I noticed that my 2004 Nissan Frontier pickup leaked some refrigerant where the hose from the compressor attaches to a metal pipe on the firewall.  Right now with the engine running I turn on the AC but don't see or hear anything leaking, same thing with AC turned off.  AC is blowing cold air.

I also hear a whinning noise when the engine starts up and have narrowed it down to the idler/compressor.  This noise goes away after a couple of minutes but sometimes when it rains it starts up again, I'm assuming the water gets into this area and causes the noise.

One more thing I did notice some cooling fluid at the bottom of the radiator but not actively leaking, engine temp is also O.K. but then it hasn't been hot lately.

I hope this is not two separate issues, I'm going to try and track down the source at the bottom of the radiator.

Is whinning noise related to leak of refrigerant?  Any ideas on what to look for?

What makes you think there is a refrigerant leak?
Can you tell if you are losing coolant by looking at the reservoir?

Idlers and tensioner pullys can make growling or whining noises,, you can spray wd-40 or something like it into the pulley before you start up to see if that keeps it from happening, that'll tell you if it is the pulley.

If the AC is blowing cold....and it's not cold outside....then it's very unlikely that you have a refrigerant leak.  Also, refrigerant leaks are usually spotted by adding a dye  to the system.  Otherwise, you won't spot a leak.

Do you mean that your cooling system is leaking?  From your description, it sounds more like a cooling system leak than an AC leak.  

Can you post pics?

Part of what I saw is coming out of a line that comes from the AC compressor.  There's a wet stain where the rubber hose connects to a steel pipe/tube at the firewall.  At the same time that I saw this I also saw some coolant (greenish liquid) at the bottom of the radiator but its not dripping out as the engine is running.  The signs are there but as the engine runs nothing is gushing or leaking.  When I return to the house I will get a better look at it and take some pictures.

Got a better look and I'm sure its AC related and since I'm not up to speed on working with a pressurized system I'll just have to take it to a mechanic.  I just wish my go to mechanic hadn't closed his shop, he would have either fixed it or given me a good recommendation for a specialized shop.

Yes you can. The oil in the AC system will make the area "wet" as the OP describes. I'm going with two separate issues although they aren't showing themselves now. OP, clean the areas with oil and coolant well. Run vehicle again and look for fresh leaks.

Could be....but it doesn't take a lot of leakage of refrigerant to stop an AC system from working.  If it's leaking that much, then the AC system shouldn't be working at the moment.

The OP's description doesn't provide enough information to know what's going on.  It's too vague.  Pics would help.  The OP also refers to the idler/compressor....but they are actually two different things.....unless he's getting something confused.

Sounds to me like the OP isn't too familiar with vehicle repair.  That's fine but that contributes to his inability to accurately describe what's going on.  I've learned that sometimes people who are not very mechanically inclined will assume one thing...but when you actually see the issue you discover that it's really something else.  We really don't have nearly enough information from the OP to really know what's going on or to provide him with any more specific recommendations.

Now that I'm back from my out of town dove hunt I can get back to this and where to begin?

Thanks ColtRifle on your gifted insight into my mechanical abilities, have we met?  Aside from changing out the usual alternators, fuel pumps, radiators, oil changes, checking pressure on tires, and kind of knowing which way to turn a screwdriver, no my mechanical abilities are not on par with whoever you think is familiar with vehicle repair.  

That aside sometimes it becomes an issue of being too detailed where the reader is bored and moves on or trying to be succinct in a description and be accused of not giving enough information.

Idler/compressor, yes two different things but when I can trace the whining noise to this area then its one or the other. FYI I adjusted the idlers for the alternator and power steering pump and the noise is not coming from there, ergo.....

The loss of coolant and the separate leak in the AC line while vexing for now I'm sure I'll figure something out.  Thanks and as my boss used to say "NUFF SAID!"

My xterrra a/c compressor, high and low pressure lines gave up the ghost after 9 years and had similar symptoms.

Don't ask for help and then get pissy when people try to help.

Good luck.