My A/C, while it is cold, isn't as cold as it can be - I get ~55 out of the vents, not ~40. This has been going on since last summer. Yes, I have put the A/C gauges on, and everything checks out there.
I noticed that when put on the max setting, that the heater control valve in the engine bay wasn't pulling its flap shut. I thought that maybe this was because of my A/C mode switch diaphragm, which I have heard hissing for as long as I can remember.
So I changed the diaphragm out yesterday. That made no change in the operation of the heater control valve. I pulled the vacuum line out of the heater control valve, and found that it isn't pulling vacuum.
Not sure how to proceed from here.