I am slowly accumulating information and knowledge about home HVAC system. Earlier on, I have a failure to start problem and it turns out to be a bad thermostat diagnosed by a friend.

General concept and knowledge about home HVAC system
This post provides basic knowledge about electricity.

Here are some possible items to document, 15 videos of maintenance tips

He suggests 15 maintenance tips to perform to maintain the system

1.	Uncover the unit
2.	Cleaning condensing coil
3.	Check wire and components
4.	Check the capacitor
5.	Check the suction line cover
6.	Level the base 
7.	Turn AC on earlier
8.	Check the fan – kick start
9.	Check the temperature drop
10.	--

	
Spray cleaning the unit thoroughly

Basic wiring diagram for HVAC system
There are many online service tech resources, I have found a few very good tutorials

The clean one is AC service tech llc on the home HVAC service board and wiring.
This guy explains the wiring to HVAC very well, I want to give me a thumb up.
And, he drew a very good diagram.
Checking the power to the thermostat.
Another guy makes an interesting little device to show the wiring diagram!
He has an earlier video on this device, which explains the same concept.
It turns out that he has a series of such device, this time it illustrates the "coil" function.
Another post on a dummy digram also illustrates the connection and how they can fail. He lists out relevant books, more videos and tools to test the system and fix the problem.

Google nest learning thermostat

My friend has a failure, I need to understand the basic Google Nest Learning Thermostat
It turns out that yoububer does a better job explaining it.

Check the compressor

Fan motor is not working, this guy provides a very general video but does not give very instructional step by step. I need to research more on it. 
I like his post
He puts out a very clear capacitor testing video as well. I think I still need a wiring diagram.
Normally, there are two capacitors that power the outdoor condenser and condenser fan/motor like this 
Someone says this way is not a good way
Chris does not like the above video.

Here is another hand drew diagram

Check the furnace

All about capacitor fails
I found this post extremely helpful.

There are three major connections: labeled as C-connector, HERW, and fan. Like the follow figure shows.
top connection.

These three connection points can be identified by the number of tines, revealed by the following diagram



4-tine common (black), 3-tines HERM (white) and 2-tines Fan (Green). In our system, there was one wire connected to the fan, two different color wires to the common, and two red wires to HERM. Referring to the following diagram.



I found another post on how to wire these component with a duo capacitor. The wire is different from our system though, we have two wires go to HERM.