Superheat

[subzero*psia]

Okay, lets assume everybody knows how to calculate evaporator superheat on an expansion valve system. These being givens: Low Temp = 4 to 6 degrees F. Medium Temp = 6 to 8 degrees F. And High Temp = 8 to 10 degrees F.


Here is one that confuses alot of techs and will create an interesting debate I think.

How many degrees superheat should you expect to see with a capillary tube system that is operating correctly, and why?

(Sorry, I know alot of you use C and K degrees.)

[Dan]

Interesting question. Quick answer, 10 deg F. Now, how do we measure it?

[subzero*psia]

If you are working on a high temp unit this would be good. Measure your superheat at the end of the cooling cycle and you should get similar results to superheat readings with an expansion valve. The difference is the amount of liquid in the evaporator coil is not constant on cap tube systems. The correct superheat reading is only attained at the end of the cooling cycle when the evaporator is at least 2/3 flooded. If you take a superheat reading in the beginning of the cooling cycle you may see as much as 20 to 45 degrees depending on the application and space conditions.

These are the superheats I typically look for and see on cap tube systems;

Low Temp: 4 to 6 degrees F.

Med. Temp: 6 to 9 degrees F.

High Temp: 9 to 12 degrees F.

Actually I see them cycle off at the very low end of these ranges which is nearly identical to superheats seen with an expansion valve system. Anything above or below these and you might want to look for other signs that may cause your reading to be off before you suspect the refrigerant charge.

[subzero*psia]

To measure evaporator superheat, get your low side pressure reading and convert it to dew point temperature, subtract from that the actual evaporator outlet temperature reading (taken with a probe), and the difference is your evaporator superheat.

To measure suction line superheat take two physical temperature readings... evaporator outlet and again approximately 6 inches from the compressor inlet. The difference between these two is your suction line superheat.

To measure compressor superheat (all superheat prior to the compressor) get your low side pressure reading and convert it to dew point temperature, subtract from that the compressor inlet line temperature. The difference is compressor superheat, [not to be confused with heat of compression which is work added (kinetic energy adding more superheat) to the already superheated refrigerant.]

Note, you will get negative numbers depending on how you perform your calculations. I cheat and reverse the formula... same thing but less confusing.

Thanks for posting Dan, jump right in here!

[Dan]

I think the key information in your answer is to only pay attention to superheat when the refrigerator approaches a satisfied condition. When I was learning the trade, I did a lot of home refrigerator repair. It was not uncommon to have a unit with a very small leak. I would charge it up paying no attention to weighing in the charge. It astounded me how much refrigerant I had to remove once the system reached temperature. And how many trips it took to get the charge right utilizing the frost line method.

Dan

[subzero*psia]

Yes, the suction line superheat reading is a delta T. It is just another small piece of information which can help isolate symptoms. Its not often that you see a tech take it but it can be handy. Say perhaps you have been replacing compressors and you have determined your evaporator superheat is correct, this could help you determine why you have the too much or too little compressor superheat, what your problem is and perhaps specifically where your problem is. It will definitely give you more ideas on what the actual problem could be, perhaps pipe sizing, insufficient insulation, an outside heat source, a liquid injector or hot gas valve isn't seating properly, etc. The more information you can gather, the more accurate your diagnosis will be.

I generally look for evaporator superheat and compressor superheat at the same time, then subtract the evaporator superheat from the later to acquire my suction line superheat if I am looking specifically for it. Suction line and compressor superheat are critical and yet it is often overlooked by even the most experienced. I believe that "at least" 20 to 30 percent of all compressor failures could be avoided by checking superheats and correcting it respectively. I think that most compressor manufacturers just expect it and exchange them under a customer satisfaction policy. But we pay inflated prices to cover these type change outs too.

"Do it right or don't do it at all, and hang in there Its almost Monday!" LOL!!!

[subzero*psia]

Nice Link, you should consider writing a book.

[WebRam]

Hey Dean,

I think Marc is almost there but time could be a factor

eh Marc

[dan wong]

questions for you superheat experts, what is the best way to check a system with a single compressor with two or more evaporator? more to the point- how does one go about adjusting superheat on individual evaporator?? medium temp cabinet (35F-40F) dan

[Edited by dan wong on 21-04-2001 at 11:11 AM]

[subzero*psia]

Well, are both evaporators performing the same application? If they are the same application you can simply use TXV's on both and measure the superheat as previously described in this thread. You should measure each coil outlet seperately.

If one coil is for a low temperature application then you will need an evaporator pressure regulator valve on the outlet of the evaporator coil of the medium temperature application to maintain a minimum evaporator pressure even while the freezer is at a lower pressure and calling for cooling.

Even if both evaporators are performing the same type application or not, each circuit must have its own temperature controlled liquid line solenoid. If you don't have a solenoid in each circuit, no matter what type of application(s), you will flood at least one circuit at different times depending on the frequency and amount of loading being subjected to each coil. It will not always be the same circuit that gets flooded if you don't have LL Solenoids on each circuit either, due to demand loading.

[Gary]

I agree with all of this, Dean. I would only add that a prerequisite to adjusting superheat is ensuring that there is solid liquid at the valve inlet.

In reference to your earlier post, I use compressor superheat as a primary trouble shooting tool, looking at TXV superheat only if the compressor superheat or other clues indicate problems upstream.

Gary
http://www.gatecom.com/~tmethod

[dan wong]

continue from my previous post.
The unit is a cold food storage with a counter top, commonly used in restaurant or pizza prep-table. both evaporator perform same function, medium temp. TXV, originally, a DANFROSS 1/4T internal eq. valve. I changed it to Sportland 1/4t balance port, internal equalize, does not have LL solenoids, evaporators simply hook up in parallel, suction line in parallel with a single line return to compressor. This is the way it came out of factory. unit is old, no tag avaible to identify manufacturer or amount or charge.
Original problem: from time to time, one or both evaporator will ice up completely, changing the txv did not solve the problem, I've adjusted superheat same proceedure as decussed on post here, situation is better but not solved(I set it to 18F sh) I replace the temp control with a low pressure control, make the TURN-ON and TURN-OFF wide, that seen to work ok now.
my question is, since I am taking pressure reading at the compressor-which is common to both evaporator-not knowing if one is over feed or under feed, by taking temp at outlet of each evaporator, It is not accurate adjustment, How can I make an accurate ajustment with this type of set up? dan

[Gary]

For starters, assuming the coils are not plugged with dirt, the original problem was not coils icing, but rather coils failing to fully defrost on the off cycle. (I have found this to be a particular problem on undercounter systems that have been converted to zeotrope refrigerants.)

This was controlled by the "on" setting of the original thermostat, and is now controlled by the "on" setting of the pressure control. Best way is to raise the "on" setting, watch the coils defrost fully, then very slowly lower the setting until the unit comes on (then maybe back up just a touch). Adjust the "off" setting to achieve desired box temperature.

If you adjusted the TXV superheats at the coil outlets, then the outlets should have near identical temps. I'm not sure why they wouldn't.

18F coil outlet superheat is too high. It should be more like 8-10F superheat. These should be re-adjusted. The pressure control may need to be re-adjusted after changing the TXV superheat.

It should be kept in mind that the problem is very rarely TXV superheat adjustment. The vast majority of such adjustments I have made is following up technicians who should not have messed with the valve in the first place, then finding the real problem.

Hope this helps.

Gary
http:/www.gatecom.com/~tmethod/

[subzero*psia]

Gary is right about this Dan. The superheat spring rarely if ever needs adjustment. Personally I look for a superheat of about 6 to 8 degrees on a medium temperature application.

You mention that the coils completely ice up at different times. That goes back to each circuit requiring a liquid line solenoid and temperature control for that space each circuit is trying to control.

A question... you said the unit is old but still original. Is there a liquid reciever tank? If not then the TXV's were installed in the field. Rarely do I find undercounter refrigeration with TXV's from the manufacturer these days... they all want to install captubes and adjust the lengths to make them work. Also what type of product is being placed into these compartments. Watch your customer to see exactly how they use them... it may provide an answer also since we have to assume that this exact system had always operated correctly until now.

Here is one possible way that I DON'T RECOMMEND to get close without adding parts. Close both TXV's, carefull not to close them too tightly. Attach your thermo couples on the evaporator outlets and manifold gauge to your hi/lo access fittings. Start the system, adjust/open ONE of the TXV's until you get the proper suction pressure and superheat reading (record the number of turns you made on the TXV). Go to the second TXV and begin to open it VERY SLOWLY, as you approach the number of turns you took on the other valve... keep an eye on the suction pressure, if it rises and stays up then you have opened the second valve too far! Without being able to completely control each circuit you are going to waste ALOT of your time and possibly damage the system.

With that said...

By not having the liquid line solenoids, one compartment may be calling for cooling while the other is too cold already... without the LL solenoids, you will get exactly what you are experiencing... an iced up coil, first one then the other will follow. A sight glass in the main liquid line would help too.

In order to properly test each circuit you need the LL solenoid valves etc. It is the only way to have one active circuit and one inactive circuit.

Test: after installing temperature controls and LL solenoids, disconnect/adjust temperature control so one solenoid won't open while the other is enegized/open and the opposite circuit is cooling... check suction pressure and perform superheat calculation on the active circuit (Adjust only if absolutely necessary). Reconnect or adjust temperature control to activate the other LL solenoid, watch the suction pressure you should see it change and if you have a sight glass in the main line it will bubble only momentarily... perform a superheat calculation. If the TXV's are not matched you will see your suction pressure is not where you want it, and your superheat will be off on at least one circuit. I have experienced exactly what you are going through... only I had 3 heat exchangers to deal with, save yourself some time and grief... put in the LL solenoids and temperature controls and cycle the condensing unit with your low pressure control.

[dan wong]

Thank all of you for your response.

Currently, the unit is working ok, been working okay for about 6 months now. what I did was ajusted each txv same amount of turns, then fine tune it a bit. at this time I don't want to mess with it, but would like to know how other (experts)do it.

Dean, cold table has 4 doors in a chinese restaurant,kitchen temp approx. 90-95F. door are open at random, often during lunch & dinner hours, It is original equipments except for the compressor, does have receiver. not practical to add liq. line solenoid due to space limitation and difficulty of job. superheat lower than 14F will have a thin layer of ice on bottom of evaporator, restrick air flow.

Would this work? if I disconnect the fans on one evaporator, Let it ice up, causing TXV to fully close, then I can adjust superheat on other evaporator, one evaporatior at a time. what do you think? dan

[Edited by dan wong on 23-04-2001 at 12:27 AM]

[Gary]

Dan, at what point are you taking the temperature reading for your superheat? Coil outlet? Common suction line? Near the compressor inlet?

Gary
http://www.gatecom.com/~tmethod/

[dan wong]

Originally posted by Gary
Dan, at what point are you taking the temperature reading for your superheat? Coil outlet? Common suction line? Near the compressor inlet?

Gary
http://www.gatecom.com/~tmethod/

Pressure gage on compressor suction service valve (reading is common to both evaporator), Temperture clamp probe at suction line at bottom of evaporator, just outside evaporator housing. (I use the CPS temp-seeker T-250, clamp are wrapped with insulation.)

[Dan]

Originally posted by dan wong

Original problem: from time to time, one or both evaporator will ice up completely, changing the txv did not solve the problem, I've adjusted superheat same proceedure as decussed on post here, situation is better but not solved(I set it to 18F sh) I replace the temp control with a low pressure control, make the TURN-ON and TURN-OFF wide, that seen to work ok now.
my question is, since I am taking pressure reading at the compressor-which is common to both evaporator-not knowing if one is over feed or under feed, by taking temp at outlet of each evaporator, It is not accurate adjustment, How can I make an accurate ajustment with this type of set up? dan
[/B]

Most undercounter refrigerators I am familiar with have defrost timers. I recall older designs that did not, and I added timers to them. All commercial refrigerators should have scheduled defrosts. I highly recommend a defrost timer if you don't already have one.

But for sake of discussion, I like the input you have received, after asking some good questions. It makes for fine theoretical discussion and wonder. The manufacturer in me says that you are poking your head into things you shouldn't. The tech in me is with you all the way.

But let's step back. Was the only problem you had originally, that one coil or another or both were icing up? If so, why did you choose to change TEV valves? Why not open up the low pressure control then, as opposed to after you performed major surgery?

Dan

[Gary]

With the high superheats, your compressor will run longer and hotter, and the coils will tend to ice up at the inlets. I would lower them. Turning the stems in/out equal turns is as good a way as any, but wait at least 15 minutes after adjustments before you check the temps.

As far as frosting the lower edge of the coil, I wouldn't worry about it, although I would check the condensate drains to make sure they are clear.

Since the unit is working properly, the "on" setting of the pressure control is probably about right. Changing the superheat would probably require changing the "off" setting.

I don't know about other "experts", but I avoid superheat adjustment like the plague. The setting from the factory is usually just right, or at least close enough.

Gary
http://www.gatecom.com/~tmethod/

[dan wong]

Dan, This cold table is approx. 15year old,(working ok for 15 year w/o a timer). medium temp 35F-40F. (I also had two other customers with same type of table, with three evaporators, no defrost timer, Therefore I don't beleive I needed one.) I replace the Txv becuse I thought they maybe bad, I was hoping a pair of BALANCED PORT VALVE would solve the problem.

The two other customer is now with another company, also having similiar problem.

Back to my question, If I disconnect the fans on one evaporator, let it ice up, allow that TXV to shut off, then adjust the other, would that work??? dan wong

[Gary]

Moderator Dan, good point on the defrost timer. Provides a good back-up for the off cycle defrost. I would also recommend it.

Questioner Dan has displayed some minimal training and a thirst for knowledge, as evidenced by his ability to communicate with us, and the simple fact that he is here. I think it safe to say that you and I, at some point in time, were poking our head in where it doesn't belong. The tech in me says go for it.

I would see no particular advantage in alternately freezing the coils, as opposed to just simply setting them one at a time without freezing them. The important thing is to wait at least 15 minutes between adjustments, giving them time to stabilize at the new setting.

Gary
http://www.gatecom.com/~tmethod/

[Dan]

Good point, Gary. I remember the terror when I went in a direction all by myself and wasn't necessarily wrong, but I put myself in that position where I was alone. Can't expect the factory to help once you change components. It gets pure.

I just am not sure what Dan is asking. Is all we are addressing a defrosting problem? Or do we have other considerations that I am missing? What could be the THREE evaporators that he refers to? Front storage, back storage, and top storage? No matter.

In my opinion, going to a balance port valve really makes the job trickier. If others disagree with me, then step in, but I have the opinion that a balance port valve provides wider openings and closings during each stroke, thus changing the operation of the other valves behavior during those changes. It is perhaps the worst valve to have in an undercounter refrigerator because of this.

On the other hand, Dan says that there are other boxes of the same vintage with similar problems. I have to ask Dan: Are the problems simply frosted coils?

The other Dan

[subzero*psia]

To answer your question, yes I think you could.... but not accurately, the valve never totally closes and a frozen coil only means it is running at a very low pressure. Again with two active coils your suction pressure is not going to be totally acurate. One coil could be running at 19 psig while the other is apparently at 4 psig etc. and yet your suction header may be reading only 15 psig for example... (just plugged some numbers in there). So, how would you accurately adjust your superheat on the coil that is not frozen then?

If it has been running okay for 6 months now, why would you want to adjust anything?

You mentioned the bottom of the coil is freezing up... check the drain tube is below the pan bottom. Have you checked the door gaskets and the door hinges to make sure the door is closing properly? Also what is the product going into the cooler and is it above 38 degrees fahrenhiet? Your problem sounds all too familiar to some of my experiences with Chinese restaurants. I have one customer that loads a 0 degree freezer with fresh (38 to 40 degrees) meats... the freezer handles it pretty well most of the time surprisingly.

I have to disagree with you on the level of difficulty... you said there is a liquid reciever, close the king valve and let the system pump down to just above atmospheric pressure then close the suction service valve and shut the condensing unit off. Cut your lines, install your LL solenoids and sight glass(es) then evacuate both circuits. Install your thermostats and wire them to the solenoids, open the suction service valve and the king valve... turn the power on. As each controlled zone calls for cooling the solenoid will energize allowing refrigerant to flow into the evaporator(s) and pressure rises which closes the contacts on the LPC you already have installed. From there you can totally control each circuit individually so you can adjust the superheats.

[Gary]

This is my brother ,Dan...and this is my other brother, Dan...

Sorry...couldn't resist...lol

Gary
http://www.gatecom.com/~tmethod/

[subzero*psia]

Sorry... I couldn't resist that one either! LOL!!

Dan the moderator understands that one but Dan Wong probably doesn't.... Dan you would have to read all the posts on this board over the past couple of months to know.

[dan wong]

subzero, I do not plan to do any adjustment as I've stated ealier, But I still like to know how other "experts" do it.

for moderator dan. The three evaporators I referred to is this: Imagine a long food preparation table, approx 15-16ft long, 6 doors, with three vertical evaporator hanging inside, spaced apart, single liquid line parallel feed each evaporator, and parallel return on suction line with a single suction line back to the compressor. My question is not just a defrost problem in fact not a defrost problem at all, but rather, HOW DO THE EXPERTS ADJUST SUPERHEAT ON MULTI EVAPORATOR SYSTEM?

Gary, You are absolutly right on your comment. Having read that, I wonder If I maybe in the wrong forum. Is there a minium qualification requirement? questioner dan

To avoid future confusion, lets call moderator dan as "WHITE DAN" and me as "WONG DAN" hee hee I can take a joke

[subzero*psia]

How about we just call you Lucky? LuckyDan....

[Dan]

Originally posted by subzero*psia
To answer your question, yes I think you could. One coil could be running at 19 psig while the other is apparently at 4 psig etc.
If it has been running okay for 6 months now, why would you want to adjust anything?

While I agree with your sentiment that there is no reason to adjust something... especially after six months, I fail to see how one coil could be operating at a different suction pressure than another. Are there EPR valves involved?

[Gary]

LuckyDan works just fine for me.

LuckyDan, you are in the right place, there are no minimums that I am aware of, and you have provided an oppotunity for us all to learn and teach. That was just Dan dealing with his evil manufacturer alter ego...lol

Gary
http://www.gatecom.com/~tmethod/

[Dan]

Hi Lucky. There happens to be a wonderful puzzle about what you are asking. Let me see if I can post it for you.

http://www.fridgetech.com/cgi-bin/discus/show.pl?42/124

Enjoy our trade, Dan. I like your name, by the way. It reminds me of somebody.

Dan

[subzero*psia]

[/B][/QUOTE]

While I agree with your sentiment that there is no reason to adjust something... especially after six months, I fail to see how one coil could be operating at a different suction pressure than another. Are there EPR valves involved? [/B][/QUOTE]

Superheat is an indicator of work being done and also of the state of the refrigerant at that particular point. Work increases pressure, no work = a lower pressure in that coil. With more than one circuit, the main suction will have more of an average pressure not to mention that per Lucky's description the service access is located at/near the compressor on this system.

Lucky.... are all these coils cooling the same space or is each one cooling a confined space of its own? Also you mentioned in the beginning that this unit had only two coils and now you are saying there is three over a length of 16 feet of table???

[Gary]

Dean, I would expect that, given a common suction connection, the tendency to equalize pressures would be overwhelming, and that the only measurable difference between the coils would be temperatures.

I have the impression that we are talking about 2 coils in a single space, and that LuckyDan has only mentioned working on similar units with 3 coils in a single space. But I could be wrong.

Gary
http://www.gatecom.com/~tmethod/

[dan wong]

Originally posted by subzero*psia

Lucky.... are all these coils cooling the same space or is each one cooling a confined space of its own? Also you mentioned in the beginning that this unit had only two coils and now you are saying there is three over a length of 16 feet of table???
[/B][/QUOTE]
Originally I had three customers with this brand of equipments. Currently I have only one with the two evaporator setup. The other two customers with three evaporators got a service contract with another company. I still talk to those customers, they tell me they are still having same problem.

The multi-evaporator are hang vertical, air come in on bottom, exit on top, used to cool one large space on bottom, some of these cold air is force feed into the top food rail, where food ingredian are store for easy access. the food load are not evenly distributed. There are no EPR valves, no LL solenoid. It is a very simple set up; liquid line,thru a sight glass come into cabinet, parallel feed each of the evaporator via the TXV, from each evaporator, return to a common suction line back to the compressor. origially, it has a temperture control with thermal bulb in middle back side of cabinet, I've changed it to low pressure control with very wide turn on and turn off, to make sure frost melt before compressor is turn on again. Approx 3" of spacing between edge of cabinet and evaporator housing, not enuff room to install LL solenoid, installing it any place else inside cabinet may violate NSF code,if Local health Inspector turn it down, I would have a lotsa explainning to do, much bigger problem with customer. I know unit will work w/o LL solenoid, because it is now working.

Subzero already answered my question, it is not possible to disconnect fan motor on one evaporator and then adjust SH on the other for reason he cited.

Separate from above, question for Dan moderator, What is C.R.O. stand for. I always call them C.P.R. stand for Crankcase Pressure Regulator.

I appreciated all your comments, I've learned a lot. thank. Luckydan

[Edited by dan wong on 23-04-2001 at 07:48 PM]

[Dan]

That is the Sporlan nomenclature for a CPR valve. Close on Rise of Outlet pressure. Actually, most often you see a CROT valve. The "T" indicates the presence of a Schrader valve... I guess it stands for pressure Tap? The Professor will correct me if I am wrong.

[subzero*psia]

Lucky... I think your customers are going to continue to have this problem and I think some of it is the way they are using the equipment. Try as you will, you cannot solve all the refrigeration problems at an oriental restaurant especially if it is a buffet type. Their equipment gets alot of "heavy usage" and equipment is only replaced or repaired when absolutely necessary it seems. I've walked the road you are on right now Dan... consider yourself LUCKY! LOL!!

~

[Dan]

[i]

To avoid future confusion, lets call moderator dan as "WHITE DAN" and me as "WONG DAN" hee hee I can take a joke
[/B]

Hahaha! Somehow I missed that, Wong Dan.

White Dan

[Prof Sporlan]

<i>That is the Sporlan nomenclature for a CPR valve. Close on Rise of Outlet pressure. Actually, most often you see a CROT valve.</i>

The Prof thinks Dan is ready to be a Sporlan Product Manager....

<b>CPR</b> is a generic acronym for the crankcase pressure regulator. The same is true for an <b>EPR</b>: evaporator pressure regulator. Sporlan has historically used the function of the valve as its model type: a CPR Closes on Rise of Outlet pressure <b>CRO</b>, and an EPR Opens on Rise of Inlet pressure <b>ORI</b>. Alco has used a similar approach <b>IPR</b> for Inlet Pressure Regulator, their direct acting EPR, and <b>OPR</b> for Outlet Pressure Regulator, their direct acting CPR. The Prof, of course, finds the Sporlan nomenclature superior.....

[Prof Sporlan]

Of course, someone might wonder why Sporlan didn't call thir CPR valve an <b>O</b>pen on <b>D</b>ecrease of <b>O</b>utlet presssure <b>ODO</b> valve instead of a <b>C</b>lose on <b>R</b>ise of <b>O</b>utlet <b>CRO</b> valve. Calling it an <b>ODO</b> valve would have no doubt amused some Star Trek/Deep Space Nine fans.


[Edited by Prof Sporlan on 24-04-2001 at 03:17 AM]

[Gary]

But it would keep changing it's shape.

[subzero*psia]

Did I miss something Gary? What would keep changing shape?

[Gary]

Yes, Dean. You missed numerous episodes of StarTrek/DS9.

[subzero*psia]

I used to be a Treky! I watched DS9 too... not the same as Star Trek though...

[Gary]

My kinda guy...these days it's "BattleBots" and "Junkyard Wars"

[subzero*psia]

No slamming of Junkyard Wars!! LOL!! You never know... one of the episodes may show a primative Warp Drive system...

LOL!!!

[Prof Sporlan]

The Prof has a bad habit of making obscure remarks , though he senses a number of science fiction fans in this group. <b>ODO</b> would make an interesting name for a valve, say one that could change its capacity, if Paramount Pictures not claim royalties to it..

[subzero*psia]

I posted something earlier in this thread that wasn't correct and Gary caught it. I knew what I was thinking but for some reason I went off the deep end with the wrong explanation.

If the TXV's are not closely balanced, in a parallel system they will fight for control. Of course the one with the lowest s.h. will ultimately control both circuits. That is why solenoid valves are needed. Now I think I have stated it correctly this time. Thanks Gary.

[bernie]

well ill just dive in! Ive read all of the threads on this subject. It seems to me that the run times for this box are going to be long. most times a pressure controllers off cycle will be to short to control ice. I would think this would be true in your case(90-95 degree surrounding box temp). Id be against adding LL solenoid valve due to the increased load it will put on the compressor with one closed. We will possibly have some major liquid slugging.
Anyway, if all else fails get a bigger hammer

[subzero*psia]

Hey thats no joke... I have seen locked up compressors that just needed alittle LOVE TAP to get them going again! LOL!!

[dan wong]

Subzero, with due respect, I beleived Bernie is right. solenoid maybe good for adjusting SH. but present a bigger problem down the line.

My way of thinking, even if the TXV is not exactly adj - but reasonablly close to each other, one evaporator will carry a slighly bigger load. I can not see how one TXV can eventually over power the other. Unless the other one is none functional.
Bear in mind, both evaporator is cooling the same space, same temperture.

[bernie]

hey dan consider this. Its not uncommon for folks to use one side of the box frequently i.e. opening and closing the door all day long. If it were me id probably due that design change thing and jam a remote bulb thermostat in the evaporator that always freezes and set to cycle off at say 18 degrees and back on again at 41. this should cure the ice problem somewhat. good luck