Refrigeration Adventures

I have a refrigerator from GE’s ZISS480 series. This particular one was made in 2003, but this family of side-by-side fridges made by GE in Louisville, Kentucky has been in production since the 1990s and is still made to this day with minor changes (which is great for parts availability), and sold under the Cafe, Profile, and Monogram brands.

I have the maintenance manual for this fridge and since it’s been in use for 20 years (we got it used), I’ve had to fix a few problems with it. Here I’ll describe the most difficult issue I’ve had to deal with - hopefully this will help you!

The problem started with the icemaker/water dispenser module. Appliance technicians recommend fridges without an icemaker or water dispenser, because most issues with the appliances seem to come from those. After this experience, I definitely agree. A separate ice maker machine that doesn’t involve your fridge seems like a more reliable solution.

Anyway, the ice dispenser chute has a flap door that opens to dispense ice, and closes when done. This area started icing over and weeping water. The icing then spread upwards into the icemaker compartment (as I learned later, this is not the kind of problem that can’t be ignored for long). First I changed the flap door, which did not help. After taking apart the freezer door, I realized that the flap door was not closing shut, which essentially meant the fridge always had a hole in it. The problem was in the dispenser solenoid responsible for closing the door - it had rusted through because water or condensate had been dripping on it. I replaced the solenoid, the door started closing again, and the chute stopped icing over. Yay! Problem solved! But it turned out not to be so simple.

The icing in the icemaker compartment persisted. A few months later, it grew to jam the icemaker, and a few weeks after that, the fridge stopped cooling properly. Temperatures in both compartments rose to unsafe levels and I started to stress out.

I followed the troubleshooting flowcharts in the manual, which led me to discover that the evaporator fan was blocked. On these refrigerators, the evaporator is in a compartment above the freezer, while the condenser is above the fresh food section. The evaporator fan is critical - both secitons of the fridge require forced airflow. The evaporator has ducts around it that guide the air through the coils, to the fan, and to the baffle that opens to send cold air to the fresh food section.

The evaporator fan would get blocked by icicles and stop spinning. At this point I went on a bit of a wild goose chase - the flowcharts were not helping. I reached the end of the flowcharts and had a technician check the sealed system to see if was low on refrigerant - but no, it was fine, and the tech had no idea what was wrong. He suspected that the fridge had a hole in it (which was not wrong - it had had a hole! I thought I’d fixed that problem…) Finally I decided to take apart the defrost system and see if it was working properly. I’d tried to get to it before, but the freezer ceiling panel under the evaporator and defroster was glued in place and would not budge.

The defrost system is essential to the operation of any modern fridge. Warm air enters the fridge when opening doors. As it’s cooled, the moisture condenses and must be taken care of - otherwise it will accumulate on the coldest surfaces, and eventually clog the whole fridge. So every few hours, refrigerators turn on a heater next to the evaporator coils. Frost melts and drips down from the evaporator, and is caught by a drain pan. Critically, the drain pan must keep the meltwater liquid and send it outside the fridge. This is typically done with a heated trough pan connected to a hose that runs to the outside of the fridge and then into another pan sitting under the compressor (using the heat of the compressor to speed up evaporation).

My first warning sign about the defrost system was that the pan under the compressor was bone dry. So the fridge was not able to get rid of defrost meltwater, and that’s what was dripping down into the freezer and jamming the evaporator pan. But I’d ran the defrost cycle manually multiple times, felt the heat from the defrost heater, and nothing improved. What was going on?

The process of taking apart the defrost system is shown in this video. I had to apply a lot of force to get the freezer ceiling panel to come down. It was being held by a combination of glue and a huge ice sheet enveloping the entire bottom of the compartment. The defrost cycle did nothing to melt it. There was a lot more water and ice up there than I expected!

The defrost drain pan sits on top of a big styrofoam block. This styrofoam was completely iced over too, and after blowing a hair dryer at it for a while, I tilted the defrost pan and unleashed a deluge of meltwater. It would have taken many days in the sun for this block of styrofoam-clad ice to melt. But when I turned on the defrost cycle again, both heaters (on the evaporator and under the bottom of the drain pan) got nice and hot.

So now I knew why the defroster was not working. The drain pan was completely encased in ice, and any time the heater turned on, most of the heat went to trying to melt the ice under the pan. The ice in the pan never melted, clogged the drain hole, and just kept growing into an iceberg. The defroster fell further and further behind, and meltwater eventually just flowed over the pan and down below. Even though the evaporator coils themselves were not getting iced over too badly, the ice underneath was really restricting the airflow - and blocking it completely, once it got in the way of the fan.

After making sure no ice or water was left anywhere around the evaporator, I removed much of the styrofoam (leaving only enough to support the drain pan in its original position) and put everything back together. After that, the fridge worked like new!

Root cause analysis

This experience made me understand the fundamentals of how refrigerators work better, and later I found other resources that explain what happened in more general terms. As an engineer, I like finding and fixing these kinds of issues - even though this was more stressful since my family’s food was on the line. In incident postmortems at work, engineers are trained to analyze incident timelines, response practices, contributing causes, and ultimately root causes to synthesize learnings. It’s fun to apply this practice to the fridge. What are some contributing causes that got the fridge to this point, and how could they be avoided?

  • The ice chute door solenoid was positioned where water or condensation was able to collect on it and rust it through. Sealing the solenoid compartment against moisture would have stopped this.
  • The evaporator fan is positioned in such a way that overflow from the defrost system can drip on it (and jam it when it turns to ice). Since the evaporator fan is essential to cooling, it would be better to reposition the fan or ensure overflow drips elsewhere (like through the suction side opening in the front of the ceiling panel).
  • The drain pan is engineered in such a way that water can get into the space between the pan and its styrofoam enclosure, or even into pores in the styrofoam enclosure. This means if the drain pan ever gets overwhelmed and overflows, an ice heatsink can form under the pan, disabling its heater and requiring the deep manual defrost that I ended up doing. It would be best to seal the space under the pan so no water can get in, making sure the space under the heater keeps acting as insulation (has low thermal conductivity) and all heat goes into melting the water next to the drain.

What about the root cause? As best I can tell, it’s that last one - an evaporation system drain pan that is too easily overwhelmed by an excess of meltwater. But there’s room for ambiguity here, which is why attributing the root cause is not usually the point of incident post-mortem exercises - the focus is on learning how to operate the overall system safely and reliably.