Walk-In Freezer Drain Line and Drain Heater Problems

A walk-in's drain line is a small copper or PVC pipe that almost nobody looks at until there's ice on the floor. In freezers, it's also one of the most common reasons defrost water refreezes, blocks the pan and ices over the evaporator coil.

What the drain line does

Under every evaporator is a drain pan that catches water from condensation and defrost. A drain fitting at the low point of the pan connects to a drain line that runs out through the wall of the box to a drain outside.

In a cooler, that water stays liquid and just needs a clear path. In a freezer, the water leaves a heated coil and flows through a pan and pipe sitting in sub-freezing air. Without heat, it freezes before it gets out.

How the drain line should be installed

Heatcraft's unit cooler manual sets out the basics:

For heat, the manual calls for a continuously powered drain-line heater on outside traps or runs, at 20 watts per foot for 0°F rooms and 30 watts per foot for −20°F rooms, and says to include the drain-pan fitting on freezers. Those are Heatcraft's figures; other manufacturers publish their own, so check the manual for your unit.

How drain lines fail

Heatcraft's troubleshooting guide lists ice in the drain pan as a possible sign of a defective heater, bad pitch, a plugged drain or a failed drain-line heater. Those are the four things to check.

How a drain problem becomes a coil problem

In a freezer, the chain usually goes like this:

1. The drain line freezes or clogs.
2. Defrost water can't leave the pan, so it refreezes after each defrost.
3. The ice in the pan grows upward into the bottom of the coil.
4. Each defrost melts less of it, and the coil blocks with ice from the bottom up.
5. Airflow drops, the freezer warms, and water or ice starts appearing on the floor and product.

By the time the box warms, the original cause is buried under ice. That's why a freezer with a frozen evaporator coil that's worst at the bottom often turns out to be a drain issue.

Symptoms to watch for

• Water on the floor under or near the evaporator. See walk-in cooler leaking water.
• Ice in the drain pan or icicles hanging from the evaporator.
• Water dripping or spitting from the unit, especially after defrost. See evaporator dripping or spitting water.
• Musty or sour odor from slime in a cooler pan or line. See walk-in cooler smells.
• Ice or water outside the box where the line exits or at the open drain.

Wet floors in and around a walk-in are also a slip hazard. OSHA's walking-working surfaces rule requires floors to be kept clean and, as far as feasible, dry, and free of hazards such as leaks and ice.

Checks staff can do safely

1. Look under the evaporator with a flashlight for water, ice in the pan area, or icicles. Don't climb on shelving to do it.
2. Follow the drain line outside the box to where it ends. Is it discharging into an open drain with a visible gap?
3. Check the outlet end for debris, a crushed section, or ice. Clear loose debris from the open end only.
4. Look for a disconnected or damaged line along the route, including behind shelving.
5. Mop up water and put out a wet-floor sign until the cause is fixed.
6. Note the controller display and whether problems appear after defrost.

Safety: Staff should not reach into the evaporator's drain pan, remove the pan cover, or touch drain heater tape or wiring. Heaters and fans can be energized even when the coil looks off. A technician turns off power at the evaporator before working in the pan.

What a technician will check

A technician will check the drain pan heater and the drain-line heater for continuity and current draw, confirm the line's pitch and trap location, clear the line (often with warm water or a line brush once power is off and the ice is gone), and inspect the pan fitting. If a drain temperature sensor is fitted, they'll check it too. On HTPG's EcoNet controller, for example, a failed drain temperature thermistor shows as alarm A104.

Common fixes include replacing heat tape along the full exposed run and around the pan fitting, re-pitching the line, moving a trap outside the freezer, and cleaning a pan that has built up slime or scale.

Getting it right at installation

Many drain problems are built in on day one: a line run flat to reach a convenient drain, a trap placed inside the freezer, heat tape stopped short of the pan fitting, or a line routed where carts hit it. If a freezer has had the same drain problem more than once, ask the technician whether the routing itself should be redone. When a new freezer or a replacement evaporator goes in, the drain route, pitch, trap location and heat are worth checking before the box is loaded. The site's walk-in freezer installation guide covers what a proper install includes.

Preventing drain problems

Include the drain pan, drain line and drain-line heater in the six-month maintenance visit Heatcraft recommends. Keep shelving and carts away from the line where it leaves the box. In coolers, a periodic pan cleaning by a technician controls slime and odor. The site's walk-in cooler maintenance guide and the hub's preventive maintenance schedule list where drain checks fit.