View Full Version : Correct Super Heat For Walk In Freezer

18-02-2017, 02:22 PM
Hi, had a service call to a J&E Hall Fusion 0300-b2-m-3 Condensing unit for a walk in freezer running on R404a at a set temperature of -20 Degrees C. The unit seems to be getting to around -13/-14 Degrees C and sitting at that, the suction pressures are at around 20psi and Discharge is up and down between around 160-180 (fluctuating with fan speed). I took temperature readings at the suction valve which were at -9 Degrees C and at the expansion valve bulb which were -15 degrees, am i correct in thinking this is quite a large drop considering everything is well insulated? My first thoughts were that the suction was a tad low and discharge a tad high and perhaps the expansion valve needs adjusting. In the manual is says superheat 10k and sub cooling 0k. With the unit being set at -20 does this mean the return at the Evaporator should be coming back at -10 Degrees C and so the valve needs adjusting to allow more refrigerant through? The system runs with a full sight glass and seems to function correctly apart from stalling at -13/-14, apologies if this seems like a dumb question as this is not something i have encountered before or the type of unit i usually work on (mainly air con)

Thanks in advance.

18-02-2017, 02:58 PM
Always work in temperatures not simply pressures.

Assuming that your 20psi is measured at the compressor suction valve as was your -9C then you are running at 35K compressor superheat, which is rather high.

18-02-2017, 03:10 PM
The 20 psi was taken from the service suction which is the closest point to the compressor and the -9 was also taken from the pipework at the same point.

18-02-2017, 08:56 PM
Had a thought earlier today, could the unit still be under charged? i was told it was swapped in late December so outside air temp would be low, would the condenser fan need to be running high when charging as i know you have to do this with some cellar coolers to ensure correct charge. I am just wondering if that's whats required and whoever installed didn't do this. I found a manual online but there is no mention to do this but i know when i've been to it, it doesn't run at full speed (likely due to low air temp)....would turning the fan speed up and charging to a full sight glass (if required) create the potential for over charging?

18-02-2017, 10:18 PM
The first thing to confirm would be airflow. Is the coil clean and are all fans running and going in the correct direction?

With a 20psi/-26SST and an evap exit temp of -15'C your evaporator superheat is 11'K.
Did you take the sub cooling temperatures? Amp draw or air off temperatures? These would help to diagnose the problem further.

Regarding the head pressure, it's too low, try adjusting the fan speed controller to at least 210 psi to get
the head pressure up.

18-02-2017, 10:35 PM
Air flow both indoor and out is good, indoor coil is spotless and the outdoor unit is brand new so again spotless. i took the temp just after the service valve, roughly same spot as the suction and was fluctuating between 20 degrees C and 22 (again with fan speed) with pressures of between 160 and 180. The condenser fan seems to be running slowly for the most part then speeds up to get pressures down then slows down again. I suspect if i was to speed the fan up so it was running faster the sight glass would probably flash as every now and again it does. As soon as i get set up to add anything it clears and stays clear (very annoying) as i don't deal with walk in freezers very often i am reluctant to just bang gas in, especially if it is a brand new unit. On a unit like this is 210 roughly what youd be looking at head pressure wise? if so i could set the fan speed to that and see what the sight glass does, if it flashes charge it til full and see how that goes on?

18-02-2017, 10:55 PM
Ideally you want to get the head pressure up to around 38'C SCT which on R404a is about 240psi.
I'd say 210psi would be the minimum you would be looking for when the systems running.

Don't forget the pressure differential across the TEV port affects the rate of refrigerant flow, low head pressure generally causes insufficient refrigerant to be fed to the evaporator.

I wouldn't be adding any more gas just yet, not until you've increased the head pressure and checked the system pressures and temps again, including the subcooling. Remember a sight glass is only an indication on charge, sub cooling is a much more accurate method of checking a system charge.

19-02-2017, 08:11 PM
So i went back today to take another look at this freezer and turn up head pressures etc, turned fan speed down and had head pressures at 210-240psi and left to run at that for a while with little to no change. upped the pressures to 230-260 (36-41C) and checked subcooling, pipe temp after service valve was up and down around 28-29C. I reclaimed a bit of gas and got this up to 30-31C on the pipe running at the same pressures. Room temperature didn't budge much though so checked super heat and managed to get it coming back down suction at -16C by adjusting expansion valve with suction pressures of 20psi (-26C) but still couldn't seem to get it below about -16.5C room temp. I forgot to mention that on Friday i noticed the pipework is different sizes to the unit sizes. The unit is 3/4, 3/8 and the pipework between the units is 1inch1/8 and 1/2 liquid. I spoke to the technical guy at my suppliers and he said it should be fine with that piping so eliminated that from the equation, could this be causing the issue with temps not coming down? Probably should have rung J&E Hall regarding this and get their take on it. What sort of Super heat and subcooling readings should i be looking at getting as there is no manual for it and all i can find online says rating 10k superheat and 0k subcooling but i pressumed this was what they got there technical data at when testing. I am going to speak to J&E Hall tomorrow regarding this, ive spent so much time trying different things to get it to come down ive blagged my own head :p

19-02-2017, 08:25 PM
What are the defrost intervals and defrost termination temperature,could it be simply defrosting too often or terminating at too high a temperature,is the insulation good and doors seals sealing correctly and what is the fan start and stop parameters set for.

19-02-2017, 08:33 PM
I know the door doesn't seal great at the bottom as there is a small dent in the floor for air to get in, rest seals well though and apparently his old unit still worked to -20C as the door is now. Doesn't defrost too often or for that long but clears everything when it does so no ice building up, coil is clear and airflow is good. I think the defrosts are every 8 hours and for around 5 mins a time which when you watch it defrost is plenty. Drain heater works fine and is insulated so no massive extra heat gain from that when defrosting.

19-02-2017, 08:45 PM
Very frustrating reading this post. I tend to never adjust an expansion valve, as once set at first commissioning it should never ever need adjusting. It will either need replacing or more importantly there is usually something else wrong within the system. I agree with Marc5180. Discharge pressure does seem low.

It could be a number of small issues resulting in your problem. And remember, as hard as it is, best to leave a system 12 - 24 hours after an adjustment to allow it to settle and balance.

Don't think I've helped much!!

19-02-2017, 08:51 PM
In all honesty neither do i, it was the only thing i could think to try and bring the temp down. From what i have been told everything other than the condensing unit is the same as it was when the old condensing unit was piped in but for some reason this unit doesn't seem to want to come down. either that or i am over looking something.

19-02-2017, 08:54 PM
It does seem to be a frustrating call,is the new unit the same capacity as the old one in duty,yes I like to see 404a at 250 psi maybe slightly higher then the fan speeding up to drop it down again has the filter drier been changed recently ( I always write the date changed on the kit I work on ) check that duty out against New and old,somethings weird if it reached set point with the old kit?

19-02-2017, 09:54 PM
In all honesty i don't usually mess with the expansion valves on units but this is the only time i could think it may help with the temperatures. I guess im going to have to try if manufacturers can shed any light on what could be causing it.

19-02-2017, 10:26 PM
Yes, as previously mentioned, playing with the expansion valve is never going to make a system work especially if something else has been changed. In this case the condensing unit.

If the valve worked before why should it not be working now? If it has stopped working properly then it needs changing.

19-02-2017, 10:35 PM
Just reading back through the comments to try and figure this out...originally the unit was running between about 160-180 psi head pressure and was later turned up by myself to 210-240, then to 230-260. If the unit was charged with the condenser fan holding the pressures at 160-180 is there a chance that the unit could have been over charged for the higher running pressures? If so, could i not just remove some of the charge via the liquid side until the sight glass flashes again and then top up until it stays clear? then the charge would be correct for the higher running pressures? Maybe i am clutching at straws now but it is really irritating and i know it will end up being something pretty simple. lol

19-02-2017, 10:49 PM
Did you take an air off temperature?

My first thought would be defrost frequency or airflow/evaporator fans.
Did you make sure that all of the fans are spinning the correct way and that all of them are working properly. Sometimes one of the fans can fail but it looks like it's running because the other 2/3 are causing it to spin.

Rather than adjusting the expansion valve, hold the TEV bulb in your hand and see if the valve opens and the superheat drops, this should flood the coil but be careful because this will cause liquid flood back to the compressor but it's a way to check if the expansion valve is working.

Another thing to think about would be the refrigerant, especially since it's had some removed and recharged. I'd be slightly concerned about fractionation (separation) of the refrigerant so I'd probably want to give the system a good vac and recharge with virgin R404a, just to eliminate that.

19-02-2017, 11:26 PM
The point about the refrigerant is valid,although in truth if you do not recharge it from scratch you will never know it's consistency so that would definitely be my next move I just hope your customer rewards you well for all the issues you are trying to solve!

19-02-2017, 11:55 PM
With respect to the sight glass remember that the system is only operating in a stable mode when the space is down to design temperature.

I bet you're glad that you got this job given to you. ;)

20-02-2017, 12:02 AM
Mmm.....just Googled that Condensing unit, and that model is only rated to -20C on 404a, giving 3,4kw. And is stated at that as a MEDIUM TEMP condensing unit. That model does not appear in the LOW TEMP section of the J and E Brochure...sorry, can't seem to attach brochure I found.

here is info from Emerson website


Whats the Evap model and size of room?

20-02-2017, 12:56 AM
Aha,somebody once again confuses duty with horsepower that's the logical answer,whoops who picks up the invoice?

20-02-2017, 01:13 AM
Hi Jammy
A few questions which might help us solve your problem.
How far is the evap from the compressor?
Is there an access point on the suction line at the evap?
Is there frost at the compressor?
Is there a suction accumulator?
Is the TX bulb secure and in the right position on the suction line?

20-02-2017, 01:35 AM
Sitting on the fence here,but the call to j+e hall regarding the duty should provide results I have no faith in wholesalers of equipment they use guess work in my opinion well at least some do and leave the fridge tech high and dry for slaughter,better to over compensate in my opinion the days of honest wholesalers has gone they just want a sale with no comebacks but you can sue them quite easily for losses,always make sure you give the correct load requirements both in email and letter so they can not argue phone calls don't stand up in court I am about to start legal action which will if I win shut a rogue wholesaler down,they supplied equipment that yes would do the requirements unfortunately did not and put lives at risk,my public liability company has started the proceedings on my behalf!

20-02-2017, 05:42 AM
One more question.
You say that this was installed in December. Has this had problems since then or has it been holding the freezer at -20'C since it was installed and the problems have only just started?

20-02-2017, 06:28 AM
Hi Guys!
Is it just me?
Only I cannot get past this fact stated that the subcooling should be 0k.
Without sufficient subcooling how is the system supposed to work?
I check the charge by reading the subcooling.
Not the superheat.
Just the ramblings of an old Man!

But I am confused by this post.
When did we start reading superheat at the compressor suction?

20-02-2017, 06:50 AM
We didn't,but this guy admits he is more at home with a/c and maybe out of his comfort zone,where is the person who installed it has he rode off into the sunset with bulging pockets? I would have walked away myself and told the customer to get him back I can only see problems getting paid with this one

20-02-2017, 07:01 AM
I checked the design data and it does confirm 0K, it must be a typo, surely.

From the OPs posts, it looks like he's getting 10K subcooling (a little high) not the 0'K the manufacturers ask for.
I think speaking with the manufacturers to confirm the things like pipe sizes and duty of the unit should be the next step.

20-02-2017, 05:04 PM
Wise Words Cad and Mark.

Maybe I was being Harsh.

20-02-2017, 05:45 PM
You know what they say good advice is best given away!

20-02-2017, 08:25 PM
Still gotta fix doors seals etc no matter what!

20-02-2017, 11:40 PM
True any heat gain needs to be rectified asap

25-02-2017, 09:56 AM
Hi all, really sorry for the late update this is the first time ive managed to get to my laptop. Just to answer some of the comments further up, YES this has been like this since just before Christmas. By the sounds of things the guys have fit the unit and not tested properly before leaving and when asked to come back, make excuses even though they had already been paid for the work (which is probably why). The unit was off for the Christmas period and part of January apparently as it wasn't required and was run up and found all these issues.

Believe me i felt like walking away from this one but didn't want to be another engineer thats left him in the s**t and on the plus side have actually learned a few things from this job. I rung the manufacturer on Monday morning and they basically told me they couldn't offer me any advise as these units are used for so many different applications. So ended up speaking to technical at wholesalers again and after looking into the unit in more detail, turns out it should be a number 4 orifice in the expansion valve and this had a number 5. On swapping the old one out i noticed it was pretty dirty so no doubt causing some flow issues too. After swapping and vaccing i ran the unit up again and it seemed to run completely differently and more like i would have expected first time around. Pressures were higher for longer and dropped with temp and compressor seemed to be running a lot smoother, topped up the gas charge and watched it down to -17 before leaving site as it was quite late and quite a lot of stock in. Came in next morning and was down at -19, but i suspect it had already reached temperature. The only issues left were the pressure switches hadn't even been set up so wasn't pumping down properly on defrost and final temp. I kept tabs on how it has been over the last few days and has been regularly down at -20. The suction pressures were between 13-14 psi which i thought was a tad low but was assured by the technical guy at the wholesales this was fine for this unit.

As far as door gaskets go, the gasket is in really good condition but there is a dent in the floor plate which leaves a small gap under the door. i have told the guy about this and that it will allow heat in, i think it is something he is going to do but may be a fairly big job as i think he will need to concrete under that area to stop it doing it again. I think it has happened over time when pushing trollies of meat in to the freezer, just through shear weight and repetitiveness.

Thanks for all the advice guys, really appreciated and sorry again for not getting back with an update sooner.

25-02-2017, 10:18 AM
Glad you got this sorted.

Thanks for updating the thread.

25-02-2017, 04:18 PM
As Marc said, thanks for the update. It's always good to hear of a positive result, well done.

25-02-2017, 09:45 PM
Wonder what superheat ended up at?

Guner Edip Riza
26-02-2017, 01:54 PM
Considering the fact the there is not much difference between no 4 orifice 6TR and no 5 orifice 7.7TR and there was no hunting mentioned.
What was the real issue?
Size of the orifice of the expansion valve or dirty/clogged expansion valve orifice?
Your ideas/conclusions will be appreciated.

26-02-2017, 02:05 PM
Considering the fact the there is not much difference between no 4 orifice 6TR and no 5 orifice 7.7TR and there was no hunting mentioned.I think that there is a difference between 6TR and 7.7TR namely 1.7TR or +28% which is why they make different sizes.