Refrigeration Email I have no good answer for.

[Richard Kollmann]

How would you answer this boater halfway around the World ?
Bought the boat with refrigeration and it will not get colder inside the box than 36 degree C, High pressure 130 psi and low pressure of 12 psi after three running hours. Multiple pictures of gauges sent. Confirming condition also correct TXV installation and its temp sense tube mounting. In follow up I found there was no receiver before TXV in the system.
Is it possible that there is better answer than mine without opening up system and installing a hard to come by Receiver ?.
This was my last response to him.
You still do not understand the relationship of refrigerant differential pressure across the refrigerant flow control device and evaporator temperature/pressure. If you want low box temperature there must be enough refrigerant flow at a low pressure/temperature below 6 psi. Eight psi might be normal for a refrigerator and four psi for a freezer. But the end result can not be reached if TXV or capillary tube can not descend low enough in 30 minutes and continue descending as long as compressor is running.
When a TXV valve is used to control high and low volume flow it must include a liquid receiver to accommodate extra storage of refrigerant when TXV starts dropping pressure in low pressure side of system.
I do not know of a good solution other than installing a receiver before TXV. Adding more refrigerant increasing high liquid pressure might help. Adjusting TXV in to lower pressure will convert halve over to a capillary tube but less effective taking a longer time to reach sired evaporator temps.

[OzeLouie]

Originally Posted by Richard Kollmann

How would you answer this boater halfway around the World ?
Bought the boat with refrigeration and it will not get colder inside the box than 36 degree C, High pressure 130 psi and low pressure of 12 psi after three running hours. Multiple pictures of gauges sent. Confirming condition also correct TXV installation and its temp sense tube mounting. In follow up I found there was no receiver before TXV in the system.
Is it possible that there is better answer than mine without opening up system and installing a hard to come by Receiver ?.
This was my last response to him.
You still do not understand the relationship of refrigerant differential pressure across the refrigerant flow control device and evaporator temperature/pressure. If you want low box temperature there must be enough refrigerant flow at a low pressure/temperature below 6 psi. Eight psi might be normal for a refrigerator and four psi for a freezer. But the end result can not be reached if TXV or capillary tube can not descend low enough in 30 minutes and continue descending as long as compressor is running.
When a TXV valve is used to control high and low volume flow it must include a liquid receiver to accommodate extra storage of refrigerant when TXV starts dropping pressure in low pressure side of system.
I do not know of a good solution other than installing a receiver before TXV. Adding more refrigerant increasing high liquid pressure might help. Adjusting TXV in to lower pressure will convert halve over to a capillary tube but less effective taking a longer time to reach sired evaporator temps.

Ha Ha so you get these enquiries too! EG: "I'm at sea near XXXYZ and my fridge doesn't work, what's wrong with it?" (Now where is my magic wand!!)

A few questions and it just may be possible to be of help, but you may have already asked these...

A: Has this system been working in the past or is it a new 'creation'?
If this system has 'worked' in the past then it is very short of gas. Reasoning: Lacking the availability of condensed liquid, the normal evaporator expansion is not occurring allowing hot gas (not liquid) to be fed into the evap causing the TXV to open wide causing a high back pressure.


B: What refrigerant is it using?

C: Does he have service equipment (Vac pump, detector etc.) and refrigerant.

And like you say it should have a receiver, sight glass and proper filter dryer prior to the TXV but I have seen worse and sometimes they work, sort of!!!

[cr180]

So my expertise electrical, not refrigerant cycle. But 36C =98F. Don’t know ambient air temp at location, but this is essentially zero BTUs cooling. Something fundamentally wrong.

[cr180]

But if 36F, not C, and if ambient air temp in 90s, my experience has been refrigeration can struggle to get 36F. Could be more a function of box than refrigeration cycle!

[cr180]

Or maybe engine room temps affecting box? Question to ask, what is delta T outside box to inside box.?

[RaymondR]

The tubing in some condensers is sometimes fairly large diameter and if the OP's is one of these it may provide sufficient volume to act as a small accumulator.

Theoretically one might have just sufficient refrigerant in the system to provide back pressure through the orifice in the TXV to produce 130 psi high side pressure but only enough going into the evaporator to maintain 12 psi low side without enough boiling off in the evaporator to absorb much heat.

Is he (or she) seeing any frosting on the evaporator and what is the compressor amp draw?

[Richard Kollmann]

Raymond, thanks you are the first to provide good points of advice. Here is additional info, Owner replaced compressor. High pressure out of compressor 1/4 inch after TXV tubing is 3/8 inch, 134a refrigerant, two3 hour test runs lowest low pressure 14 and 12 psi, high pressures 130 and 135 psi, climate temps 85 degrees F. I would like to know if this was the same TXV as on the old compressor.

You may have the answer to not needing a receiver by adding additional liquid refrigerant to condenser. and a sight glass is not necessary when monitoring high pressure level spot.

I ask for present of frost anywhere in system. And why compressor was replaced also capacity of old and new. Also need to know if air or water cooled.

Based on what we know at this point I will recommend adding refrigerant to reach 145 psi. if that does not work to get low pressure below 10 psi allowing return gas temperature to override wide open TXV. The last try will be to adjust superheat reducing opening of TXV orifice to flow of less than 10 psi. Hopefully once TXV takes over control and liquid backs up into condenser lowering pressures and compressor temperatures.

Robert, It is recommended when working with refrigeration to ware protection. There are risks of overheating compressor and excessive high pressure also do not let high pressure exceed 150 psi.
If there were such a thing as Refrigeration Industry Standards for mobile refrigerator, we would be disappointing special interested groups

[Dougtiff]

Reefer syst don't have TXV and capillary tubes, one or the other, pull vacums to 0 on the gauge (suction), if it holds continue to pull suction for at least 2 hours, with evaporator at about 70 deg. F (use heat lamp if needed), break vacume by changing, with in 15 min. Charg to 10 PSI, don't overcharge, it's easy to do, frost line not to exit the box, you can also use a tempt. Pressure chart for correct charge.

[Bowdrie]

Lets see;
130 on high side, 12 on low side, no cooling,,.
Perhaps the presence of a non-condensable in system,, air, remnants of an inert purging gas?

[Grattaway]

Richard hi

TX valve is always a good place for owner to triple check - is capillary ok not broken and well fixed to tube it is sensing
A "cheat" if more refrigerant is needed is to use a strainer or filter in liquid line instead of a "proper" receiver but my first thought is shortage of refrigerant or condensor not doing its job - check liquid line temp

good luck - the art of refrigeration doesnt always align with the science and it gets even harder when you are not looking at the equipment
Wayne

[Richard Kollmann]

Originally Posted by Bowdrie

Lets see;
130 on high side, 12 on low side, no cooling,,.
Perhaps the presence of a non-condensable in system,, air, remnants of an inert purging gas?

That is possible but I normally find non condensable like air cause higher than normal high pressure. Without a sight glass to confirm correct volume you can be correct. I advised Robert increase refrigerant volume till high pressure is 145 psi and warned not to go above that. If adding refrigerant does ot get low pressure below 10 psi in 20 minutes to reduce refrigerant flow through TXV by decreasing valves superheat adjustment this might work. I will also also inquire about vacuum dehydration after compressor was replaced.

[Bowdrie]

Originally Posted by Richard Kollmann

That is possible but I normally find non condensable like air cause higher than normal high pressure. Without a sight glass to confirm correct volume you can be correct. I will also also inquire about vacuum dehydration after compressor was replaced.

You're correct about a non-condensable being present,, and sight glasses are a wonderful device for enlightenment.
Considering the vacuum dehydration;
Perhaps not applicable to this system under discussion, but on a few occasions, while using a very powerful vacuum pump, I have had moisture in a system go thru "sublimation", whereby the moisture changed from a liquid directly into ice before it had a chance to be evaporated/evacuated.
Sometimes it's good to start the evacuation process slowly on the low side while feeding-in a bit of refrigerant, or nitrogen, into the high side to "sweep" the system before immediately vacuuming from both sides.

[Richard Kollmann]

Louie, You might have a point based on your own experiences but I have found that rarely will you find two of the mobile refrigeration systems functioning like a text book if there was such a thing. Some one halfway around the world emailed me for help normally these requests fit duplicate a previous set of problems so I may have made a mistake by asking you and others on forum for help. Normally when the system manufacture is known I look for typical repairs or service bulletins on their web sites or in their manuals I have on file for an answer.

I did follow up with Email as I posted that exceeded normal system operation pressure and temperatures in attempt to force TXV orifice to a achieve super heat resulting in a low evaporator pressure of 10 psi.

Yesterday's feed back produced cooling so I recommended returning to normal high pressure and replacing or cleaning TXV inlet screen.

Thanks Raymond for your help it may require flooding some of condenser to make up for loss of receiver.

[OzeLouie]

Originally Posted by Richard Kollmann

Louie, You might have a point based on your own experiences but I have found that rarely will you find two of the mobile refrigeration systems functioning like a text book if there was such a thing. Some one halfway around the world emailed me for help normally these requests fit duplicate a previous set of problems so I may have made a mistake by asking you and others on forum for help. Normally when the system manufacture is known I look for typical repairs or service bulletins on their web sites or in their manuals I have on file for an answer.

I did follow up with Email as I posted that exceeded normal system operation pressure and temperatures in attempt to force TXV orifice to a achieve super heat resulting in a low evaporator pressure of 10 psi.

Yesterday's feed back produced cooling so I recommended returning to normal high pressure and replacing or cleaning TXV inlet screen.

Thanks Raymond for your help it may require flooding some of condenser to make up for loss of receiver.

So it was short of gas just as I suggested in post 2 ... Quote: If this system has 'worked' in the past then it is very short of gas. Reasoning: Lacking the availability of condensed liquid, the normal evaporator expansion is not occurring allowing hot gas (not liquid) to be fed into the evap causing the TXV to open wide causing a high back pressure.

[RaymondR]

I have learned a lot from participating in these refrigeration threads over the past few years and feel that whilst I have a lot more to learn yet. I may be justified in edging towards an opinion that overall the refrigeration circuit using a TXV could be the more durable of the two systems when used in pleasure vessel marine applications. However this is from a limited experience base as yet limited to only capillary tube systems and may change if I can implement a TXV controlled system and gain some operating experience with it.

Whilst simpler and with fewer moving parts and possible leakage points, the capillary flow control system is dependent upon a very fine balance between compressor output and system refrigerant volume. With the corrosive marine environment and high vibration levels and often extended periods of remote operations common in pleasure vessels this may prove difficult to maintain.

In contrast the extra volume of refrigerant in TXV systems with an accumulator provides some leak tolerance and the compressor speed independent control of flow into the evaporator provided by the TXV being more responsive to flow variations which may occur with low DC voltage compressors and better design to ensure optimum refrigerant volumes in the evaporator could prove the more appropriate system for pleasure vessel usage.