Rewiring mechanical A/C: Keep compressor on

Hey all,

Bought a replacement A/C unit yesterday that's mechanical. It gets my ferm chamber down to 64^F, but no lower. My fermometer is reading 70^F temps this morning, so I want to rewire the thing to keep the compressor on (doesn't really make too much difference in terms of A/C health, as my temp controller will cut power off once it's probe reaches 62^F inside a 1L bottle of water).

I can't find any wiring diagrams on the specific model I have, it's a wal mart $98 GE one with controls on the left. Is there a standard for which wires control the compressor functionality? I'm very new on A/C wiring, only having rewired my last digital one with the help of a diagram. I just want it to keep the compressor on instead of constantly going on and off.

If you want it on all the time.

Take the controlelr out of the question, wire the hot leads on your wire right to the compressor. When you plug it in, it will be on, problem solved.

NoNothing said:

If you want it on all the time.

Take the controlelr out of the question, wire the hot leads on your wire right to the compressor. When you plug it in, it will be on, problem solved.

Click to expand...

I'm a little confused, or maybe I'm not. Hah. You're saying to just take the hot leads from the A/C temp sensor (thereby cutting the sensor itself off, which is a long metal one) and essentially attach (tape would work) them to the compressor housing? Or do you mean to take the hot leads and splice them both to one of the compressor wires?

There's going to be wires going right into the compressor. Take a picture of them and someone on here will tell you which wires to connect directly to the power. Pralee not a good idea, run it through a switch at least.

Here's a couple images of my A/C unit. The metal lead that goes to the front coils connects directly into the box that has two hot leads entering it from the top.

Ricand said:

There's going to be wires going right into the compressor. Take a picture of them and someone on here will tell you which wires to connect directly to the power. Pralee not a good idea, run it through a switch at least.

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Eh, to me plugging it in is the switch, haha.

What Im saying is cut the leads going to both the compressor and the temp sensor and where the power wires come from the sensor and go to the compressor, just attach the wires straight from the wall to that. overriding any sort of 'control' of the compressor and making it just an on/off depending on if the switch is plugged in or not.

Well that is the thermostat switch. Take this with the disclaimer that I would try this, but you are at risk of ruining your compressor and/or getting shocked if you don't know what you are doing. You are at your own risk doing my suggestions here.

Unplug the two red wires coming out of the thermostat control box and simply short them out. That should just be a thermostat/switch for the compressor. Be sure you have the unit unplugged when you try this, then plug it in and see if the compressor comes on.

Ricand said:

Well that is the thermostat switch. Take this with the disclaimer that I would try this, but you are at risk of ruining your compressor and/or getting shocked if you don't know what you are doing. You are at your own risk doing my suggestions here.

Unplug the two red wires coming out of the thermostat control box and simply short them out. That should just be a thermostat/switch for the compressor. Be sure you have the unit unplugged when you try this, then plug it in and see if the compressor comes on.

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That worked great, thanks! I simply slid the two hot connector plugs together, plugged the sucker in, and the compressor came on and stayed on. I don't think this will be much of a freezing over issue as long as I don't set my ext temp controller to lower than 62^F and make sure all gaps and cracks in the chamber are sealed with foam, right? I'll also put some moisture absorbing substance inside the chamber. If little to no moisture can enter the chamber through gaps and cracks, then freezing over isn't much of an issue, right (as long as the compressor does get breaks, of course).

Lack of airflow and high humidity are your enemies on freeze overs. Make sure the vanes stay clean and free from dust/hair etc to keep the airflow to the max. Worst case, just unplug it for a bit if it becomes an ice ball. Alternatively you could use one of those cheap aquarium thermostats and wire it with thermostatic control to keep the temp what you need it to be.

The other trick, in case anyone cares, is to move the temp probe away from the conditioned space back to where it will stay warm.

Bobby_M said:

The other trick, in case anyone cares, is to move the temp probe away from the conditioned space back to where it will stay warm.

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Can't move this one, it's mechanical. Capillary tube and expanding gas.

Ricand said:

Can't move this one, it's mechanical. Capillary tube and expanding gas.

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I actually did try bending it out to the back side of the unit first...yeah...didn't work BUT, for my last A/C that did have wire leads on the bulb, I extended it which did work.

Damn, just checked it (1 hour after it being on). The temp is down to 62^F, which is good, and means it would have cut off soon, but the device to the left of the compressor was freezing over. I imagine the coils were doing similarly. That's the one drawback from living next to the beach...higher humidity.

Would exchanging this unit for a higher BTU one do better? Does higher BTU's mean colder temps? This one is 5,000. Would a 7,800 one do the trick?

ThreeTaps said:

I actually did try bending it out to the back side of the unit first...yeah...didn't work BUT, for my last A/C that did have wire leads on the bulb, I extended it which did work.

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Yeah, it's too bad that mechanically it comes on when the pressure get's higher, otherwise we could all just nip the tube off and have everything stay on. I wonder if you could take a pair of pliers and squeeze the bulb a bit to increase the pressure without holing it, thereby locking the unit on. Since you are essentially shorting the device out, you should give it a try and report back to the rest of us. Wouldn't take much of a squeeze at all, just a slight flattening I would think.

ThreeTaps said:

Damn, just checked it (1 hour after it being on). The temp is down to 62^F, which is good, and means it would have cut off soon, but the device to the left of the compressor was freezing over. I imagine the coils were doing similarly. That's the one drawback from living next to the beach...higher humidity.

Would exchanging this unit for a higher BTU one do better? Does higher BTU's mean colder temps? This one is 5,000. Would a 7,800 one do the trick?

Click to expand...

A little ice the evaporator lead won't hurt anything, you have to worry about the coils freezing over. Do you have all the covers on it? You've got to get more warmer air moving over the coils to keep them from freezing. A larger unit could/would freeze up as well. Some have used a supplemental fan to move more air over the evaporator coils.

Here is what I have done which seems to finally solve the freeze problem. I cut a piece of open cell foam (1" thick) to cover the front of the AC unit (over coils). I then pointed a fan at the front to blow air through the foam. Two days ago everything was freezing constantly, now it runs great. I've been fighting this battle for 6 months or so.

btw I am using the AC to cold crash @ 35F, at 60F I did not have freezing issues on the coils.

Ricand said:

A little ice the evaporator lead won't hurt anything, you have to worry about the coils freezing over. Do you have all the covers on it? You've got to get more warmer air moving over the coils to keep them from freezing. A larger unit could/would freeze up as well. Some have used a supplemental fan to move more air over the evaporator coils.

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Yeah, my coils are frosting up too. This'll be a fun one figuring out what to do. The A/C unit sits on top of the chamber, which has a door cut out, hinged up ward, and resting on the front edge of the A/C unit. The sides of course have insulation board. So, there's not much room to work with, and I'd have to hang a fan from the underside of the hinged door, cutting off the airflow into the chamber.

Any ideas?

Alright, so I removed the front cover of the A/C unit to maximize airflow to the coils. Then I filled every crack and gap with GreatStuff, so it should be pretty air tight inside. Then I placed 3 DampRid buckets inside the chamber (up on the top shelf, two on ground level). Let's see how this works. If it still doesn't fix the problem, I'll probably buy a dehumidifier and place it inside the chamber.

Am I missing anything that I should be doing here?

Still getting frost on the coils and mesh.

Here's a couple pics of my AC unit. Since I'm not super familiar with the airflow, I'm wondering if the cold air coming out the top gap is being immediately circulated back around and sucked into the coils and mesh. Could that be causing the frost so quickly? If so, would simply separating the top gap where air comes out from the coils and mesh with a 45 degree angled piece of cardboard help to resolve that? I could even rest a fan on it's back and point it up into the underside of the cardboard, directing the air on the mesh while not interfering with the A/C air coming in.

EDIT: I went ahead and did that: folded some cardboard as a "ramp" for the cold air to fall down and into the chamber with, while makeing it so that virtually no air conditioned air can directly go back into the coils and mesh. Then I put a desk fan on its back and aimed it up into the underside of the ramp, so more airflow goes through the coils and mesh. We'll see how that goes. (there's a shelf about 7 inches below the bottom of the A/C, FYI)

I think I'm talking to myself here. Hah.

Just checked on it again, and even though it was frosted up a bit (not as much as before), the ambient temp was at 50^F. Wow! That cardboard ramp sure improved the air flow down to my fermenting wort! So now I upped the high limit threshhold a bit to turn the A/C off, to 65^F (was at 62^F, but I'm sure the bottle of water hadn't gotten to that temp yet) to let the mesh defrost. The fermometers both said 66^F, so I'm sure it'll be fine from now on.

Here's crossing my fingers...

Just for anybody who may be reading this, doing what I did works perfectly. Take a piece of cardboard, affix it to separate the air conditioned air outflow port from the mesh and coils at roughly a 45^ angle, then direct a fan up to the underside of that cardboard (which will then feed all air from the fan into the mesh and coils). I've set my ferm chamber (roughly 50 cubic feet) to 58-60^F and it's holding well. Furthermore, not once has there been even the slightest sign of anything frosting up on the A/C unit, and the chamber cools to the target temp quicker than it ever has before (since the air conditioned air can't immediately get drawn back into the unit.).