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FIXED Subzero refrigerator/freezers 700TCI- Ice buildup


Premium Member
Jun 26, 2022
Monterey, CA
Model Number
700 TCI
More than 10 years
Hi, my refrigerator seems to be having similar problems as discussed in
although my 700 TCI is a few years older and it has a single compressor with the evaporator located
underneath the bottom freezer drawer. I started noticing grinding sound a few months ago and initially thought
it was the compressor dying but when I opened the kick plate to see and touch the compressor I realized the
compressor was working fine (though hot to the touch) and the sound came from the back of the refrigerator.
So I thought it must be the fan hitting the ice buildup around it. I contacted a local technician who spent only
a few minutes on it and concluded that it was the defrost terminator that's gone bad. So he ordered a replacement
and put it in a few days later. The refrigerator was turned off while waiting for the replacement part so naturally
all the ice had melted and there was no more grinding sound after the new defrost terminator was put in.
So we thought the problem was fixed. But a few weeks later the sound came back and I saw the ice buildup
again. This time he suggested I contact Subzero.

I followed the thread above carefully and did some checking on my own. Here is what I noticed:
1) The refrigerator works fine as far as being able to maintain the set temperatures (38 for the frigg
and 4 for the freezer), 2) the ice around the evaporator builds up slowly over many days, 3) the
defrost rod seems to be working. When I shut off the unit and turn it back on, the defrost rod is
extremely hot and I could see the ice around it melting. 4) I'm not 100% sure about this but I believe
the compressor never shuts down ever since this problem developed. The compressor is always hot
to the touch and I can feel the slight vibration when I place my hand on it. Since the compressor is always
on, the condenser fan is always on which is very noticeable. The only time the fan is off is when I open
the refrigerator door. 5) I am wondering if the excessive running of the compressor is causing the temperature
to run well below the set freezer temperature which then causes more ice to form on the evaporator than
can be removed by defrost cycles. This is a pure conjecture and I could be dead wrong. But I did placed
a thermometer in the bottom freezer drawer and saw a reading of -14 degree while the refrigerator reading
showed the set temperature of 4 degree, Why the discrepancy?.I have no idea.

Reading through the previous threads on Subzero I have no doubt there are members on this forum
who are far more knowledgeable than I about troubleshooting these problems. I really appreciate
your time and expertise and look forward to hearing from you.



IMG_1682.jpg IMG_1683.jpg IMG_1684.jpg

Is that white spot in the center frost or glare from the pic? Freezer display goes no lower than -5. Compressor should shut off during defrost, you forced a manual defrost by turning unit off & then on. Comp run is controlled by the upper drawer thermistor located the reed switch. Opening the door has nothing to do with the condenser fan, did you mean evap fan.
The white spot was real frost and not photo glare. I've attached a photo I took just now from a slightly tilted angle. The refrigerator has been running for 6 days after a complete shutdown to allow the ice to melt. I know the display doesn't go lower than -5. I set it at 4 and the display always shows 4. I just put a thermometer at the bottom drawer again and waited about 20 minutees. It shows -13 degree. See attached photo.

IMG_1695.jpg IMG_1696.jpg

It's possible it gave a wrong reading but I was just wondering if there is an outside possiblity that the motherboard is bad which causes the compressor to run non-stop which causes the temperature to dip well below 4 degree which caurses the ice buildup. Finally, about the fan noise. It's possible the evap fan was running but the condenser fan was defintely also running since it sits not far to the right of the compressor behind the kicker plate so it's very easy to notice.

Thanks, Paul.
That looks more to me like a drain issue. Check drain heater 1900 ohms. Take a pic of top left of evap where heat exchanger comes in.
Is this what you're looking for? I don't know where the drain heater is located. Can I access it without shutting down the unit?

Yeah, just wanted to see if the permagum was all there. That's alot of frost but I guess it's because you have the drawer out. I would shut it down. slide out the bottom tray, locate the connector to the defrost drain heater (silver braided) behind or near the water valve, give it a liitle tug to see if it's frozen in the drain, turn unit back on and check for 120V to heater and if OK check ohms of heater. If you're leery about pulling that bottom out I would call SZ for them to come out. When I pull this out I slide a piece of plywood under to keep level because it will drop down and is a PIA to get back up. If you do pull it out look at the drain pan, it's probably dry.
I can see the drain heater in the schematics now. So the two end points around the drain heater should be 120V when unit is on and 1900 ohms when removed from power and it's located in the bottom tray? I think I can do that. Will heep you posted. Is drain heater always on or only during defrost cycles? Thanks again.

So the heavily iced part is where the openning to the drain hose is and it's frozen solid. That's why you suspected it's the
drain issue? Is the drain pan part of the bottom tray or it sits below it? I wonder if I can stick a tiny camera behind the
compressor to see if the drain pan is dry or not. This way I can give you the answer without having to shut down the unit
or slide the bottom tray out.
Not sure if this is the drain pan or not but I pointed the camera towards the bottom of the compressor tray and
it is dry as you speculated.

Hard to tell from that, it's in the rear of that slide out tray. It won't have water until defrost cycle.
Hi Paul, I was away for a few days when I came back last night I noticed the refrigerator temp is 52 degree (setting 37) while freezer is normal at 4 (setting 4). The ice buildup on the evap didn't get bigger. Could the air circulation to the upper chamber somehow be blocked? I will continue with the troubleshooting today. Thanks.
I shut down the unit for one minute and turned it back on to force a defrost cycle. I do see water coming out of a PVC pipe with
two metel'ish strings going into it which I assume is the heater. I took a picture as close to the PVC opening as I could. The water comes out in slow drips though.

Are you running it with the drawer out? That's a wacky frost pattern. What's the bottom 1/2 of the evap look like.
No, drawer is always in with some food in it. The evap cover however was not in. I removed it last time when I checked the evap and haven't put it back. Could that be the problem?
Is that fan behind the evap running? Cover has to be on, that ice on the bottom doesn't belong there, was it all gone after the defrost

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