Frascold A17Y compressor rattling

[sminett7]

Hi All,

I have been working on a display fridge with a Frascold A17Y compressor on it, it is running on R404a, I have changed all of the components e.g. compressor capacitors drier expansion valve and orifice. After vacuuming the system out (3 torr) start adding the refrigerant in to the liquid receiver. I start the system up it runs ok running at 2 Bar but when I add some more refrigerant the compressor rattles like mad then the starting relay sparks and the unit trips out. When the compressor is running at low pressure i.e 1.5 - 2 Bar it runs ok but cant get my head around why is rattles the trips out when I add more refrigerant.

I would be grateful for any help you guys can give.

[monkey spanners]

Are you sure its rattling and not cycling quickly on a pressure switch?

What was the original fault?

[sminett7]

Yer it's deff rattling after the pressure gets up to just over 2 bar. The original problem was the compressor pistons seized. So I replaced the compressor with a re conditioned compressor and the capacitors and drier. Then after I commissioned the system up to a pressure of 2 bar suction and 17bar discharge pressure the compressor was rattling as if it was struggling to compress then it chugs and trips out. I then changed the expansion valve with No 3 orifice and blew out all the pipes with nightrogen because I thought it might be liquid coming back but after all the parts change it still does the same. Could it be a faulty re conditioned compressor,

Thanks for the reply

[cadwaladr]

Did you change the potential ,starting relay,in fact all the electrics it's good practise if the original failed find out why it did before switching on the replacement!

[monkey spanners]

Suction superheat will tell you if its liquid returning, maybe you are seeing what killed the original compressor?

Is the evaporator clean and all fans running the correct direction, good airflow? Ofter shop fridges the grills and air holes get blocked with dust and lint.

[cadwaladr]

most compressor rebuilders insist you change the txv,common knowledge to change all the electrics and change/clean all filters in system,as said before something killed the old one and you need to find out what pretty darn quick me thinks

[Pete.Sigs]

Hi All,

I have been working on a display fridge with a Frascold A17Y compressor on it, it is running on R404a, I have changed all of the components e.g. compressor capacitors drier expansion valve and orifice. After vacuuming the system out (3 torr) start adding the refrigerant in to the liquid receiver. I start the system up it runs ok running at 2 Bar but when I add some more refrigerant the compressor rattles like mad then the starting relay sparks and the unit trips out. When the compressor is running at low pressure i.e 1.5 - 2 Bar it runs ok but cant get my head around why is rattles the trips out when I add more refrigerant.

I would be grateful for any help you guys can give.

May I suggest at this juncture that you record the sound of the run condition and use it as a novelty ring tone
for all junior engineers that may want some thing for a PJ

[Glenn Moore]

Hi
The Frascold compressor is a Low Back Pressure machine and can only work from minus 5 degrees or below evaporating. Which means the motor in the compressor is sized so that if the compressor suction condition goes any where above minus 5 on the suction guage the motor operates in an overloaded condition. This overloaded condition causes the start relay to pull the start winding back into circuit which makes the compressor shake rattle and roll, and the relay starts to arc and spark You will then burn the compressors start winding making it useless.
You should have an MOP type expansion valve or a crankcase limit valve fitted so that the compressors suction pressure is never allowed to rise above the motor limit value. If you fit an MOP expansion valve such as a Danfoss T2 with NL MOP range then the suction at the compressor will be limited to minus 10 degC and below thereby preventing the compressor motor being overloaded. If you fit a Crankcase limit Valve such as a Danfoss KVL valve into the suction line you can adjust the crankcase pressure via the KVL valve to a suitable pressure at the compressors suction that the motor can cope with.
THis maybe why the original compressor failed. If a standard range of expansion valve was fitted by mistake, to this system the motor would always run in an overloaded condition until the evaporating temp / pressure dropped to a level that the compressor was designed to work.
I am a little puzzled as you say this compressor is fitted to a display fridge but his model of compressor is designed to work in a Freezer application ie Low suction evaporating minus 10 Deg C or below Br Glenn