Bad hot wire relay on GE ZDP36 Monogram range

[joeswamp]

The hot wire relay on my GE Monogram oven has given up the ghost, and it looks like it's NLA. There's some crazy guy on ebay selling replacements for like $600, but what I'm wondering is what's so special about these things?

These relays don't use electromagnetic coils, but instead use some kind of bimetallic strip to close the contacts. I think they were traditionally used on ovens and big motors, but not sure if they're used now. Is the thermal action some kind of safety feature or was it done for cost purposes?

Can I replace it with a $30 high amperage contactor on DigiKey? Or do they draw too much coil current? Is there a standard replacement for GE P/N WB21X5362? This same relay was used on Thermadors and Jennairs as well.

[rikishi]

Not cheap, but perhaps consider https://www.searspartsdirect.com/product/668mqeqj36-0022-364/id-wb21x5362 .

Unfortunately, an electromagnetic replacement by itself won't work -- the hot wire is likely in series with some other element (rather than being operated on line voltage) and the thermal delay may also be important.  Do you have a schematic that shows how the components are interconnected?

 

[joeswamp]

Actually that is pretty cheap, too good to be true. I might give them a call but this thing hasn't been made in years. I'm pretty sure Sears doesn't have enough people left to keep the website updated.

I did figure out why hot wire relays were used. Not only is the hot wire relay completely silent, but the slow reaction time of the bimetallic strip filters the switching action of the thermostat, resulting in much less relay cycling. A couple folks have tried replacing these relays with normal contactors and it works fine, but all the frantic clicking makes the oven sound like a machine gun.

You can buy a solid state relay that will work, but I'm a little nervous with those because they tend to catch fire when they overheat. I think I'm going to try burnishing the relay contacts on mine and see how long it lasts... A replacement is still cheaper than a new oven.

[rikishi]

I don't know the details, but if you have a wiring diagram and determine that line voltage is applied to the input to cause the contacts to close, you could bench test it to see whether the heater gets hot, the bimetallic strip operates mechanically, and contact is established.  From those results, you could make an appropriate repair (such as cleaning the contacts) and retest.  If it's hopeless, then maybe the Sears part (if it really exists) is a good deal.  Otherwise, you could build an electronic equivalent.  Solid state relays in this current range are designed to mount on a heat sink.  The element current and on-state voltage drop are known, so you can calculate power dissipation.  Knowing the thermal resistance of the heat sink, you can determine the temperature rise and confirm that the device is operating safely within its ratings.

Another option is to obtain a currently manufactured thermal relay (designed for different equipment), but with adequate voltage and current ratings and compatible input, and adapt it to fit into and connect properly to your range.

[Budget Appliance Repair]

@joeswamp If you order the one from Sears you can get 10% off which would pretty much cover the shipping charge if you use the code PARTS in the discount code box when you order.

I would advise you not to waste your time calling Sears to see if it is really available - It says "In Stock" and that is what any phone rep will see and tell you rather they really have it or not.    If you think you might want the new one I would just order it and still try to fix yours in the mean time because you won't know until at least a week, (possibly a week and half), before they get back to you with a canceled order because the part is no longer available, (that's just the crappy service you get from Sears - and typical).  

The price itself isn't to good to be true - if by some chance they do have one you will get it for the listed price, (sometimes you find some really good prices on items from Sears, maybe price was never updated because it's not a common part).

A multi-company parts lookup site that checks about 19 different popular part houses all show no longer available and went NLA in Dec.2014 - You might get lucky and Sears really does still have one in stock but I thinks the odds are kind of slim.

[Budget Appliance Repair]

Here are a few options if the Sears one isn't available - these are a little better then the crazy $500 - $650 ones on Ebay.

These are all parts that are perfect substitutes with the exact same wiring and specs.

$200+$9.35 Ship - https://www.ebay.com/itm/Thermador-Hot-Wire-Relay-414589-14-19-129-WB21X5362-210768-SPRING-SPECIAL/273923794352

$250+$9.35 Ship - https://www.ebay.com/itm/Frigidaire-Hot-Wire-Relay-5300632171-00632171-0632171-632171-fits-others/283648590597?epid=5017975034

$350+Free ship - https://www.ebay.com/itm/NEW-Frigidaire-Hot-Wire-Relay-5300632171-00632171-0632171-632171-SHIPS-TODAY/223493687082

$389+Free ship - https://www.ebay.com/itm/U5300632171-Frigidaire-RELAY-Hot-Wire/283572291982

 

[joeswamp]

Thanks for all the help everyone. I took the relay out, took it apart and cleaned the contacts -- the one set controlling the baking element was pretty burnt. I took a strip of aluminum and wrapped it with a folded piece of automotive sandpaper (lubricated with wd40) and worked my way up from 320 to 1000 grit. I then cleaned the contacts with alcohol. The contacts aren't perfect but they're a whole lot better than they were, and the oven works fine now.

Actuating the relay with the cover off was pretty interesting. My schematic showed the heating coil at 120V, so I just plugged it into the wall. The heating wire is super fine -- like much finer than a human hair, and the relay takes 10-20 seconds to actuate. What a crazy gizmo this is. Nowadays we'd use a simple microcontroller with a filter on the relay signal, but this thing implements the same thing mechanically.

Thanks again for the help. Not sure how long these contacts will last, will probably start looking for a replacement (and will see if Sears actually has them).

[Boedacious]

On 5/16/2020 at 4:00 PM, joeswamp said:

Thanks for all the help everyone. I took the relay out, took it apart and cleaned the contacts -- the one set controlling the baking element was pretty burnt. I took a strip of aluminum and wrapped it with a folded piece of automotive sandpaper (lubricated with wd40) and worked my way up from 320 to 1000 grit. I then cleaned the contacts with alcohol. The contacts aren't perfect but they're a whole lot better than they were, and the oven works fine now.

Actuating the relay with the cover off was pretty interesting. My schematic showed the heating coil at 120V, so I just plugged it into the wall. The heating wire is super fine -- like much finer than a human hair, and the relay takes 10-20 seconds to actuate. What a crazy gizmo this is. Nowadays we'd use a simple microcontroller with a filter on the relay signal, but this thing implements the same thing mechanically.

Thanks again for the help. Not sure how long these contacts will last, will probably start looking for a replacement (and will see if Sears actually has them).

Thanks Joe, this fixed my oven!

 

[BigFred]

Hi guys,

I had a GE repairman here just before Christmas.  He said that my relay was shot and gave me the item number as GE didn’t stock it any longer.  
 

I did buy one from eBay and it arrived today.  Took the bottom panel off and I’ll be damned if I can find where it goes.  Nothing on the board looks anything remotely like this. 

What am I missing?  

Thanks in advance!  
 

 

[Terry Carmen]

On 5/16/2020 at 6:35 AM, Budget Appliance Repair said:

You might get lucky and Sears really does still have one in stock but I thinks the odds are kind of slim.

If they have the part, I'd buy a few, sell them on ebay and buy a new stove. 8-)