Hi, my hvac system is a bit old, my main problem right now is that when the thermostat kicks in and starts the cool cycle, the fan starts as expected BUT... the fan condenser outside is not starting just doing a humming noise, like it is stuck, well yesterday I tried to figure out and manually give it a "push" and it got going like nothing... so everything went perfect, but today its not starting again, what does it need to be replaced?. the motor fan?. or is there anything else that might be affecting my system?

There is probably a motor starting capacitor that has worn out. Trace the wires from the fan motor and see if you see a round or oval can with several push-on connections. Replace with an equivalent part. Should be a $20 part or so.

Make sure you disconnect the power before doing this work!

Best of luck,
WallyH

Thanks a lot for your answer!. found out it's a 40+5 capacitor and already ordered it, will give it a try...
What should the reading on the terminals be for?. I haven't looked at it yet.. but noticed one has a C the one is 2 posts and another 3.. something like that...
But what should I prepare for?

The capacitor is actually 2 capacitors in a single can. In your case one is 40 uF and one is 5 uF. One of the capacitors goes to the compressor motor and the other goes to the fan motor. Hopefully you have not yet removed the wires from the old one so that you can simply transfer them one at a time from the old to the new.

For your information, the "C" terminal means "Common". This terminal is connected to both the fan and the compressor motors. That is, each motor will have 2 wires going to the capacitor can, and one from each motor will go to the Common terminal. The other wire from each motor will go to its respective 40 uF or 5 uF connection.

Generally, the 5 uF side will go to the fan motor and the 40 uF side will go to the compressor. A lot of times, the terminals will be labeled, "Common (C)", "Fan (F)", and "Herm (H)". Herm is short for hermetic, or the hermetically sealed compressor.

Here are a couple of good websites for reference:
Air Conditioner Dual Motor Start Capacitor Replacement Instruction Guide With Pictures
Capacitors

I hope this information is helpful,
WallyH