What's possible cause for this damp soil (A/C or sprinkler or something else)?

I need some advice on this damp soil next to my outdoor A/C unit.

http://imgur.com/a/qAKJh

The backyard is build on slope hill, walkout basement, I notice this damp soil for a while, about 10 feet long. when it's snow or rain, I expect it's damp, but it's sunny in last couple of days, the outside temperature is about 55-68, and inside is 65. The A/C has not operating yet since last summer. the furnace may run short period of time at night. the sprinkler is winterized.

I monitor the water meter, within 3 hours, the reading remain xxxx.82 gal, can I confidently say there is no leak in the water pipe, or it's simply because water meter is not senstive to detect tiny amount of leaking?

If it has anything to do with HVAC, My understanding is that condensate produced when an air conditioning system is operating (which I am pretty sure A/C is not running). If the damp is related to HVAC, where is the condensate line/pipe?

I google and i saw the condensate line/pipe are in 3 location typically: 1) drain to the bathroom pipe, 2) go to attic, and drip the water from above, 3) penetrate the wall and in the above-ground level. My problem is that I can't locate the condensate line, unless it's buried under ground, and I have dig the soil to see?

Thank you very much for your help!

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