A/C blows cool at idle, but warm when in motion

[bbacon05]

I did a search for this and was unable to find much information, I have a 98 Explorer 5.0L and when I'm stopped at a light, it blows cold air from the vents, but the second I start moving the air just starts getting warmer and warmer. I do know that there is are very slow leaks at the compressor and the accumulator that's probably why the air at a stop is cool and not cold and I'll be replacing those parts this weekend, I just wanted to see if that might be the cause of the problem, because I would hate the tear the system apart flush it and recharge it to only have a/c working when I'm stopped. So would low refrigerant cause it the air to be cool at idle and not while moving? Or is there another part I should look at before replacing the compressor and accumulator?
Thanks in advance for any help, I don't post much, but have used many of the how-tos to help my explorer make it to the 292,000 miles it has on it now