Mccann Big Mac Troubles, Infinite Seltzer Setup - Beer, Wine, Mead, & Cider Brewing Discussion Community.

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Apr 28, 2021
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Been working on an infinite seltzer setup the past few weeks similar in configuration to many of the guides found here, youtube, and other sites. It is based on a Mccann Big Mac with the tank stored inside a mini fridge, most similar to the setup shown in the below video.

In my setup

Water line flows through a pressure reducer 80 PSI to 40 PSI and intos a 2 stage water filter
From the filter the line splits to the faucet and into the Mccann pump inlet (this is mounted on the wall with the motor)
From the pump the line goes to the tank which is located inside a small mini fridge
I have 100 psi CO2 going into the tank
I have one tank output sealed and the other going into the faucet

I spent the extra money going with a professionally rebuilt / refurbished Big Mac instead of the many cheap untested ones available. Right off the bat when I connected this setup and opened up the water line the backflow valve leaked and water sprayed everywhere. Upon taking it apart it looks like when they "rebuilt" this they tightened the pieces in such a way that it tore the gasket inside. Bought a repair kit from anderson brass and that is now sorted.

The setup worked well for a few days. Until I had the tank get too cold and ice would literally form immediately out of the faucet. I shut it down, emptied the setup, and refilled. I am having an issue with the pump not turning off and filling the tank until the pressure relief spews outs water. The float switch does not seems to shut off the the motor when the tank is full.

I took this assembly apart and the float is clean and moves freely along the shaft.

I tested the reed switch for continuity and was open regardless on of the position of the float or if I had a magnet nearby, however I could measure a difference in resistance. I am not sure if this is the correct behavior.

Re-assembled everything and the motor ran properly during the first fill.

However opening the fridge and makby shaking something turn the motor on and the pump ran till the relief valve sprayed.

Does anyone have any insight on troubleshooting the float switch? My assumption based on the quality of the setup is that the reed switch is failing from age. I do not see anything that would be susceptible to freezing damage if indeed it got cold enough.

The setup is currently in the garage while working out the kinks. The plan is to put it in the first floor integrated into a sink cabinet. But with the risk of the motor continuously running if the switch is faulty I am having second thoughts. Any ideas on a safety mechanism to shut the system down if I get water spraying everywhere inside the fridge and eventually flooding my cabinet? Not to mention all the CO2 continuously coming out of the open relief valve.


Dec 17, 2019
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First off, I'm a bit jealous that you have 80PSI going into your house that requires a pressure reducer. So, some pictures of your setup would help, but if the float switch is open (off) regardless of where the float is positioned the motor would never turn on. If it's closed (on) then it would always be on. I set my meter to 200K Ohms and it displayed 1 (open) when the probes were separate, and likewise when the probes were connected to the switch with the float in the up position. When I move the float in the down position it reads 0 (closed). If you're seeing some resistance in the closed position (>0 but <>1) it might be because of the setting on your meter is too low. A little resistance isn't that unexpected because crap on the probes or oxidation on the switch leads will create it. It is also possible that the problem is in the extension you used to connect the motor on the outside of the fridge to the probe connected to the tank. there is 110 volts (or 220 if you're in Europe) and all the amps required to run the motor go through that wire, so if it is undersized it could have melted somewhere and caused a short therefore bypassing the switch.

Another thing is to make sure that the carbonator tank is completely level so that the float moves freely in the tank, if it sticks it might stay on, and if the refrigerator has a fan in it try and keep the cold air blowing across the evaporator from blowing directly onto the tank and lines as that will help prevent freezing. I just put my whole carbonator in the kegerator I used as seen in this thread and set the thermostat to 38 degrees, it's far enough from the evaporator that the air mixes in the whole refrigerator before it reaches the carbonator but I have seen instances where people put them too close to the evaporator and things froze.

As for water protection from floods, some Lancer carbonators have an automatic shut off feature that turns off the pump after its been running for 5 minutes and has a reset button on them. You should be able to buy one of these control boards and incorporate them into the McCann carbonator inline with the probe, as there really isn't much to a carbonator. This will stop water from constantly being pumped into the carbonator after 5 minutes and once pressure equalizes in the tank the valve should close, unless the pressure relief valve freezes open. Another option is that there are automatic water shutoff valves that do something similar after X amount of time, the downside of these is that it doesn't turn off the motor and that thing will run until the pump seizes.