolant leak, he or she should have performed a leak test before adding any R-22. As you likely know, the cost of R-22 refrigerant is rising quickly as Freon is being phased out because of its ozone-depleting properties. Homeowners are paying three and four times the cost of R-22 as they were just a few years ago. No longer is it financially feasible — or environmentally responsible — to simply ignore a leaking unit and recharge it with more refrigerant.
RELATED: What is a Fair Price for R-22?