'03 w/Intermittent A/C

I love the intermittent wipers, but I can't stand my intermittent A/C. I paid about $1000 for the dealer to put a new control unit in just over a year ago, and I now that it's getting warm I noticed it has problems again. The A/C compressor does not always kick in, sometimes I'll be driving for 30-40 minutes before it finally turns on. I'm assuming if the refrigerant was low it would never turn the compressor on, so I'm considering getting a climate control head unit off eBay to try. Does this make sense or is there something else I should check first?

They seem to be going anywhere from $50-100 used. I notice every one I looked at had a different part number, but there were two large letter codes of F145 and F145K. Mine is F145. Is this enough to make a match or do I need to match the exact part number?

There's some good AC guys at LOL, I don't know if we have an AC section at AF, I don't get out much.
I remember some threads on this issue that eventually lead to either undercharge or overcharge. One was a DIY're that added sever cans of refrigerant assuming it was good, then eventually found it was still too low.

Mike may be able to run an XREF for those PN's.. sorry, no help from me.