Heat pump outside unit only works when contactor manually pressed
I have Brynt (16 yr old) heat pump system. It was running fine few days ago, and all the sudden outside unit quit responding to the thermostat. When put on heat, the inside fan will run, but the outside unit (fan and compressor) does not turn on. It seemed like it is not getting any power, so I took the cover off, and checked if it (unit) is getting the power. The contactor is getting the power, and the unit runs, when contactor is manually pressed. As soon as I release the button, it stops running. I have checked the thermostat wiring to best of my abilities and they seem to be right (plus unit was working fine with the current wiring few days ago). Apparently contactor is not being pulled when put on heat or on cold; it (outside unit) does not respond to any setting on thermostat. I had my system checked by tech few days ago, because it was frosting, he manually defrosted the unit (test pins), and it ran fine; he told me that I should change the board, and I did. The feron level is fine as he tested few days ago, and everythign was running well. All the sudden outside unit does not respond.
I am completely new to the forum, and the heat pump system. I need to replace the unit (pretty old, and want to increase the capacity), so I figure it is good time for me to learn the system (even if I mess up, it needs to be changed, and if I can fix I can hold on to buying new unit for few more months). If any one knows the solution, please provide step by step instructions (I am completely new to the system). Thank you so much in advance.
Comment on Theaircoguy's post
Sorry, never mind this answer. I forgot you said it comes on when you push the contactor. That rules out the capacitor theory.
Comment on Theaircoguy's post
From what I tested, no I am not getting any voltage on the contactor coil. This could be because I am not checking the voltage properly or at the right wires. Could you please tell me, which wires and how to check the voltage on that with volt meter? Sorry, completely new to this stuff. I am getting voltage from the source (with ground 124V each and between them 248V; black and white wires at the bottom of contactor); I got two wires going from the left side of contactor Red (124V; measured to ground), and Black (124 V; measured to ground); At the top of contactor I have four wires two black and two yellow (all of them have 124V, measured to ground); now the right side, which I think is the coil side of contatcor (not sure), has three wires Brown, yellow, and yellow (none of them have any voltage; again I am measuring with ground); My ground being the metal case. My capicotrs look in good shape.
Comment on Theaircoguy's post
Just for reference here are pics of My contactor, and defrost board wiring.
http://postimage.org/image/1ynn4a9pg/
http://postimage.org/image/1yolukk2s/