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FIXED Subzero refrigerator/freezers 700TCI- Defrost Problem

drobins9

Premium Member
Joined
Oct 10, 2021
Messages
6
Location
Chevy Chase, MD
Model Number
700TCI
Brand
Sub Zero
Age
6-10 years
Hello- I have side-by-side Subzero 700TCI refrigerator/freezers. One of them iced up about 6 months ago, and water was gathering on the bottom of the refrigerator. EC codes 40 and 24 were set. After researching, I concluded the refrigerator drain was clogged. I unclogged it, defrosted the freezer, and it seemed to work fine. Over time, the freezer started getting a little warmer. In the last week, the evaporator fan got noisy (hitting ice), and EC 40 and 24 tripped again.

I took it apart, and the evaporator was frozen up. There was also ice on the back wall. There was not ice on the sides or the front. From everything I am reading, that seems to be a defrost problem.

I turned the freezer on (with the drawers removed) and held the ice button, which I understand triggers a manual defrost. The v-shaped defroster heating element under the condenser heated up in what seemed to be the 100-140 degree range (a little hard to tell with my infrared thermometer...) As water melted and dripped onto the V-shaped heating element, it would make a small sizzling noise. I believe there is a separate defroster heating element that snakes back and forth across the coil, and that one did not heat up at all.

A picture is attached.

I would greatly appreciate any help on how to diagnose what part is bad (from my reading, I'm thinking it is likely either a thermosistor and/or heating coil) and would also appreciate any guidance on replacing.

Thank you!
Don

Subzero.jpg
 

paulhl

Premium Member
Joined
Jul 3, 2021
Messages
90
Location
Flemington NJ
Two separate defrost heaters. The lower one is the trough heater, the one in the evap is the main. Must check terminator behind fan assy since it only supplies power to upper heater and also check heater if terminator is good. Have replaced several heaters and many terminators.
 

rickgburton

Appliance Tech - Moderator
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Messages
44,256
Location
Murray, Utah 84107, United States
The problem is most likely the control board. There's only one defrost heater and like a light bulb, it's either good or bad. Since it turned on the defrost thermostat and heater are good. The only thing left is the control board. The electronic control regulates defrost intervals with what is called "Adaptive Defrost." With adaptive defrost, the length of time that the heater actually stays on to defrost the evaporator and satisfy the defrost terminator is sensed by the evaporator thermistor. The length of heater ON time determines the number of hours before the next defrost. For instance, if the heater stays on for a shorter time than normal, the electronic control increases the time between the next defrost. If the heater stays on for a longer time than normal, the electronic control decreases the time between the next defrost. This is an ongoing process whereby the defrost time and the defrost interval will vary by unit use.
To initiate a manual defrost, turn OFF master power switch for 10 seconds then turn back ON. The control will initiate defrost upon power up, provided the evaporator temperature is below 20°F. If the evaporator is warmer than 20°F, the evaporator thermistor must be disconnected before initiating defrost.
 

paulhl

Premium Member
Joined
Jul 3, 2021
Messages
90
Location
Flemington NJ
Your whole explanation is for the older 700's with one comp & one evap. From his pic he has a newer one with two comp, two evaps and the two heaters are separate.. Bad terminator or heater, hopefully the term cause the heater is a pia to replace.
 

rickgburton

Appliance Tech - Moderator
Staff member
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Jul 11, 2006
Messages
44,256
Location
Murray, Utah 84107, United States
From his pic he has a ..........
I don't go by pics, only model numbers and for the 700TCI my explanation is spot on. I'm never wrong. LOL
 

paulhl

Premium Member
Joined
Jul 3, 2021
Messages
90
Location
Flemington NJ
His is obviously a -2 unit so don't LOL, spot on for an older 700TCI with one comp and one evap below the freezer drawer but not for his.
 

drobins9

Premium Member
Joined
Oct 10, 2021
Messages
6
Location
Chevy Chase, MD
Thank you both for your help.

Definitely correct 2 separate elements Paul, as the bottom one (trough defroster you called it) gets hot, and the one on the evaporator doesn't.

I took off the evaporator thermistor, and there is no continuity on it by default or at any temperature. So obviously it's bad. I thought I had read disconnecting the thermistor would allow the defroster to turn on. The evaporator one does not turn on when I kick on the manual defrost cycle while the thermistor is disconnected. But looking at the manual, only the bottom one should have infinite resistance if cold, so maybe the evaporator one is not to turn on without a good thermistor.

There is a black and brown cable that hooks up to the evaporator defroster. The manual seems to only talk about the expected resistance on what it calls the "defrost heater," but since it refers to the "defrost terminator" separately from the "evaporator thermistor," I'm not sure the spec it shows (20-30 ohms) is the right spec. But I hooked the multimeter up to that, and it also has infinite resistance. I guess that is a bad sign?

Just to be sure there wasn't a connection problem (my multimeter terminals are a little small), I wedged copper wire in both slots of both plugs but that didn't help; still infinite resistance.

Does that mean it is likely both the thermistor and the evaporator defroster are bad? If so, any tips on replacing the defroster, It just plugs in, but there are 4 wire brackets holding it on to the evaporator that look not-so-fun.
 

paulhl

Premium Member
Joined
Jul 3, 2021
Messages
90
Location
Flemington NJ
Forget about the thermistor, if your evap is frosted like that pic the terminator should have continuity. If not you can unplug it. short the connector and see if heater gets hot. Terminator on top of evap on r/s
 

rickgburton

Appliance Tech - Moderator
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Jul 11, 2006
Messages
44,256
Location
Murray, Utah 84107, United States
The defrost terminator (thermostat) must be below about 40°F to show continuity. Find the two ends of the defrost heater and check it for continuity.
 

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
44,256
Location
Murray, Utah 84107, United States
Paul, I get the feeling you don't like it when you're wrong. But dude, when you're wrong you're wrong.

His is obviously a -2 unit so don't LOL, spot on for an older 700TCI with one comp and one evap below the freezer drawer but not for his.
Let's take your last post and break it down.
His is obviously
What makes it obvious?
spot on for an older 700TCI
Older, newer, middle age, it's spot on for Model #700TCI and that's what his model is. You're not going to tell me Sub Zero made a new model, Kept using an old model number and now use newer and older??
but not for his.
He said his model number is 700TCI and you said I was spot on for that model so instead of arguing with me just read what I write.
so don't LOL
0df9d6dd.x120.gif
OK
 

drobins9

Premium Member
Joined
Oct 10, 2021
Messages
6
Location
Chevy Chase, MD
So I had put the terminator in ice water when it showed no continuity. I tried sticking it in the freezer twice. Both times, it comes out of the freezer with full continuity. At some point as it warms up, there is an audible click, and the continuity is gone. I think that means it's good?

I tried shorting out the connector in the refrigerator that the terminator plugs in to, held the ice button for 5 seconds, and still the bottom defroster heated, but the top one on the condenser did not.

Assuming the defrost heater doesn't have to be cold, I had hooked up the multi-meter to the connector of the defrost heater (one wire travels to each end) and there was no continuity at all.

I guess it sounds like the actual defroster is the more-likely culprit?

Are there any tricks to removing and replacing the clamps that hold it on? I just don't want to damage the evaporator in the process.

Don
 

rickgburton

Appliance Tech - Moderator
Staff member
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Jul 11, 2006
Messages
44,256
Location
Murray, Utah 84107, United States
I think that means it's good?
Correct.
held the ice button for 5 seconds
Why? You must have missed this:
To initiate a manual defrost, turn OFF master power switch for 10 seconds then turn back ON. The control will initiate defrost upon power up, provided the evaporator temperature is below 20°F.

the actual defroster is the more-likely culprit?
Correct. The defrost heater is the problem. Part #4201970. I'll see if I can find a part link for you. So far it comes up as unavailable:
 

drobins9

Premium Member
Joined
Oct 10, 2021
Messages
6
Location
Chevy Chase, MD
Thanks for all your help. Held the ice button because I had removed the drawers and completely defrosted the freezer (used a heat gun to expedite it and plugged the drain and used a shop vac to try to keep the drip pan (which was bone dry before I started) from overflowing, so the freezer compartment was room temperature.

Don
 

paulhl

Premium Member
Joined
Jul 3, 2021
Messages
90
Location
Flemington NJ
Rick, FYI there is a 700-2 & a 700-3. That's the wrong def. heater but I'm done arguing. All SZ parts go by ser# and holding the ice button for 10 sec is the way to put it in defrost above ser# 181xxx

BTW Don you can just shut down the freezer & let the ref. run. With the unit off hold in the frz temp warmer button then turn on unit. You should see two dashes for frz temp
 
Last edited:

rickgburton

Appliance Tech - Moderator
Staff member
Joined
Jul 11, 2006
Messages
44,256
Location
Murray, Utah 84107, United States

drobins9

Premium Member
Joined
Oct 10, 2021
Messages
6
Location
Chevy Chase, MD
Hi, Paul- Per our separate message discussion, you asked me to pose this question here so you could reply for the benefit of anyone else who might need this:

I received the defrost element yesterday, part number 7041264. I am planning to install it over the next week or so. The wiring harness will simply plug in, but I see that the heater is attached to the evaporator by 4 metal clips. The clips do not appear "springy." There does seem to be a part protruding from the clips that I could lock on to with needlenose pliers and force open, but (1) I would have to re-close it with the new heater, and (2) I want to be careful not to put too much force on or damage the evaporator tubing to which the heater is clamped.

Could you provide any tips/advice on the removal of the old defrost element and installation of the new one?

Thank you!
Don
 

paulhl

Premium Member
Joined
Jul 3, 2021
Messages
90
Location
Flemington NJ
I use a piece of thin(1/2") wood as a brace under the clip, then pry up under that tab. At that point a pair of vice grips to pull it off. Take notice of the route the leads take. You have to remove the screws on the r/s and loosen those on the left to tilt the evap out enough to get the heater behind the end of the evap. Put a paper towel over the drain hole, the screws are stainless and tend to drop off screw driver.
 
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