MV600 head pressure trip (ghost)

okay so the other thread that i submitted was put in the wrong place, you can see that i am new here.

Hi all
maybe somebody can help on the problem that I am baffled by here, installed a new scotsman MV600 20 december 2005, unit ran perfectly till just after new year then started tripping on the head pressure controller, we checked the unit and left it to run , unit ran perfectly in temperatures of 35C/95F with no trips, unit then started tripping sporadically last week, only over night, we ducted the hot air out of the room and checked head pressure,replaced the condenser fan motor, the head pressure is never over 350Psi , unit ran again for two days then tripping started to re-occur, double checked head pressure, air flow over condenser, unit still tripping over night, I contacted the Head Technician for SA for possible solutions.
The unit was taken off automatic control to manual control on jumper switches (PCB) unit ran from friday mid day to sunday night then tripped again.
The unit runs perfectly during hot and cool days, but as soon as it starts to rain , or fairly heavy rain has fallen the unit trips out on the head pressure switch.
If anybody has heard of this problem or has any suggestions please let me know, it has most of us in town baffled

howzit boet
ok in reply the head pressure switch is one of the new fangled sealed units, most probably made by ranco has a set cut out, usually it is found at the back of the unit so that the customer cannot reach it, standard push button type
as for the pumping liquid on start up , hadn't thought of that one , the unit has a weighed in charge of R404a, so it is critical, have no freezing back to the compressor at all, have tried to simulate a very cold day by spraying water in the condenser, but the machine just carries on as normal fan cycles correctly, that is why we cut it from auto to manual, thought pattern was intermittent fan motor or condenser sensor . the weird thing is the rain, it only trips with rain, could the earth be stuffing it around ?

Andre, is the unit in use during the night or more correctly are there staff around at night ?

When it rains does someone throw their raincoat over the unit to dry it off?

It is not unheard of for those sealed pressure switches to go faulty; how about installing a pressure switch that you are familar with to replace the existing.

One other thought - why not swap the thing under warranty ?

Is it definitely the pressure switch and not the condenser temperature sensor that is tripping?

Hope you solve it. I assume that you have a manual, not that they always help but.... http://www.scotsman-ice.it/docs/manualsIng.asp?id=25 if you want one.

Hi brian
the unit runs 24/7, at a golf club staff are there until 8 at night and up until then the machine has been running, when it hasn't rained, the unit is underneath an awning, type of concrete roof, so it least it is dry.
reason why we have not cut out the excisting HP control is i am not entirely satisfied that it is that , could be so will fit a secoundry unit on the service valve and re-wire in the morning.
swapping it out , lets just say that the customer is rather peeved off, they still owe ZAR4000.00 on the installation and they are not paying till it is sorted out seem to think that it is enviromental, the electrician is an old guy who doesn't believe that it is his fault, but they are having interrupted power problems, ie. blackouts for 0.5 second have asked the town engineer for a voltage recorder to test the electrical installation, that maybe installed in the morning.
the condenser temp sensor can be switched off by forcing the unit into manual mode , and running the fan continually, not a bright thing to do in winter but we still got hot weather here for 3 months so what the hell, we tried that on friday but it tripped on sunday night. tested it again the whole afternoon, and it is running great , produces every 19 minutes, which is dead on
I dunno anymore

thanks for the link to the manuals in there now lifting it off

thanks marc will spend the day in there , but it s 2:00 am and i am off to dream of scotsmans will let you know the outcome in the morning

hi marc
the unit had tripped overnight, but this time no rain, so my theory was blown out the water, ran the unit with water on and off the condenser to check the fan cycle switch which happens to be a triac on the PCB with a flimsy heat sinc, watched the unit for 3 hrs and no trips, the condenser probe is working correctly, that i do know, checked the unit late this afternoonfor roughly 2 hrs, fitted a amp meter to the fan motor as well as a multi meter, unit cycles the fan correctly, however did pick up some thing, about an hour after watching the unit the amps sprang from 1.1 to well over 10, this happened for a very short time and never happened again, does any one have an answer for this? we have earthed the unit to the main water supply pipe (yeah we still got copper pipes), as well as put a data recorder on to the mains supply to check for any spikes in the power, that happens very often down here, we got the dirtiest power as well as the most expensive.
silly questions if anybody has electronic experience, what happens to a triac when it starts to overheat?
any answers please let me know

Thanks Marc
that explained great even for this dislexyc, explains the fault of tripping early evening,hypothetically "if the unit was working non-stop from 10am the triac would be cooking, start 'breaking down' and the unit would be tripping early evening, the biggest thing that struck me this morning when i opened up the machine was the PCB was a lot cooler, to test this "new theory" I will fit the fan motor directly to the compressor's contactor and watch it till monday, will check it out and let you know,
thanks for all the help

Hi andre,

I built an ice-machine and I had a problem when I was testing it like you said. May be it is worth checking.

When the machine goes to defrost cycle then, if for any reason it stays there then you will have Hi pressure cut out. I had this twice and once the compressor was overheated and tripped. This happened for me because I removed the ice mould cover which actuates the micro switch. Then the machine stayed on defrost cycle for more than necessary?:D

I hope this helps.
Cheers.:)

Hi:)
did you try changing the condenser fan and its starting electrics:confused:

Kind Regards, Andy:)