External temp controller

[macminn18]

I futzed around a bit with the coarse adjustment screw on my freezer, but have had second thoughts. The control is in the front of the freezer, and I'm building a cabinet around it, so if I need to adjust it, I'll need to partially disassemble the keezer. I don't want a door or panel for access there, as it's part of my bar and don't want that to take away from the look.

So my question is how do the external temp controllers work? Do they completely bypass the thermostat on the freezer? Since I screwed around with the coarse adjustment screw, is that an issue?

Leaning towards the Johnson controller, don't really want to do any wiring.

Thanks in advance!

 

[ajdelange]

Yes, they do completely 'bypass' the freezer's internal control in the sense that the freezer's control is set such that any time the freezer is plugged in it will run i.e. as low as it will go. The external controller then switches the 120 VAC to the freezer on and off according as to whether the temperature sensed by its probe is above or below the set point.

Keep in mind that this arrangement will cause the compressor to cycle on and off more than normal and high side pressure will be higher than normal relative to the design temperatures for the unit. This will result in shorter life for the freezer than one would expect were it operated normally.

 

[macminn18]

ajdelange, thanks for the reply. Is there a better alternative that wouldn't negatively affect the compressor?

 

[MrAverageGuy]

I futzed around a bit with the coarse adjustment screw on my freezer, but have had second thoughts. The control is in the front of the freezer, and I'm building a cabinet around it, so if I need to adjust it, I'll need to partially disassemble the keezer. I don't want a door or panel for access there, as it's part of my bar and don't want that to take away from the look.

So my question is how do the external temp controllers work? Do they completely bypass the thermostat on the freezer? Since I screwed around with the coarse adjustment screw, is that an issue?

Leaning towards the Johnson controller, don't really want to do any wiring.

Thanks in advance!

Re: the Johnson A419 controller, I have two of them and am very pleased. One consideration when selecting a controller is, that if you ever decide to use a thermowell (inserted inside your fermenter to measure wort temp directly), the Johnson A419 has a 'fat' (0.25" OD) sensor at the end of the cable - too big to fit in some thermowells. I've heard there are thermowells that will accommodate - but they seem less common.

 

[ajdelange]

ajdelange, thanks for the reply. Is there a better alternative that wouldn't negatively affect the compressor?

Sure. The correct amount of refrigerant of the proper type with the right TXV (expansion valve) and proper condenser and evaporator coils for the application you have in mind rather than the application for which the freezer was designed. IOW, practically speaking, no. But a freezer operated normally should last a very long time. Do what you are planning to do and it will last 2/3 or 1/2 of a very long time. Many people work this way successfully for years. You won't be running back to the store for a new freezer every year or two by any means. Perhaps I shouldn't have been too alarmist.

I suppose one thing you could do is set the dead zone on the controller high. These things work such that the controller switches the compressor on when the temperature climbs to say 40 °F. It then stays on until the temperature drops by the dead zone amount. If you set this to, for example, 5 ° the compressor would stay on until the temperature were reduced to 40 - 5 = 35 °F and then switch off. If you set the dead band to 10 ° then it won't switch off until 40 - 10 = 30 ° is reached and ao on. With a large dead band the compressor will run longer each cycles but sill stay off longer too. Thus the number of run cycles will be less. The thermal mass of the beer will largely intergate out (smooth) the temperature variations.