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Old 18-07-2019, 09:33   #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, 18:54   #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, 09:29   #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, 12:48   #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, 16:59   #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, 17:57   #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, 09:03   #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, 18:18   #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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Old 18-08-2019, 18:59   #9
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

So I was able to pull a vacuum. Temperatures were in the high 80s today and vacuum pump ran for about 5 hours. I got 1 full 12 Oz can of r134a discharged into the suction side. Then I started the system and let out another half can. It's been running about 3 hours and boxes are getting cooler. High pressure was creeping up to about 195 and low was in the 30s. So I let a little out to get the high side to remain at 175psi. Low is at around 25psi. At this point temp is dropping in the fridge. My digital thermostat started at 87, ouch, at 6:30pm. It's now 3 hours later and it's 71. High pressure line is hot, almost too hot to the touch. Seems that condenser fan cools it but it still feels warm. And low side is getting condensation on it.
I'm at the dock and I don't really care how much this runs for now. How hot should discharge line be? About 18" of it runs through fridge box before expansion valve and it feels warm to the touch. Almost like it's heating thw box. Should I insulate that section in the fridge box? Same happens in the freezer but about 12" of it is in the freezer before expansion valve. I'll let it run overnight and I'll see where I'm at. Now I am really wishing I put a water cooling loop. How hot is too hot for top of compressor? Condenser fan is definitely pulling air through coils and blowing air across compressor.
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Old 19-08-2019, 05:37   #10
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

With both solenoids open at the same time and I assume both refrigerator and freezer evaporators low pressures equal at 25 psi that is one problem and high pressure more than 50 psi higher than normal is another problem. Low pressure of 25 psi refrigerant flow will result in temperatures equal to low temperature air conditioning not refrigeration. Ten minutes after compressor start up I would think both TXV would deliver less than 15 psi. And in less than 30 minutes there should be a spread in evaporator low pressures. What method are you using to operate refrigerator evaporator at 6 to 10 psi while freezer evaporator at 3 to 5 psi? The typical two evaporator temperature designs would use a Low Pressure Regulator in refrigerator evaporator return line.

A guess at why high pressure is to high is, too much refrigerant in system. There is a receiver refrigerant tank installed in this unit?
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Old 19-08-2019, 07:34   #11
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

Yes i have a receiver, parker PR3083-8-2.
Fridge has FJ-1/4C and i cant really make out what the model is on the freezer TXV. Its the top one in picture below. This pic is old. now the line from TXV to plate is frozen and so is the plate.

Return lines come to a tee outside of the boxes, before heading back to compressor. Compressor ran overnight and freezer is cold, it froze two large freezepacks (8.8"x11"x1" volumes), the kind you put in a cooler to keep stuff cold at the beach. I left them at the bottom.
Fridge has a digital thermostat and its showing 46F. but sensing thermistor is at the top. Plate is getting frozen at the bottom but top still has wet moisture on it. Small section of pipe between fridge TXV and plate also has ice on it.
I took some IR thermometer measurements this morning. Compressor top was at 160F and discharge line right at the exit was hottest point at 186F.
I don't have the PSI readings this morning as i took the gauge off.
What is the ideal low side pressure?
Im getting some insulation today and will start the unit back when i get back home.
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Old 19-08-2019, 07:42   #12
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

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Originally Posted by Richard Kollmann View Post
The typical two evaporator temperature designs would use a Low Pressure Regulator in refrigerator evaporator return line.
Nothing was there, as i said, return lines (3/8") were just joined at a tee and went back to condensing unit.
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Old 19-08-2019, 07:59   #13
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

The temperature of line coming out of compressor to condenser is going to be very hot at times. The refrigerant line temperature coming out of condenser and going to the dividing T fitting is important, what is its temperature now that plate is frozen? Check temperature after condenser and again before the T fitting. Some receivers have a King valve on their outlet line if so is it fully open? Sometimes this valve is closed when replacing Compressors?
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Old 19-08-2019, 08:14   #14
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

The bottom txv valve looks like the top is close to failure, when they get real rusty like that the end is near. make sure the sensing bulb is clamped to the suction line at 10 or 2 o'clock, not on the bottom.

Incomplete/partial evacuation can leave non-condensable air in the system, this will occupy the condenser and cause high pressure/ low capacity.
Are you sure you pulled a good vacuum?
I usually pull a system down for 12 hours minimum, then break the vacuum with dry nitrogen, and evac one more time to 29.9 inhg.

Richard is 100% correct, the high pressure line, after the condenser, when the boxes are cool, should not be hot at all, maybe a little warmer than ambient, but certainly not hot.
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Old 19-08-2019, 08:26   #15
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Re: Wiring and plumbing diagram for 110V fridge with dual boxes

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Nothing was there, as i said, return lines (3/8") were just joined at a tee and went back to condensing unit.
If system worked before then the Capacity of TXVs are at different settings. I have designed boat holding plate Hybrid systems that way before but your unit now with only one 1/3 HP compressor will take many hours running time the first day.
So the only problem to address is the very high liquid refrigerant pressure.
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