Traced the blue gunk coming from behind my fridge and it's finally explained

Had almost the same scare with our Whirlpool about three years ago. Found this sticky bluish crust on the floor pan under the back of the fridge and I was sure the compressor gaskets were leaking oil, which is basicly a death sentence for a fridge. I even had a repair guy quote me for a new compressor before I wiped the area with a damp cloth and realized the stuff had a faint sweet smell, like old antifreeze, and it was only showing up after I ran water through the door dispenser.

Turned out the shutoff valve under the kitchen sink had a slow seep at the packing nut. Every time I filled a glass the pressure bumped up and a drop or two would travel along the outside of the line, picking up dust the whole way down to the back of the fridge where it dried into that gross blue looking film. The blue itself was mostly lint and dust cake mixed with the mineral residue from our hard water, which runs heavy on iron here in central Ohio.

I snugged the packing nut about a quarter turn, laid a dry paper towel under the valve for a week to confirm it was dry, and the mystery crud never came back. Fridge is still running fine on the original compressor, so if your machine cools normally and makes ice, the color on the wall is probaly coming from somewhere boring like mine was.

Chasing stains like that drove me nuts for months on our GE side-by-side. Mine turned out to be coming from higher up than I ever thought to look, which is why I kept missing it. I finally taped a strip of paper towel vertically along the wall behind the fridge and left it for a few days. The stain trail on the paper showed the moisture was running down from about knee height, not seeping out at floor level where I kept finding it. Turns out the shutoff valve for the ice maker line, which sits in the basement ceiling right below the kitchen, had a weepy packing nut. Water traveled along the outside of the copper, wicked down thru a gap in the floor, and picked up mineral and dust on the way, drying to a wierd pale blue crust near the fridge. Tightened the nut a quarter turn and it stopped for good. The paper towel trick sounds dumb but it saves you from cleaning the same spot over and over while the real source stays hidden. For the stain itself on my baseboard, a paste of baking soda and a little water lifted it after the vinegar wash alone wouldn't touch it. Worth checking anything above or behind the fridge, not just the fridge parts themselves.

This thread is making me look at my own fridge differently. I've got a weird grayish smear down there behind mine and I always figured it was just dust that got damp somehow. Never thought about water traveling along the outside of a tube like that. So the blue stuff in your case was basically that paste they use when joining pipes togather? I've seen my dad use something like that once but had no idea it stays colored. Does it keep seeping out forever or does it eventually dry up and stop once the joint is done?

I found that in several cases where the stain persists despite verifying the ice maker line is secure, the issue is often related to the proper drainage of internal condensation. Even if the appliance appears to be functioning normally, if the condensation pan inside the unit is clogged or improperly routed, that excessive moisture can track down the exterior of the frame and onto the rear housing, mimicking a leak. You must verify that the entire cooling system is seated level, as even a slight tilt can cause drainage to pool rather than escape. This paticular type of structural overflow can create a similar appearance to the mineral residue you described, requiring a deep clean of the internal components rather than just external patching.

I always thought the white stuff behind my fridge was just dust or some light condensation from the cooling process. It's more of a chalky film, totally diferent from the blue stain everyone is talking about. My fridge doesn't even have an ice maker, so I don't think the water line is the source. I'm wondering if my compressor area could just be getting damp or foggy when the unit kicks on? I'm worried the parts are collecting moisture, even if they don't seem to be actively leaking.