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Viking Refrigerator VCBB360RSS Defrost Problem

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Posted: Sat Aug 7th, 2010 11:12 pm

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hafez
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My defrost circuit appears to have a problem as I get frost build up in the freezer, but I can’t figure out the problem. I’ve tested the heating element and the defrost terminator and they’re both OK. When the freezer is cold, I get a full 120V on the E5 probe point on the High Voltage board. But the defrost heater relay never seems to close and so there’s no voltage on E6. Even when I force defrost using the keypad (Display Off+Max Ref), the defrost heater relay doesn’t close, and I do not see the low voltage signal from the control board that’s supposed to close the relay on R9 as the manual suggests. I’ve tried replacing the low voltage control board but it didn’t change the behavior. It seems everything is working fine, except the defrost heater relay never gets the signal it needs to close and complete the heater circuit. But I have no idea why this signal is not coming from the low voltage control board. It controls everything else just fine and sends the signals to turn the compressor/evaporator fan relays on/off upon forcing them (or during normal operation). Just not the defrost heater relay. I’ve looked everywhere for an answer, but nothing. Any and all help would be appreciated.

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Posted: Sun Aug 8th, 2010 07:57 am

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Scottthewolf

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Looks like you need to replace the high voltage control board. Since both the defrost heater and the defrost thermostat are both 120 volts AC, those both are controlled by the high voltage board.

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Posted: Sun Aug 8th, 2010 09:13 pm

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hafez
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Scott, many thanks for the response. It’s true that the 120V AC voltage for the defrost heater and thermostat comes from the high voltage board through a relay (labeled “def D1” on the diagram). But this relay is controlled by the low voltage control board which sends a low voltage DC signal to close the relay, thus completing the AC circuit to the heater. That’s why I suspected the low voltage control board at first and tried replacing it. Am I missing something? Are you suggesting that something on the high voltage board prevents this low voltage signal from the control board to be generated or maybe that the relay itself is bad?

Anyway, I will try replacing the high voltage board as you’ve suggested and report results. Thanks again.

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Posted: Mon Aug 9th, 2010 01:57 pm

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Samurai Appliance Repair Man
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Sounds like you have access to the voltage and schematic information. Did you check for voltage to the relay coils before you replaced the low voltage board? Do you have a schematic or tech sheet you can post or fax? My fax number: 866-315-4504

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Posted: Mon Aug 9th, 2010 04:39 pm

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RegUS_PatOff
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hafez,

Is the Service Manual you have ?

m1630115

SERVICE NOTEBOOK

REFRIGERATOR

VCBB360R / VCBB362R (Right) – VCBB360L / VCBB362L (Left)

if you could post your email address I have some service bulletins

Samurai, links PM'd

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Posted: Mon Aug 9th, 2010 06:27 pm

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hafez
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Yes. I do not believe the low voltage control board raises the voltage to the relay coil as it is supposed to (neither the old board or the new board). The manual says that it should be approximately -25V DC when relay is open and -11V DC when closed. What I measured is roughly -26 to -29V DC even when I initiate force defrost. I also measured the voltage to the compressor/evaporator fan relay coils and they are roughly -29V DC when the fans are off, but they increase to -22V DC when the fans are on which appears to be the correct behavior (although slightly lower voltages than the manual says). I'm attaching the link to the service manual here.

http://rakerprivatelibrary.com/Refrigerators_Freezers/Viking/Viking%20Ref%20VCBB360%20-%20362.pdf

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Posted: Mon Aug 9th, 2010 06:30 pm

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hafez
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My email address is .... @yahoo.com Appreciate all the help.

Last edited on Mon Aug 9th, 2010 07:50 pm by RegUS_PatOff

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Posted: Mon Aug 9th, 2010 07:52 pm

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RegUS_PatOff
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same service manual I have ..

Service Bulletins link emailed ..

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Posted: Tue Aug 10th, 2010 01:39 am

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KurtiusInterupptus

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here's a thought; does you unit have a "showroom switch" on the top right of the control box? if so, this could be your problem. on older models ,the heaters are wired through this switch (another fine piece of viking logic) and they instruct us to bypass this switch anytime we work on one that has it,problem or not. to bypass...

1)cut the connectors off the white and blue wires and wire nut them together

2)cut and cap the black wire

hope this helps you...if it does, you would be the first person i have personally heard of that had this problem ,confirmed.

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Posted: Tue Aug 10th, 2010 02:40 am

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hafez
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Thanks KurtiusInterupptus. I don't think the Showroom switch is the problem in this case because when I bypass the defrost relay by splicing together the wires going to E5 and E6, the heater circuit works just fine. It just seems the realy coil never gets powered for some reason. But I'll give your bypass idea a shot and let you know if it makes a difference.

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Posted: Mon Oct 11th, 2010 07:12 pm

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hafez
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Just want to close thie loop on this. I finally ordered and replaced The HIGH VOLTAGE BOARD and that was the problem. Replacing it resolved the defrost issue. Works good as new now. Thanks to all who posted suggestions, particularly Scottthewolf.

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