Outside unit is on but system not cooling

I have my System looked at every year. I have a spring and fall check up done. Last spring and fall everything checked out fine. Refrigerant was fine. I’ve had the fan motor replaced 3 years ago and my capacitor replaced about 2 years ago. The other day it was un seasonably warm out and my house reached 76. I wanted to cool it to 73 so switched my thermostat from off to cool. About 4 hours later I noticed my temp was still 76. This is the first time I’ve put the unit in cool mode since last fall. The unit is running outside. There doesn’t appear to be any oil(refrigerant) outside near the unit that would indicate a leak. I have a technician coming this Friday but if there are things that I can check first to save me a service visit that’d be great.

Another question. I understand this question could be really broad but I just wonder in the situation I’m in with the same symptoms I’m having, what is usually the most common issue causing the system not to cool.

Also before I forget, The system is 10 years old and it’s a Carrier.