low temp freezer-20celsius

[jamcool]

Guys,
have a low temp 4 door fridgidaire on 404a working fine no complaints,put gauges on system while running,low side reads 6 psig high side 350 psig and needle on high side is vibrating like crazy ,shut unit off it does not equalize,comp is semi-hermetic copeland have not taken any superheat or subcooling readings no contact thermometer the condenser coil seems clean,used a flash light it shines through ,found out that there was a leak another tech. fixed, charge by data sheet changed drier,my question y the mad vibrating of the needle? suspect a comp. going bad,pumped unit down went into vaccum in no time vaccum help high side reading stayed the same no leaking.Ambient is between 75-80F.(23-26c)
Dont want to say"if its broke dont touch it" but the high side bothers me,it just is going crazy any advice would be good,my gauge set is working have used it on other units since.short of taking out charge and recharging with new drier where else can i go?

[Dan]

Not sure that your vibrating high side is a problem or not. Your condensing pressure is high, as it is 125 deg F. First thing that comes to mind is an overcharge or noncondensibles. What is the temperature of the refrigerant leaving the condenser?

short of taking out charge and recharging with new drier where else can i go?

Home?

[Andy W]

Old fashined gauges used to vibrate like mad, all we had to do was slightly crack off the service port to reduce the vibration of the gauge, now adays most decent gauges are equipped to deal with needle flutter. The head pressure bothers me, If there has been a leak and it has been topped up the "blend" may be incorrect, I would vac it out and put a fresh charge in it.

[jamcool]

Will be doing some more checks on this unit,its like pulling teeth have also learnt,after asking that there was also a fan motor change when the leak was fixed,no answer as to y but also wonder if the "new" motors rpm is the same as the old,there is nothing like going to a unit after someone or some2 has gone to it no one is talking and u have to figure out what they have done and then do your thing,and this wasnt even a call out just had some time to kill and said let me put my gauges on the unit its good experience but at times is drives me up the wall this unit is so basic its not real,they store ice cream in it, it has no pressure switches,not even a sight glass(neither oil or liquid) the only protection is a thermistor in the comp. windings and the regular klixon on your comp. body,which is working so i figure it may be cutting out on high temp on the body every now and again,but the cream is not melting so they are not bothered.
Nearly had my head taken off when i told them i wanted to take the unit out of service because i had concerns,its out but no ends of cursing by the users,just have to grin and bear it ,these units have become my responceability so at the end of the day its not the others that have visited it will get the blame.
A long story but had to share.Will take my thermometer with me and take some temp readings.
Thanks so far guys and keep the thoughts coming

[frank]

there was also a fan motor change

Has the motor direction changed? Is air flow across the coil OK?

[old gas bottle]

the pressures are all wrong i think, has it got the right expansion valve in it, i would slip a new drier and sight glass in, recover the charge and liquid charge it agian,sounds like a restriction or bad refrigerant,ie too much/wrong one/mix ect.

[Brian_UK]

Regarding the vibrating needle - is the pressure connection close to the compressor ?

Sometimes the pulse from the discharge valves can affect gauges if they are too close.

[jinxycat]

hey, hows it going, that head is very high even for 404a, also its evaperating at like -39 deg c sounds like a restriction as anything on the high side thats a problem would hold the suction up to, is it cap or tx?

[Pickles]

Does the noise occur instantly upon compressor startup? or is it delayed?

it may be possible that when the leak was repaired the system wasnt evacuated properly leaving behind a high moisture content. When the system starts running it may cause moisture to freeze internally in the tx body ,this would result in the high dsch pressure and low suction. Try carefully applying some heat to the valve body whilst sytem is operating then monitor you system pressures to see if there is a change.

[jamcool]

Thanks for all the reply,guys,the truth be told,was so pi.. at the whole situation that was hoping that i did not have to do much work on the unit,but after couple pints got down to work,even changed the oil and added dual pressure switches,found a manual for the unit and also found that the rpm on the condenser motor was alot higher than the one my friend had used,so got the correct motor,the last tech. on the unit also told me, after alot of threats all he had done onor not done on the unit,including charging 404a to unit as a vapour.
So alls well that ends well and the unit is ok .
Final word this is a GREAT forum keep up the good work moderators,and all members keep on keeping on
EASY NUH!!!!!!!jamaican style

[Langer]

Good to see you sorted out the problem.
If you have a problem like that again (gas leak)
It would be worth your while changing your refrigeration charge, give it a good vacuum and recharge in liquid state.

The low-pressure switch might have been set too low, thus sucking air into the system. Air causes high head pressure
And low back pressure.