Display Fridge Tripping HP Switch

[jammy23]

Hi, I was asked to go and have a quick look at a beer display fridge yesterday evening, it is a J&E Hall condensing unit....unfortunately I don't have the model to hand. The data plate says R404a but at some point the compressor looks like it has been swapped out for a R134a compressor....which I know J&E Hall have units which you can choose which gas it runs so unsure if this is what the original compressor was or if the original was a r404a one. I checked to make sure the expansion valve was r134a and it is.

The paper work the last engineer left said he re-gassed the unit with R134a and put 4.3kg in, the sight glass is flashing through and for some reason it is tripping the HP switch even though it is set at 250psi. I couldn't tell you what the running pressures are on the high side as there is only one service point on the system and that is on the suction right before it goes into the compressor (not a rotor lock valve).

The discharge air from the condensing unit doesn't feel warm at all, the compressor seems to be running warmer than you would probably expect but not boiling....I suspected that there may be possibly air in the system and this is why the symptoms are like this? I have never come across this before so abit bemused by it...according to the guys paperwork all he has done is pressure test the system with nitrogen, repair a leak on a rotor lock valve on the receiver and re-gas!? I have also checked the condenser coil and it is clear, but I know from previous jobs even if it was blocked you would feel the excess heat and there doesn't seem to be much.

From what the customer told me the unit seemed to get down to temperature ok when it was first done but after a few days began not working. Anyone ever come across anything like this before...I have to go back Monday to try resolve the problem, so just wondering if I was going down the right track by reclaiming and recharging?

Thanks

[chillerman2006]

ok so you had a look, a touch and a feel

What are the pressures and temps

Subcooling & superheat

[Kenneth199]

Is there a solenoid valve on the system? Nitrogen could be trapped in the HP side while vacuuming LP side only.
I would reclaim the refrigerant, weight it. Put in a service point at HP side. Pressure test.
Or it could be the fan that suddenly cuts out, thermistor relay or something.

[cadwaladr]

if it was on 404a at some point then the hp switch would have a higher cut out than 250 so if the comp was changed along with the txv the switch must also have been changed is there no fitting access point on the high side anywhere.

[charlie patt]

Is it on fan speed control? And they have gassed it without locking out fan thus its overcharged or it's got non condenseables in it one or other carry out a pump down test and check

[jammy23]

To be honest, the whole thing looked as though it had been tampered with but as is always the case the customer can never tell you what work has been done. The fan speed controller and hp switch are both tapped onto the receiver service valve and so that leaves no other service points other than the suction on the compressor.

where the liquid and suction pipes connect to the condenser, they have been braised in....I have seen this before but usually service schrader valves are added so you can get access to both sides of the system, but not in this case.

The thing that made me think it was air/Nitrogen is I read somewhere that this can cause low condenser temperatures as it can get locked in there and prevents proper heat exchange....also the condenser fan looks to be running flat out suggesting there is high pressure causing it but again there is next to no heat from the condenser. As far as running pressures, obviously because I could only get the suction, these were coming back at about 43psi.

I think I will do as suggested above and reclaim the lot and weigh what comes out, add a service point on the high side of the system so access can be made and see exactly what is going on. At least this way it can be eliminated as the problem and gives a better base to work from I suppose.

Thanks for all the responses, ill report back if it solves the issue!

[Rob White]

.

The service valve on the receiver can be used to measure running
pressures and it would be a good place to test for Nitrogen.

Fit your gauges to the system on both sides and do a standing pressure
test, measure it against the ambient temperature and see if there is a difference.

If there is a valve on the receiver you will be able to fit your gauges.

All the best

Rob

.

[monkey spanners]

Has the fan speed control be reset or replaced to suit the lower running pressures of R134a versus R404A?

[al]

Fit a tee piece on the receiver and do as Rob suggests, without pressures/temps you're pi##ing in the wind. You may need to pull charge, vac and recharge. when you have charge out check the bottle pressure to see if nitro is in there.

[cadwaladr]

If you don't know exactly by a gauge how can you be sure the h/p is tripping at the correct pressure and if this system has been vacced correctly without access to the high side

[mikeref]

43 PSI Suction on R134a will carry significant heat through to the Condenser, unless Compressor valves are damaged. Run a pump down.
Check compressor Amps at 43 Psi and compare that to it's run load amps.

[jammy23]

Just wanted to update on the state of the unit. I reclaimed the total charge and it was slightly over what he had noted he weighed in, I added a T to the receiver so there would be a spare point for gauges for future. Regassed and ran...noticed a massive difference, plenty of heat from condenser...fan was ticking over nicely rather than running it's nuts off like before. High side was sat steady at just under 150psi...brought temperature down nicely and never tripped HP switch, so looks like there must've been air or nitrogen still in there.

Thanks for all the tips! Much appreciated!

[Kenneth199]

The system might have been overcharged. The discharge gas would not have any place to condensate in the condenser, because there is too much liquid in condenser. Therefore you would get a higher pressure than normal.
That could also be the problem.

Found a link that describe overcharged:
http://www.achrnews.com/articles/91093-the-symptoms-of-refrigerant-overcharge

[jammy23]

I don't think it was over charged, the difference was only about 150 grams. It makes more sense that it was either air or nitrogen, especially with the fact there was originally only one service point so can have only been vacced from one side of the system making it very likely part of the system was missed. Good link though and definitely worth the read for future reference!

[Rob White]

.

Thanks for the follow-up post, good to hear you have sorted it.

Regards

Rob

.

[pie man]

Becoming very popular these J&E Hall units on cellar coolers/cold rooms etc. Have found the same problem with only access to the low side. Also, have had x3 go down with gas leaks on the hp Schrader Stubbs splitting. Seems like a design flaw so something to watch out for!