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I once found an ice blockage in the suction line of a walk-in cooler.

It was a 5 HP R22 system with two evaporator coils tied together and a single 1 1/8" riser with a P-trap at the riser base. The complaint was the box wasn't holding proper temperature.

I don't recall the actual numbers, but it was apparent there was a major restriction between the evaporator outlets and the compressor suction...like 55 psig or so at the evaps and 30 psig at the compressor.

I noticed a distinct sound coming from the area of the P-Trap...almost a whistling noise.

The system had no sightglass/moisture indicator on it, so I installed on and sure enough it showed wet. I then suspected ice as the culprit, so I used a heat gun on the trap and riser, and with the system pumped down drilled a hole in the trap. A several ounces of water and small amount of oil ran out.

It took six drier cores to get rest of the moisture out. To this day, I have no idea why the expansion valves never seemed to freeze up. ???

BTW...This was a fairly new store and my first time servicing it. I know who had done the installation and had run into two other systems they did, both of which had a lot of moisture in them. I made more money fixing their screw-ups than I ever would have trying to compete with them for the install work.

Good point

Originally Posted by HVAC Teacher

Just a guess: oil?
Enough velocity to move it through?
Any sagging, pitch or riser (trapping) issues?

A little sagging as it goes through the cases. Could oil hold back 100+ pounds without moisture? The plug was in the line with three cases feeding it.
For velocity, three 12 foot cases, Hussmann, with three coils in each case, probably 1/4 ton each coil, non-adjustable txv's, sight glass clear at the rack, But the refrigerant level is at the bottom of the receiver. No temp problems noted, but superheat not measured. You bring up a good point.

I have seen some crazy things in suction headers over the years, coke cans, water bottle, but most often as far as numbers, red shop rags. They will sometimes run for years. The weirdest was a rack suction accumulator and the metal plate on the bottom broke loose. It would be sucked up to the tubes, the rack would pump down, shut off and the plate would drop back down and repeat over and over

Just a guess: oil?
Enough velocity to move it through?
Any sagging, pitch or riser (trapping) issues?

plugged up 7/8" line?

Have you ever seen a 7/8" suction line plug up in the middle?
On 5 meat cases on a large supermarket rack with R-22 in operation for ten years. Suction at two of the cases was 35# while at 3 cases it was 100+# (lucky to have a scherader at each case). Have had very few problems on this rack, never a compressor change, very few leaks over the years. The 5 single deck meat cases are tied together with a suction header that starts at 1-1/8" and goes down to 3/4" with no valves in between. I pumped it down. The 100+# cases would not pump down until I started to remove liquid/gas mix from it with hoses. Then all at once it equalized. I cut open the line. It was clean. I changed driers on the rack.
It had happened the week before, but by the time the other tech got there, it had cleared itself, so he just thought it had been stuck in defrost or something. I guess it must have been a wax/moisture glob. But how?