Came out today for a no ac call for a Lennox ac system. Model #Hs23-411-1p, serial #5193M13493. Upon arrival the homeowner stated that the outdoor unit will not turn on. I called for ac and observed the system starting normally. The indoor unit fired up right away. The condenser unit however would not turn on. I opened the access panel and noted that the contactor was not engaged. I followed the voltage to the low pressure switch. I reset the switch and called for ac again. The pressure switch would not reset. I checked the standing pressures and the high side pressure was .03 and the low side is at 63. The system utilizes R-22 refrigerant which has been phased out. At this time I recommend updating the system to one that utilizes 410-a refrigerant.