Need help with temp control on Ferm Chamber

[John Kimble]

Here is my conundrum...
I was lucky enough to purchase a large TurboAir glass door refrigerator that is normally $3800 for $200 used from a local restaurant. It is in perfect working order and just the right side for my cheese and salami cave/lager ferment chamber. It has a digital temp control display, but it only goes up to 39 degrees. I want to keep the unit at 50 to 55 degrees.
I control my other Ferm Chambers with an Inkbird ...but when I called TurboAir to ask them if the constant powering up and down of the entire unit through the controller would damage the unit, they said without a doubt it would. They also do not sell a digital control unit to replace the standard one that would allow for for that increased base temperature.
Does anyone know of a solution to replace an existing built in temperature control unit with an Inkbird or another controller so the entire unit does not need to power up and down to reach that 50ish degree range?
Thanks in advance for any help and advice.

 

[day_trippr]

Can you post an image of the wiring diagram for this machine?

Cheers!

 

[John Kimble]

Do you have an email I can send it to? It won't let me upload the PDF file. Model is MSR-23g-1. I couldn't cut it and paste because of resolution. Thank you very much for looking at this for me!

 

[John Kimble]

Took a screenshot. Best resolution I could do.

 

[day_trippr]

Ok, so here's what I think will work.

The compressor and condenser fan are both on the same circuit, while the evaporator fan is on a different circuit (with the door switch). The fridge controller probably does something cute with the evap fan like leaving it running for awhile after the compressor stops, but you definitely need all three elements running whenever the compressor is running, and without complicating things further I've drawn up a simple-but-will-work scheme.

I'll assume an Inkbird ITC-1000 mounted externally for now. If you have a different controller in mind, or somehow want to integrate a controller into the fridge, let me know.

Starting at the ITC end:

- Wire an AC line cord with the black (hot) wire connected to ITC pins 1, 5 and 7, and the white (neutral) connected to ITC pin 2.

- If you mount the ITC in a metal case, connect the line cord green Safety ground wire to the case. Otherwise it won't be used.

- Inside the fridge, remove the connection from the Power Relay to the compressor and condensing fan - the diagram indicates "GY" - maybe Gray?

- Next, remove the wires from both terminals of the Cooling Fan. There's the wire marked "WH" coming from the door switch, and the wire marked "BL" (presumably blue) coming from the controller.

- Now connect the ITC pin 8 (Cooling relay) to the wire marked "GY" (or to the connected "BK" wire) to the compressor/evaporator fan, and to the "WH" wire to the Cooling Fan.

- Then, connect the "BK" wire from the Cooling Fan to the wire shown to the right side marked "WH" (which is the system neutral wire).

With all that done and both the ITC and the fridge plugged into AC outlets, the ITC will control the compressor, condensing fan and cooling fan via the Cooling relay function. Everything else will still be controlled by the fridge (door lights, display if there is one, etc). If you need to add a Heater, wire that between the ITC Heat relay output (pin 6) and the white Neutral circuit...

Cheers!

 

[John Kimble]

You sir, are awesome.
I am going to go over this tonight and tomorrow morning and I will let you know if I have any questions.
Seriously you went way above and beyond. I really appreciate the time you put into helping me here.

 

[day_trippr]

Always happy to help where I can.

I assume you have or have had this unit working. If so there shouldn't be any surprises.
I favor 14 gauge wire for high load hook-ups of this nature. I wouldn't undersize the connection from the ITC to the compressor/condenser fan, though you could go down to 18 for the connections to the evap fan if it makes that easier.

If you're lucky all the wires you need to disconnect and then connect elsewhere use female spade lugs; if so you can buy the male crimp-on version to make your connections to everything but the evap fan to Neutral - you'll need to find a splice point in the white neutral circuit for that one...

Cheers!

 

[ajdelange]

All you have to do is lift the blue wire from the PCB and put a contact from your external controller in series between it and the terminal on the PCB to which it normally attaches. Set the built in thermostat to a low temperature and set your external controller for the temperature you want. The built in t'stat will always have the PCB blue terminal active (connected to neutral) because the temperature in the box will always be higher than its set point. But the external control contact keeps that terminal isolated from the compressor/fan contactor coil until the temperature rises out of the deadband. Use a wide deadband to prevent short cycling.

Note that the external controller's contact is only switching the power relay coil. Thus it does not need to have capacity necessary to handle the compressor and fan motor inrush and running currents but only a few ma. This is one of the advantages over what was suggested in No. 5. The other is that it preserves the relationship between the compressor and door switch whatever that may be. It isn't clear from the diagram. If the contacts as shown in the drawing represent the door closed position then the evaporator fan would not run when the door was closed even though the thermostat called for cooling. This would result in 0 superheat and potential damage to the compressor so the drawing must represent door open. Closing the door then would de energize the GY wire which must signal the PCB that the door is closed so that it handles the evaporator fan and compressor motor appropriately for that condition. Similarly, when the door is open the GY wire is energized so the PCB knows not what to do when the door is open. It would be handy if we knew what that was so if you could observe what it does under normal operation with door open and closed that would be a help.

The arrangement proposed here will do everything except manage the evaporator fan as in the original system. It will perhaps be on more than it would in the unmodified system (because the PCB is always calling for compressor) but it will never be off when the compressor is on.

Keep in mind that you are asking the system to operate outside its design envelope. There may be consequences to this. Head pressure at 55 °F might be higher than head pressure at 39 °F, for example. This would mean more stress but not, perhaps, so much as to shorten life appreciably. Which brings to mind the question "What refrigerant?".

 

[John Kimble]

I will get your answer on the refrigerant soon.
For your solution, when I lift the BLU wire from the PCB, what would I wire that to in series with the Inkbird ITC-1000?

 

[ajdelange]

You would connect the blue wire to pin 7 and connect pin 8 to the terminal on the PCB where the blue wire used to attach. IOW you are putting the cooling contacts in the Inkbird in series with the blue wire. Be sure to enable the PT function (the default of 3 minutes is good) and set DS as wide as you can tolerate (5 °).

One of the main reasons for suggesting this method is that it retains the compressor protection functions related to the door opening and closing, whatever they may be, and brief power interruptions. The Inkbird's PT function protects from brief temperature fluctuations and the large differential setting minimizes the number of compressor starts thus prolonging the compressor's life.

The refrigerant question is mostly a matter of curiosity.

 

[John Kimble]

Would it be something like this?
The blue wire from the PCB goes to the in port on the cool section of the sensor. I then run a BLK hot wire from the out on the cool section to a wire nut connecting to the hot power of the sensor.
Would this work?

 

[John Kimble]

So what you are saying is something more like this?

 

[ajdelange]

Yes, like No. 12.

 

[John Kimble]

Ok awesome. I will do the wiring this weekend and let you know how it goes. I appreciate all the help!

 

[John Kimble]

Gents,
I cracked open the unit to begin....and the wiring diagram is different. I think it's an older model from what I sent you...could you advise on how to adapt the plan for the new wiring diagram.

 

[day_trippr]

Gents,
I cracked open the unit to begin....and the wiring diagram is different. I think it's an older model from what I sent you...could you advise on how to adapt the plan for the new wiring diagram.

I don't see the "power relay" on this version (great idea by AJ on using it earIer, btw) so you'll need to control the compressor directly by the black wire from the pcb to the compressor. Following AJ's philosophy on letting the fridge control the evap fan should still apply, as long as the fridge thermostat is set below your Inkbird...

Cheers!

 

[John Kimble]

So I should cut the BLK wire coming out of the PCB and connect the Inkbird inline with it?

 

[day_trippr]

Yes, figure out which black wire, remove it from the pcb and connect it to your Cool relay output...

Cheers!

 

[John Kimble]

Last question now that I figured out the wiring on the unit.
Do I cut the black hot wire coming out of the PCB and run it through ports 7 and 8 on the contoller? Or do I cut both the black and white wires from the PCB and run then them through 7 and 8 respectively making a circuit loop?

 

[ajdelange]

Take the black wire coming from the PCB that goes to the capacitor and fan motor before it divides (i.e. close to the circuit board). Wire one of the cut ends to terminal 8 and the other to terminal 7 on the InkBird.

As an aside: it is now clear what the evaporator fan strategy is: run it whenever the door is closed.

 

[John Kimble]

Aj,
Ok, got it!
All I have is 16g marine safe wire... will that work?

 

[John Kimble]

It worked!!!!!
You guys are absolutely awesome.
Thank you so much.

 

[ajdelange]

Apparently. Even if you are hanging out with Marines.

 

[John Kimble]

Here it is. Thank you again for all your help, this unit is able to regulate temp and humidity so much better than the mini fridge cave