The AC is not blowing cool air intermittently. AC runs fine during the night and morning, at around afternoon and evening cool air stops coming from the vents. When it first happened I turned the thermostat to off and turn off the breaker inside the air handler and the one labeled AC for the main circuit breaker panel. After around 30 mins I switched it back on and it operated normally. It started to happen in the night and not only the day anymore. At first I thought it was capacitor however after doing some searching online I started to look at the contactor. I opened the panel on the outside unit and watched the contactor during normal operation. The contactor was shut and everything was ok, after sometime it stopped cooling again so I went to the contactor and it is was open. It was not pushed in like how it was when it is working correctly. The air handler inside runs and the fan on the outside unit is running. However, I don't hear the compressor running. What could cause the contactor to open in the middle of operation like that? Is the contactor bad or is there something preventing damage that opens up the contactor?

I am a home owner. 17 year old 10 SEER Rheem 2 ton. Freon leaks. Service engineer found leaky service valve, the one with snap ring. Schraeder valves may leak, too, but they are minor in repair cost. QUESTION: I don't want to spend hundreds of dollars on this old system. How would you advise? Thank you.