Grunert R12 Fridge Compressor

[Bowdrie]

Originally Posted by Bermuda Forte

Can the two sets of tubes be joined together? Would there be any value to doing that?

The problem with joining the 2 sets of tubes in series is one of flow capacity/flow restriction.
The tube set for the engine drive is, (appears to be,) 1/2in size, whereas the
one that was for the 12V system looks like 3/8ths.
The 3/8ths lacks the flow rate needed for a high-hp unit, and will result in un-wanted pressure drop across the evaporator.
Among some other negative effects this causes the expansion valve to throttle down to soon, this causes the compressor to pull-down to a lower pressure to soon in the cycle, (in effect the TXV gets "fooled" into behaving as though the evaporator is colder than it really is,) and this messes with the ideal superheat range setting, (there are externally equalized valves that can overcome a measure of pressure drop,) but they are generally outside the realm of a system such as yours, (being more suitable for constant speed units).
Some techs may say to re-solder the tubes so that the 2 tube packs are in parallel, but it's of little gain.
The 3/8ths tube pack is likely much shorter in length and has a lot less surface area to absorb heat, being designed for a fractional hp unit.
It would be my inclination to leave well enough alone.
The 3/8ths tube pack(s) will come in handy should you ever decide in the future to add an auxiliary system, (1/4hp 120VAC air-cooled comes to mind).

[Bermuda Forte]

Thanks all for your replies with help on my Grunert engine drive system. Is there a big difference in compressor brands? I don’t find any available true Sanden 505 (S9056 looks like the best match with charging ports). I see a lot of ones that say “will fit” and I’m concerned they may be Chinese knock-offs and poor quality.

[Bowdrie]

Sanden/Sankyo/Diesel Kiki, all seem to be the same unit, but it's been a few years since I've installed one.
Weren't they all made in Japan?
They were all available with different cylinder heads to suit various hose fittings and applications.
Before you install it, drain the oil charge into a graduated cup, (or some way of measuring the oil quantity).
Re-fill with oil that is assured of being compatible with R-134, (or your chosen refrigerant).
Add ~1>2 oz. of oil beyond that.
Some of the oil charge is always circulating along with the refrigerant.
In auto air-conditioning service the temps are much higher than in a freezer application and the gas velocity thru the evaporator is quite high, (also the evaporators are relatively small,) this assures adequate oil return in service.
In freezer service the return gas velocity is much less, and condensing temps much lower, and as such the oil has more of a tendency to try and separate out from the refrigerant in the evaporator.
This is why we like to add a bit of additional oil in the swash-plate compressors, they don't have the large reservoirs of oil that the old reciprocating Yorks and Tecumseh models had, (even they needed additional oil when used with large/multiple evaporators.
PS. There are techniques for checking oil level after the system has been in service for a few cycles that we can discuss later on, assuming that there are service valves that allow the compressor to be isolated from the rest of the system.
PPS. It turns out that Grunert still makes the style of condenser that you have, (or one that is very close).
I was pleasantly surprised at that.

[Bermuda Forte]

Gents - do you know how I spec a new TXV for the selected Sanden Compressor?

It’s an SD7H15, 155cc.

My auto mechanic that will charge the system asks, what is the HP?

[Bermuda Forte]

[Bermuda Forte]

[Bermuda Forte]

Old R-12 Sporlan TXV is shown in pic.

[wsmurdoch]

I can not tell you what you need, but my engine driven system with a Sanden SD5H14 model S6664 compressor uses a Danfoss R134A TN2 valve with a No 3 orifice. The sensing bulb is near the top of the horizontal low pressure copper tubing leaving the eutectic plate set in thermally conductive grease, wrapped tightly with copper foil, and insulated to give the fastest response to temperature changes.

https://assets.danfoss.com/documents...3en-001401.pdf

[Bermuda Forte]

Thanks for the replies all. I’m also on another similar thread but I’ll post here as well since I appreciate all the help I can get.

The old compressor was larger than the typical ones being offered by SeaFrost. RParts, as recommended by some, was not able to help and referred me to a Sanden distributor.

The old compressor was a Tama Seltec 150 CC and the closest match for fit and size is the SD7 (#4664).

I read the advice about starting the compressor at low RPMs, something I never did over the course of 25 + years operating it, and I’ll be mindful of this now and in the future.

As for running, the pulley sizes are pretty close to 1:1 and the Perkins diesel is at about 1800 RPM during normal cruising speed. Is that too high? The Sanden data sheet suggests speeds of 4,000 to 6000 rpm but I assume that’s for running a big truck AC system.

A local refrigeration guy found a replacement TXV for me to replace the old R-12 Sporlan one. Cost almost as much as the compressor!

One thing I’m having trouble with is finding new hoses. And do they need to be so big? Fittings are #10 (7/8”) suction low side and #8 (3/4”) discharge high side. The system copper tubes are 1/2” and 1/4”.

Since my compressor has the capacity, might it be time to consider joining the abandoned tubes from the old secondary system and running them in parallel?

I don’t have access to nitrogen to blow the system down but I have a flush kit I used on the condenser with denatured alcohol. Do you think I should run the alcohol through all the holding plate tubing and then evacuate with the vacuum pump?

I have a new Sporlan C-082 dryer.

The accumulator is original. I cleaned it up and installed the new HP cut-out switch I got from OceanOptions, the folks the original system came from. Do I need to try and get all the old oil out of that reservoir? It’s been dripping out on the bench after I removed the dryer.

Thanks in advance!

Getting close to start up!

[Bowdrie]

Originally Posted by Bermuda Forte

I read the advice about starting the compressor at low RPMs, something I never did over the course of 25 + years operating it, and I’ll be mindful of this now and in the future.

As for running, the pulley sizes are pretty close to 1:1 and the Perkins diesel is at about 1800 RPM during normal cruising speed. Is that too high? The Sanden data sheet suggests speeds of 4,000 to 6000 rpm but I assume that’s for running a big truck AC system.

A local refrigeration guy found a replacement TXV for me to replace the old R-12 Sporlan one. Cost almost as much as the compressor!

One thing I’m having trouble with is finding new hoses. And do they need to be so big? Fittings are #10 (7/8”) suction low side and #8 (3/4”) discharge high side. The system copper tubes are 1/2” and 1/4”.

Since my compressor has the capacity, might it be time to consider joining the abandoned tubes from the old secondary system and running them in parallel?

I don’t have access to nitrogen to blow the system down but I have a flush kit I used on the condenser with denatured alcohol. Do you think I should run the alcohol through all the holding plate tubing and then evacuate with the vacuum pump?

I have a new Sporlan C-082 dryer.

The accumulator is original. I cleaned it up and installed the new HP cut-out switch I got from OceanOptions, the folks the original system came from. Do I need to try and get all the old oil out of that reservoir? It’s been dripping out on the bench after I removed the dryer.

Thanks in advance!
Getting close to start up!

When first starting the cycle with un-frozen plates the TXVs are wide open and can take advantage of a compressor speed in the 1,600>1,800 rpm range, but as the solution in the plates starts to freeze the speed needs to reduce to keep the compressor from pulling down to lower than optimum pressures.
As you near the end of the runtime the sight glass pretty much fills-up and at that point, (with your large capacity compressor,) an rpm range in the ~1,000>1,200 range is beneficial.
Yes, an AC unit is a whole different ball game and in AC the low-side flow rates are much higher, (the AC basically operating as a flooded low-side, and that's the reason they use quite large suction accumulators).
You mentioned "A" TXV, did not your system use two TXVs, one for a freezer plate and one for a reefer plate?
IIRC, that compressor uses a 5/8ths flare for the suction and a 1/2" size for the high-side?
If so than those are the size hoses to use.
Adding the other 3/8ths evaporator tubes in parallel won't gain but little, it's like resistors in parallel, the lower resistance, (and pressure drop,) across the big tubes means that they will take the lions share of the flow, and they have the surface area to use it.
You can use alcohol to flush the tubes, blow out with air, then evacuate.
Yes, flush the accumulator, you don't want any of the old contaminated oil anywhere in the system.
"Bridge" the filter connections and do the initial evacuation, (getting the alcohol/moisture/contaminates out before installing the new filter.
Then blow some refrigerant thru the system, (from high-side to low-side to give the system a "sweep", then install the new filter and do a good evacuation before charging.
The idea being to get the system clean and dry before putting the new filter-drier in.
Don't forget a couple extra ounces of oil.
When first fired-up run the compressor at slower speed while you check everything over, water flow/leaks/abnormal noise/high and low pressures, etc.
The sight glass should NOT be full at the start>middle of the run cycle, as the TXVs start to throttle then the glass will show a rise, and at the end of the cycle there should still be a little "void" showing.
It's a bit of a balancing act, water temps will change high-side pressures and affect the amount of refrigerant that the system will hold, and superheat adjustments will affect low-side pressures along with sight glass levels, particularly towards the end of the run cycle.
The tech guy will know.

[wsmurdoch]

Adding to the above....

At the first startup you might want to turn the compressor a few turns by hand to be sure that there is no oil in the cylinders before the engine has a go at it.

On later starts, after standing cold, the refrigerant in the system will migrate to the coldest place in the system (the cold plate) where the pressure is the lowest. At startup the TXV will be open, and the compressor will be sucking that refrigerant out of the cold plate. The TVX will be letting more liquid refrigerant enter the cold plate. The cold plate pressure will be dropping, so the refrigerant will be boiling and cooling the cold plate and the suction line to the compressor. As the suction line (and thus the TXV sensor bulb) cools, the TXV will start to close limiting amount of liquid refrigerant entering the cold plate. From that point on the TXV will control the amount of refrigerant entering the cold plate to hold a constant leaving superheat.

At startup watch for frost on the compressor suction line advancing to the compressor inlet. Don't let frost appear on the back of the compressor. The frost is a fair indicator of the presence of a liquid/vapor mix, and you don't want liquid getting into the compressor because the compressor can't compress it. You can control the extent of frost by changing the orifice in the TXV, turning the superheat adjustment screw in the TXV, and by the placement of the TXV sensor bulb on the cold plate suction line and its thermal contact with the cold plate suction line. The orifice limits the flow through the valve when it is full open. The superheat adjustment screw changes the temperature at which the valve opens (1/8 turn is a reasonable increment). Good thermal contact between the sensor bulb and the suction line will make the valve operate faster in response to changes in superheat. The sensor bulb should not be on the bottom of the suction line where it would be measuring the temperature of any oil flowing in the system rather than the refrigerant temperature.

[Bermuda Forte]

Rebuilt the filter dryer receiver assembly with new HP cut out switch and installed the recommended bypass. Flushed out everything with a little alcohol. Per recommendation, I’ll vacuum down the system before installing the filter.

I’d like to confirm the amount of PAG oil I need to add to the system. I’ll drain and measure it.

Next step, install the expansion valve. I’m reading the instructions for the TXV supplied by a local guy. Apparently. He wants me to change the head to the one he included. It’s all new to me.

Thanks guys!

[Bermuda Forte]

[Bermuda Forte]

Cool! And and I mean cold!

Everything refurbished and reinstalled; new Sanden compressor, belt, hoses, filter/dryer, HP cut out switch and TXV.

Flushed really well with alcohol, vacuumed down for about 45 mins, turned over compressor by hand a few times, added 22 oz 134a, fired her up and she’s cold! Just running <1000 rpm. Back in business.

Thanks to all. I couldn’t have done it without your encouragement, advice and experience.

[Bowdrie]

Good for you.
Monitor a few cycles, if your sight glass has a moisture indicator in it watch for any change of color, 45 min. is a fairly short vacuum period for a bigger dual plate system.
Should be a darkish green, if it goes to a lighter green, you're still in the safe range but if it tends towards any "yellowish" tint there is still some moisture present.
Would not be unusual if some fussing with superheat is needed to dial-in the frost back while also watching pressures and sight glass level, a bit of fine-tuning if you will.
Sounds like you'll be able to enjoy a cold beer, or several.