Fixing the Ice Maker on my Kenmore Refrigerator

I have three full size refrigerators. I had two, but my mom's fridge died. The compressor failed. I can fix stuff, but wasn't going to put a new compressor in that old, small fridge. So I bought a nice used fridge that had an evaporator error code. Mom's kitchen cabinets were a few inches too low and this fridge wouldn't fit. She didn't want to tear out her cabinets so she got a small fridge and didn't need the one I got. I eventually fixed my fridge to get it out of my garage and put it in the kitchen to run it and test it out. Then people in my house went shopping and loaded it up. Apparently two fridges weren't enough for eight people.

Fast forward a couple years and error code SY EF (for the evaporator fan) showed up on the temperature display. If you search for 240389646.pdf, you'll find the wiring diagram for my fridge. It's a Kenmore, model 253.70313211, but everywhere online doesn't use the decimal point and just says it's model 25370313211.  

So when the evaporator fan failed on my Kenmore fridge, I had to unload the food into all the available space in the other fridges. I ordered a fan motor and figured this would be a great time to fix the ice maker. Or try.

The ice cube tray would never fill with water. I checked the valves and they all worked. I connected power to the ice maker water valve and water came out into the ice tray.

The motor that rotates the ice cube tray was fine. I took it out and connected a couple AA batteries to it and it ran the motor. The touch-arm (that detects if the tray is full) also was moving just fine. The switch on that arm tested fine. The ice-maker evaporator fan worked fine too.

The Source of the Problem?

The temperature sensor in the ice-cube tray is a negative temperature coefficient thermistor. I measured the resistance and it was around 5000 ohms at room temperature. After much searching, I found that it should have been closer to 11k ohms at room temperature. I found that information in the service manual in "February 2011 FGHB2844LFE 5995556437 Frigidaire Bottom Freezer Refrigerator Service Manual.pdf". It looks like Frigidaire made this fridge for Kenmore.

I put the ice cube tray in the freezer, which was around 0 degrees F and came back after an hour to read the resistance, and it was about 28k ohms. According to the chart, that means it was reading 32F. No wonder the computer never turned on the water. It thought the ice tray was too warm. 

Stupid Tax? Nope. Lazy Tax.

So I ordered the thermistor from Sears parts and paid way too much because I didn't feel like spending hours looking through the mouser.com catalog for the correct thermistor that really costs less than a dollar. Seriously, there are thousands of different kinds, 6048 of them. At least I didn't order it from Amazon where it was about $90. They must be making bank. There are other thermistors in that fridge that use the same resistance to temperature conversion. So I can deal with different style plugs - just cut and splice. 

 

First, I pulled out the shelves and the ice maker tray. 

Next, I removed the two screws holding the insulated front panel.

 This top panel comes out with a 1/4" socket or a long screwdriver bit holder.

I unplugged the wires and lifted up on the tab and the twist motor and ice cube tray then came out.

Next, there's this mounting bracket on the top. I pulled this toward me and it slid off the mounts. 

 

Next, I removed the three screws in the front holding the icemaker box in place. I didn't really need to pull the whole box out, but if I needed to service the evaporator fan, it needed to come out.

 Here's the thermistor kit I ordered.

Before I installed it, I verified the resistance at room temperature matched the temperature chart. I also used the foam to hold it against some frozen meat and the resistance converted to 17F. Then I used my infrared thermometer and it also said the meat was 17F. That was good enough for me, so I installed it.

I shouldn't have used any of the thermal mastic that came with it because it never dries. I hot-glued one side so it would stay put. Then I put some foam insulation tape on there to hold it in.

Here's what it looks like just before re-installing it.

 

 So I installed it and the temperature reading was wrong. I entered diagnostic mode on the fridge and the ice tray was reading 26F even though my IR thermometer showed 1F. 

I back-probed the terminals and measured the voltage across the thermistor and it was about 3V and a little tingly. More carefully, this time I measured AC voltage and didn't see any significant AC voltage on the multimeter, but still felt tingly on the door handle. I inadvertently discovered that there was a 117V AC difference between the thermistor and the fridge door handles while I was probing it with my volt meter.

Since I had replaced the plug, I thought maybe I swapped hot and neutral. Nope. The neutral wire was the ribbed side. Hot went to the black wire and that was confirmed on the wiring diagram. 

Now it makes ice once every few days or so. I still need to check the power connector on the main board to make sure it wasn't installed backwards from the factory. I'll update this post if and when I check that. 

For my future reference, a good substitute thermistor has parameters R = 10k ohms, B = 3320K, and they are only $1.72 each.