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Old 18-07-2019, 08:33   #1
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Wiring and plumbing diagram for 110V fridge with dual boxes

I am trying to figure out how to wire /plum the two box system (fridge and freezer) with 1/3 HP 110V Copeland based condenser. this is R134a based system that at some point during previous ownership stopped working. I know that condenser spent time submerged and for this reason i am replacing the rusty compressor.
Each box has one large holdover plate about 3" thick. They each have dual refrigeration loops. 1/4" discharge and 3/8" suction loops are for 110V copeland based air cooled condenser. There is a tee in 1/4" discharge line with alco solenoid valve right after the split going to the fridge box.
From what i can understand, this setup with one solenoid valve implies that Freezer thermostat controls condenser power (compressor and fan), and fridge thermostat controls only the fridge solenoid that is in the discharge line after the Tee.
So i guess I could run into a situation where freezer is too cold and shuts everything off and fridge is not cold enough and i am unsure how likely that is.
Couldn't i wire it so that both thermostats can power condenser? In that case i could get an acceptable fridge cooling and freezer that is too cold which might be a better option.

What is the standard practice when wiring thermostats with dual boxes?

So far i have pressure tested the plates with nitrogen up to about 60psi with suction line connected to service set valve. Expansion valves(TEVs) are open as they should be. intake screens on TEVs are clean, and bulb/tube seems in good condition. They are original and seeing how new ones are >100$ I am willing to take a chance and evacuate/charge the systems and then if things don't work troubleshoot them.
I will add a bypass around the dryer to facilitate changing them.
Air cooled Condenser has liquid line receiver and service ports on both high and low side. Replacement compressor is coming in this week.
While things are apart should i invest in a new receiver? Do they go bad?
Do i consider adding low or high pressure shutoff switches?

I'm on the dock and i suspect this thing will be running alot, but Second part of this exercise will be bringing the Tecumseh HG-850 loop back to life.
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Old 18-07-2019, 17:54   #2
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

Each solenoid controls the flow of refrigerant to each box, when one or both are calling for cooling the condensing unit should run, as each box hits setpoint, the solenoids close.
There are a few different ways to cause the condenser to switch off when each box has reached setpoint.
Many of our multi box systems typically have a low pressure switch wired into the power input, so when each sol valve closes, the unit pulls down below a preset on the low ps switch and turns off.

When cooling is needed, the tstat causes the sol valve to open and the pressure rise in the circuit causes the switch to close and start the compressor.

I always recommend a Hi Ps safety cutout.

Receivers are pretty tough to kill. You might want to flush it out with the proper stuff for cleaning refrigerant lines, we use Superflush by Highside chemicals.

Put isolation valves on either side of the sight glass/filter drier for easy maintenance.
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Old 19-07-2019, 08:29   #3
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

Quote:
Originally Posted by phorvati View Post
I am trying to figure out how to wire /plum the two box system (fridge and freezer) with 1/3 HP 110V Copeland based condenser. this is R134a based system that at some point during previous ownership stopped working. I know that condenser spent time submerged and for this reason i am replacing the rusty compressor.
Each box has one large holdover plate about 3" thick. They each have dual refrigeration loops. 1/4" discharge and 3/8" suction loops are for 110V copeland based air cooled condenser. There is a tee in 1/4" discharge line with alco solenoid valve right after the split going to the fridge box.
From what i can understand, this setup with one solenoid valve implies that Freezer thermostat controls condenser power (compressor and fan), and fridge thermostat controls only the fridge solenoid that is in the discharge line after the Tee.
So i guess I could run into a situation where freezer is too cold and shuts everything off and fridge is not cold enough and i am unsure how likely that is.
Couldn't i wire it so that both thermostats can power condenser? In that case i could get an acceptable fridge cooling and freezer that is too cold which might be a better option.

What is the standard practice when wiring thermostats with dual boxes?

So far i have pressure tested the plates with nitrogen up to about 60psi with suction line connected to service set valve. Expansion valves(TEVs) are open as they should be. intake screens on TEVs are clean, and bulb/tube seems in good condition. They are original and seeing how new ones are >100$ I am willing to take a chance and evacuate/charge the systems and then if things don't work troubleshoot them.
I will add a bypass around the dryer to facilitate changing them.
Air cooled Condenser has liquid line receiver and service ports on both high and low side. Replacement compressor is coming in this week.
While things are apart should i invest in a new receiver? Do they go bad?
Do i consider adding low or high pressure shutoff switches?

I'm on the dock and i suspect this thing will be running alot, but Second part of this exercise will be bringing the Tecumseh HG-850 loop back to life.
Since Hurricane Hugo 20 years ago I have answered the questions about re commissioning refrigeration systems after being under water. Under water hermetically sealed compressor in refrigerant closed sealed loop systems are rarely damaged other than external electrical Fans, relays, thermostats, coils on solenoids and all wiring. Rust on compressor can be treated and painted. It sounds like you determined instead of refrigerant pressure in system you found water and other contamination. If so I would not recommend restoring the unit. If there is refrigerant in unit and exterior of condensing unit corroded replacing condensing unit and filter dryer would be a good idea.

As to the control of refrigerant flow, controlling it separately with two thermostats and refrigerator temperature controlled by eutectic freeze point and a solenoid valve is the least expensive and far less complicated solution.
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Old 19-07-2019, 11:48   #4
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

I am 100% sure water did not enter the cooling loops. Wiring was badly corroded. Initially, i got deterred by the mess of corroded wires around the relay and start capacitor. I ripped all that out 2 years ago when i was gutting the boat. Replacement compressor comes in today(used, working condition, probably as good a the one i have but not as rusty). Now that i have the holdover plates and condenser coils pressure tested, I bought nitorgen tank and regulator and have the service valve set from 10 years ago when i built the danfos based unit on my old boat, I am going to give this a try.
If it looks like its failing and I run into problems, i will start from scratch and look for a new system.

So with danfoss based DC systems, Controller has labeling and you just follow the datasheet/installation manual and its pretty straight forward where everything goes.
With these, it is not so straight forward and i am trying to figure it out. Seafrost website has good wiring diagrams for their AC units which i was able to use to deduce some wiring intuition.
In a typical 110V AC system with only a start capacitor, I understand there is a relay. You don't want thermostat or high pressure switch carrying full current or startup current. So high pressure switch and freezer thermostat controls that relay.
From what i gather Line(hot)comes to relay input(high current contact). High current Relay output contact goes to start cap. Other side of start cap(assuming non-polarized) goes to start terminal on the compressor. Relay output also goes to thermistor (or overcurrent device on the body of compressor) and then to Run terminal on the compressor.
Earth/Ground is wired to body of compressor and neutral is the terminal labeled common on the compressor.
So start Cap is a transient short and as it charges it reduces current flow in start coil(inside compressor). So it must be high impedance at 60Hz. By then run circuit should take over.
And the evaporator fan or a waterpump if i decide to add water condensing loop, would be wired to run with compressor Run circuit.

Is there anything else that i might be missing?

I am a bit off the beaten path here as everyone is going to 12V systems. But i have a good generator and i am at the dock most of the summer. And restoring engine drive side is in the plans.
I design portable GFCI and arc fault circuit interrupters for one of our clients and i am wondering if having one in the dedicated fridge circuit would improve safety?
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Old 19-07-2019, 15:59   #5
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

I would start with the wiring diagram that applies to the compressor you bought.
Confirm correct start parts, wire as indicated.
Fan and pump run when Compressor starts , though we add an on/off for the h2o.
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Old 19-07-2019, 16:57   #6
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

If the compressor you ordered is mounted on complete condensing unit the start relay devices are there. Connect new 115 volt refrigerator wires with freezer thermostat in series. The thermostat for refrigerator solenoid needs to get its power from the condenser fan circuit power connections. If you do not receive the compressor relay parts you can get a 3 way conversion for the 1/3 hp compressor at under $20.

Use your nitrogen set to less 200 PSI and no higher for leak testing then dehydrate with refrigerant vacuum pump for more than 4 hours, more if ambient temperature is below 75 degree F

For redundancy should generator give you trouble A suggest installing a 12volt to 115 volt inverter.
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Old 14-08-2019, 08:03   #7
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

I am close to getting this thing evacuated and charged.
here is my electrical drawing.
I decided to use Solid State Relay(SSR) to control Compressor, fan and fridge thermostat. We had some leftover SSRs from work and they are very nice. I have a nice heat sink for it as well.
Freezer uses 12V analog thermostat and this is in series with high pressure switch to control input to the SSR. 4V-32V DC
SSR load terminals are 240V 15A rated and it controls 120V load. Fridge thermostat is 120V digital temp controller, and only controls the 120V solenoid coil for the fridge evaporator loop. (buying crap from china like this temp controller scares me as few comments on amazon were that relay failed closed, likely contacts welded shut due to arcing)

I don't remember off hand what the connectivity drawing was on the back of the cover for the three terminals on Copeland compressor(start, Run and Common) and the thermal overload protection. So that part of the drawing is still TBD. Once I go back to the boat, i'll update this.

One question i had is in order to get the system purged, evacuated and precharged, i need to temporarily power just the 120V Fridge solenoid via a separate power strip in order to open the fridge evaporator loop. Is there a better way to do this without running compressor? Then once that is all done i wire it back in before i turn on the 120V 15A breaker.

Second question i had is with respect to Condenser fan flow. Fan Motor wires are not labeled. It seems to me that means there is a 50/50 chance that it blows the wrong way. Fan is positioned between compressor and condenser coils. Should it direct air from or to condenser coils?
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Old 14-08-2019, 17:18   #8
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

Draw the air through the coil first, just make a temp plug for the solenoid with an old cord end and some wire nuts
, looking at the drawing you posted, it also looks like you can disconnect the L1 to the overload itself and still energize the sol coil.
then you can power the solenoid without running the system, I keep a couple with me for this sort of thing...
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