I just wanted to update on my control board work, so it could benefit someone else in the future.
I did looked around the web for 325878-751 OEM control board. Price varied from $115-350. Lowest I could find was at ebay search. Later I ordered through one of those vendor @ $115. Since I needed to replace control board on both of my ACs, I spent ~$245 for 2 cards(including S&H).
While I was waiting for the part to come, I found the instruction manual for this card at :
I familiarized myself with the instruction, while I was waiting for the card. Replacement card comes with wiring harness and instruction manuals. Some of the steps in the manual may be confusing initially but when you read it along with the circuit diagram (which is usually found at/or inside AC panel door), it is easy to follow. Original AC manual(if you are lucky) also has circuit diagram and lots of useful information in it.
My cards finally arrived yesterday. After work I started working on it and it took ~1hr each for me to finish the replacement. Instead of removing all wires from the broken card(as it says in the instruction manual), I removed wires one by one and connected them to new card. One of the wire from AC door panel switch was short, so I had to make a trip to home store.
After reconnecting all the wires, followed the instruction to short 'COM' to 'TEST'. Boards self-test completed as stated. Closed the door and voila !!!
Both of my ACs are working normal now. It was fun and empowering project for me. And not to mention I saved lot of money. AC companies around here quoted $450-600 to replace one card i.e. >$1000 to replace 2 cards.
Once again thanks 'beenthere' and 'SKIP4661' for your comments.