Coolbot and LG Window Unit

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Mike Howard

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Not sure where to actually put this information, but since I was unsuccessful at locating any troubleshooting repair topics anywhere on the net, I am posting this here in case anyone else has the same issue and goes looking for details.

I have a 5 x 8 Walk In Cooler with a Coolbot Pro and an LG1216ER 12,000 BTU Window Air Conditioner. I've had this unit for about 6 months and recently my Coolbot started alerting me of a room temp error. The room temperature was too cold and the error message indicated a problem with the Coolbot hardware. The Coolbot sends emails based on parameters that you configure. I am glad I had set the limits of my Coolbot to a room temp of 38F and outer limits of +/- 5F degrees.

When I got to the location of the Walk In, I found the room temp at -7F and the LG window unit was iced up, but still blasting cold air. I assumed there was a problem with the Cool Bot, but using their troubleshooting procedures, I pinpointed the problem to the AC unit and not the Coolbot. Thank goodness the Coolbot had these troubleshooting steps and they were straight-forward and easy to follow.

After a quick look at the control mechanisms for the LG unit and reading about other AC units having similar issues, I proceeded to take the front cover off and locate the control board. The control board is contained inside a metal enclosure and in order to get to it you have to slide the guts of the AC unit out a little ways, in order to access the screws of the enclosure. Well, as luck would have it, I had spray foamed the AC unit into the Walk-in, to avoid air leaks and so I was not immediately able to get the AC unit to slide out. I read online that someone had gotten their unit to start working again and the tech suggested that sliding the unit out and back in, probably unseized the relay contacts, but that eventually the problem would return.

So I proceeded to pound gently on the metal enclosure, of the sides I had available to me, to try and break the contacts free. Sure enough, when I plugged the unit back in and fired it up, the AC unit did not blow cold air until the room warmed up to the set point and then started keeping it where it should be....for a day....then I started getting the email alert of the Coolbot error again. Well, at least I was able to determine that the relays were indeed sticking shut and I would need to replace it.

I found the main control board online and ordered two of them, just in case. My original thought was to just replace the relay on the board, but without having the board in hand, I had no idea what relay to get. I figured I would buy a new board, swap it out and then try to locate the relay and replace it. That would be a much cheaper way to go in the future and would insure that I can run this unit long after parts are unavailable. While I was ordering the main control board, I went ahead and ordered the display board too, just to be safe, in case Murphy struck.

After the new board arrived and I was able to cut through the spray foam and unstick the AC unit, I slid it out and swapped out the board. I'll keep tabs on it and also update this post with any changes. I'll also add additional information, once I find the new relay and replace it, so that maybe someone else can save themselves some headache and money.


CoolBot Pro with WiFi

LG LW1216ER/00 Main Control Board - Genuine OEM


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IslandLizard

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Glad you found the problem and the fix was fairly simple at an affordable price.

Is the suspect relay the one with the 2 lugs on top?
If the issue persists, you could add a contactor to the circuit, largely reducing the current handled by the small relay.
 
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Mike Howard

Mike Howard

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Yes, that component is what I am assuming is the compressor relay, since the three relays directly below it look a little small. Would I remove the relay and solder in a contactor at the same location? I was trying to figure out how I could improve the circuit to keep the relay from welding shut. I was going to go looking for a solid state relay or an optoisolator as an upgrade.
 

IslandLizard

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There are a few ways to insert a heavier duty relay in there.

Use the built-in micro relay (the one that's already on the board) to switch a contactor or a solid state relay (SSR),* which in turn switches the heavy compressor load. The high inrush current is the biggest culprit of welding the contacts together in small switches/relays.

You could replace the micro relay with a contactor or SSR,* but it may need a different voltage and/or amperage from what's on the board, to drive it.

* I'm not 100% sure an SSR can be used for inductive loads (compressor), maybe someone can verify that.
 
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Mike Howard

Mike Howard

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So, I am assuming that I would need a contactor rated at about 15 amps and using a coil of 120 volts, like this Omron Contactor?

I think the hardest part would be finding room to fit a contactor inside the AC Unit housing so I don't have exposed 120 volt lines. Unless of course I mounted everything inside of a project box and mounted that next to the AC Unit.

Going that route I could build a cable with blade terminals on one end to connect to the existing relay and those in turn connect to the coil of the Contactor in the new housing. Then run a new line from the Contactor back to the AC Unit which connects to the existing wires that used to connect to the relay.

Yea, I could probably go that route, While I'm at it, it might make sense to remotely locate the Capacitor as well. Then I wouldn't need to slide the unit out at all if something goes wrong...unless the board eventually goes bad. But then that begs the question of if you wanted to chase the rabbit down the hole and just remotely locate the entire electrical enclosure........yikes. Maybe as a future project I can go that route. ;-)
 

IslandLizard

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So, I am assuming that I would need a contactor rated at about 15 amps and using a coil of 120 volts, like this Omron Contactor?
Yes, 120V, and at 10A nominal draw a 15A contactor would be about the minimum.
But isn't that OMRON contactor total overkill?
I'm surprised the operation of the whole unit (as a room AC) depends on that one single micro relay. ::bott:

Do you think (or know) if it cycles much more frequently in your insulated walk-in cooler, than it would in a regular room?

Have you checked the Coolbot for not causing havoc by continuously cycling, which can/will reduce the lifespan of the compressor too.
Have you set a decent long compressor delay?
 

Bobby_M

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My guess is that the whole system is short cycling due to the relatively high BTU. Something like a 6kBTU would have been plenty for that small space assuming you weren't trying to maintain as high a humidity as possible.

The coolbot solves a few problems that a typical temp controller on a "hot wired" AC would have but the downside is that it still relies on the AC's controller to keep working in harsh conditions.

Yes, that OMRON is insanely overkill. Use this one: Learn more: Eaton/Cutler Hammer C25BNB230A Contactor, 2-Pole, 30 Amp, 120 VAC Coil Voltage: Amazon.com: Industrial & Scientific

You won't need to switch two poles... just leave one of the poles unused. Yes, you can put that in a plastic weatherproof junction box on the wall and just run a short length of 12/4 SJ cord between the AC and box. Two wires are power the 120v coil. The other two wires are the switched compressor hot.
 
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Mike Howard

Mike Howard

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Could be short cycling, looks like its on for 3 minutes, off for about 15 minutes when the cooler is static. In the summertime the room this is in gets fairly hot. I went with the bigger unit because I have a duplicate system that has the 8K BTU AC unit and it runs a lot in summer just to keep up.

Both of these units are in a brewery and at times the door can get opened/closed a lot. Maybe its actually better for the unit to have the compressor running longer, but not on the pocketbook Im sure...;-)

As I understand the Coolbot operation, I dont have a lot of settings to choose from. I could adjust the heater setting to a longer defrost time, but Ive never see it icing up until the relay stuck, so Im not sure that will help.

I would guess the AC is operating a lot different than if it was in a 600 sq ft room, as I would think the compressor would run for a lot longer time than it does in my walk in cooler.

graph.PNG settings.PNG
 

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Mike Howard

Mike Howard

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The Walk-in cooler is in a small room, 12 x 8, that is cooled by a different AC unit through the room wall to the outside. The temperature is kept at 68F in that small room most of the time, but may fluctuate higher in the summer. Before I added that AC unit to cool the room, which I did at the same time we installed the Walk-in, it could get 90F in the summer. I have not had it operating through a summer though, so the jury is still out on that.

I am assuming that since the AC unit is plugged into a standard 110V outlet, that the 25A contactor is more than enough to handle the load. And also that this contactor is beefy enough to not have the contacts weld closed.

I've read online that these AC units have this problem rather frequently and is a common issue. I'm wondering if there is a better board based solution so that I don't have to mount a box outside the unit? I'll do that next time the unit goes bad if I have to, but surely there is a relay that can handle the abuse that is a small form factor.
 
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Mike Howard

Mike Howard

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FYI, these are the replacement boards:

LG LW1216ER/00 Display Control Board - Genuine OEM

LG LW1216ER/00 Main Control Board - Genuine OEM

Coincidentally, both of these boards also fit the LW8016ER model that I have at my other location. It recently had a build up of condensation in the area where the main board sits. The condensation puddled up and came into contact with the lower connector and shorted out both the main board and the display board. I had ordered two of each when my LW1216ER stopped working and I am glad I did.
 
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