Arrived onsite for ac maintenance on 1 system. Asked customer to turn AC on to confirm operation. Checked all electrical. Chemically Cleaned outside unit, measured pressures for 410a at 121/236psi with 12 degree sub cooling with outside temperature at 70 degrees. Measured temperature drop at 17 degrees. Cleaned evaporator coil and blew out condensate line. System could be 10 percent low on refrigerant. May have trouble keeping up on hotter days. Customer will let us know off system gives them an issue.