stc-1000 relay.

[pucstpn86]

I recently built an stc temperature controller. The heat side works fine, but the cold side never shuts off. Even if I turn the power off to the unit the cold side is still powered. Had anyone ever come across this?

Thanks

 

[day_trippr]

If you wired the hot and cold relays to a duplex wall outlet, did you remember to break the hot-side bridge between the two?

When you write "turn the power off to the unit", what is "the unit"?

Cheers!

 

[pucstpn86]

Yeah I wired it to a duplex outlet and broke the tab on the hot side. The unit would be the actual stc-1000 when I turn the power off the cold outlet still has power

 

[day_trippr]

I think you're going to need to post a picture or a drawing of your wiring, because obviously you have a sneak path to AC somewhere...

Cheers!

 

[GotPushrods]

Unplug everything and remove the 2 wires from the cooling relay. Is there continuity between the two sides of the cold relay? What is the resistance?

 

[pucstpn86]

Here's the diagram I used. I also took all the connections off except the cold relay and the outlet still had power. I'm assuming the relay is stuck.

I'll have to check continuity when I get home tonight. If the relay is stuck on is there a way to reset it some how?

 

[day_trippr]

So you're saying if you remove the plug in the diagram from the wall outlet, there's still power going to the fridge?
That's clearly unpossible if you followed that diagram.

Otoh, if by "turn the power off to the unit" you mean you programmed the controller to shut off the relay but it never actually shuts off, then, yeah, your controller is broken. Might be the relay, but it might be the circuit that controls the relay coil...

Cheers!

 

[pucstpn86]

So basically the only connections are a hot lead going into the stc on the left side of the cold relay, then it from the right to the hot side of the outlet, then a cold lead to the other side of the outlet and a ground connection. And the outlet is constantly powered no matter what I do with the stc unit itself. I ordered a replacement, I'll update tonight after I try to swap it out

 

[raouliii]

It sounds like the cold relay is stuck closed and may be the result of drawing too much current at switching. What are you powering with this setup?

 

[pucstpn86]

Yup bad unit, New unit worked perfectly wired the exact same way.

 

[raouliii]

If the old unit failed because of the external load, it will likely happen again.

 

[vtfan99]

If the old unit failed because of the external load, it will likely happen again.

Resurrecting an old thread here, but I appear to have the same problem. The controller cools to the set point but the cool relay never shuts off. If you are saying the external load may have caused this, what do I need to change to avoid it overloading a new unit? It is powering a 7 cubic chest freezer and that is all. My unit is wired exactly as the picture above. Do I need a different controller? Could a power surge during a storm cause this? If so, how would I change the wiring to protect against that in the future?

Thanks!

 

[IslandLizard]

Resurrecting an old thread here, but I appear to have the same problem. The controller cools to the set point but the cool relay never shuts off. If you are saying the external load may have caused this, what do I need to change to avoid it overloading a new unit? It is powering a 7 cubic chest freezer and that is all. My unit is wired exactly as the picture above. Do I need a different controller? Could a power surge during a storm cause this? If so, how would I change the wiring to protect against that in the future?

Thanks!

A 7 cu ft chest freezer shouldn't pull more than a couple amps, except for a brief moment during startup.

Does the relay not shut off or are the contacts fused together? The latter could happen with an overload at some point or just a fluke relay. If you're handy with electronics you can replace the relay. A power surge can damage the electronics in the controller, but it would typically not work at all after that.

 

[vtfan99]

A 7 cu ft chest freezer shouldn't pull more than a couple amps, except for a brief moment during startup.

Does the relay not shut off or are the contacts fused together? The latter could happen with an overload at some point or just a fluke relay. If you're handy with electronics you can replace the relay. A power surge can damage the electronics in the controller, but it would typically not work at all after that.

I will need to go pull some things apart and take a closer look to see if anything is fused together. Simple observation shows that the controller shuts off the cooling mode (no red dot next to cooling) but the cold side of the outlet still has power. Then, because the keezer is still cooling, the controller eventually kicks on the heating side (red dot next to heat) yet the cold side of the outlet still has power. The first time this happened was during a recent snowstorm, so that's what has me thinking power surge. It also resulted in 4 frozen kegs.

I suppose I will start by trying to replace the duplex outlet so I don't have to rip apart the inside of my keezer.

 

[IslandLizard]

I will need to go pull some things apart and take a closer look to see if anything is fused together. Simple observation shows that the controller shuts off the cooling mode (no red dot next to cooling) but the cold side of the outlet still has power. Then, because the keezer is still cooling, the controller eventually kicks on the heating side (red dot next to heat) yet the cold side of the outlet still has power. The first time this happened was during a recent snowstorm, so that's what has me thinking power surge. It also resulted in 4 frozen kegs.

I suppose I will start by trying to replace the duplex outlet so I don't have to rip apart the inside of my keezer.

Sounds like the cold relay's contacts are fused.

If you have a multi meter you can test for permanent continuity of the cold relay. It would always be ON if the contacts are fused, even if the STC is not powered. I'd check that first, after unplugging the unit from the mains.

How would a duplex outlet fail, apart from hitting it with a hammer? Besides, the STC powers it. Should we assume the STC/freezer worked fine before, and it's not bad wiring?

 

[vtfan99]

Sounds like the cold relay's contacts are fused.

If you have a multi meter you can test for permanent continuity of the cold relay. It would always be ON if the contacts are fused, even if the STC is not powered. I'd check that first, after unplugging the unit from the mains.

How would a duplex outlet fail, apart from hitting it with a hammer? Besides, the STC powers it. Should we assume the STC/freezer worked fine before, and it's not bad wiring?

Yes, the STC/freezer worked fine for about 9 months...flawlessly actually. I believe I have a multi meter around the garage someplace. I will see if I can test the relay. Thanks for your help :rockin:

 

[vtfan99]

Sounds like the cold relay's contacts are fused.

If you have a multi meter you can test for permanent continuity of the cold relay. It would always be ON if the contacts are fused, even if the STC is not powered. I'd check that first, after unplugging the unit from the mains.

How would a duplex outlet fail, apart from hitting it with a hammer? Besides, the STC powers it. Should we assume the STC/freezer worked fine before, and it's not bad wiring?

So, I readily admit that I have difficulty wrapping my head around most things related to electricity. I have used the multi-meter I have, which is pretty old and rarely used (there is no audible tone to indicate continuity). From what I can tell the cold relay does not appear to be fused. I tested the probe connectors on the unit and my meter reading changed, so I assume that indicates continuity. That did no happen when testing either the cold or hot relay.

So, either I'm more clueless than I thought and I'm using my multi-meter incorrectly, or there is something else wrong. Is there something within the controller that could cause the unit to turn on both relays when in heating mode?

I've bought a new unit and am close to just re-wiring everything. Just seems easier than me bumbling around like a moron.

 

[vtfan99]

I don't know if it matters or not but I don't have an STC...I have an inkbird...but they are essentially the same thing.

 

[jleiii]

So, I readily admit that I have difficulty wrapping my head around most things related to electricity. I have used the multi-meter I have, which is pretty old and rarely used (there is no audible tone to indicate continuity). From what I can tell the cold relay does not appear to be fused. I tested the probe connectors on the unit and my meter reading changed, so I assume that indicates continuity. That did no happen when testing either the cold or hot relay.

So, either I'm more clueless than I thought and I'm using my multi-meter incorrectly, or there is something else wrong. Is there something within the controller that could cause the unit to turn on both relays when in heating mode?

I've bought a new unit and am close to just re-wiring everything. Just seems easier than me bumbling around like a moron.

Disconnect the power to the STC and the Freezer, remove both wires from the cooling relay and cover with tape or wire nuts. Set your meter to OHMS/Resistance lowest scale, connect the probes to the 2 cooling terminals. If you get a zero reading (or anything close to zero), then the relay or board has a short.
If you do NOT get a zero reading, leave the probes connected to the cooling terminals and power on only the STC. If you get an immediate click, and a Zero reading the circuit driving the relay has failed. If you do not get a immediate click, but it does click once it goes into cooling mode, you shoud then see Zero on the meter. This suggests a wiring problem to the freezer.
Did you disable the freezer thermostat?

 

[IslandLizard]

So, I readily admit that I have difficulty wrapping my head around most things related to electricity. I have used the multi-meter I have, which is pretty old and rarely used (there is no audible tone to indicate continuity). From what I can tell the cold relay does not appear to be fused. I tested the probe connectors on the unit and my meter reading changed, so I assume that indicates continuity. That did no happen when testing either the cold or hot relay.

So, either I'm more clueless than I thought and I'm using my multi-meter incorrectly, or there is something else wrong. Is there something within the controller that could cause the unit to turn on both relays when in heating mode?

I've bought a new unit and am close to just re-wiring everything. Just seems easier than me bumbling around like a moron.

Maybe it's toast, as soon as you plug it in, the cold relay closes regardless of settings and temps. Or a faulty sensor. Troubleshooting is never easy. Even worse when it's intermittent.

 

[vtfan99]

It gets even worse. After testing it and plugging it back in (a few times)....it works fine now. Turns off when its supposed to and turns on when it's supposed to. Not very comforting but I'll keep watching to see if it flakes out again.

Thanks for your help IslandLizard.