possible??

[sean1]

hi,
is it possible to have the right suction pressure but have excessive high superheat - enough to cause the compressor to overheat?

[coolhibby1875]

wouldn't have thought so

[Brian_UK]

Who is to say what the right suction pressure is ?

[monkey spanners]

If you have high suction superheat the evap is being underfed with refrigerant or the system is picking up too much heat in the suction line.
Its all about the temperatures, not so much the pressures, pressures only make sense when converted into temperature in a working system, its what the are designed to do, change the temperature in an enviroment.

Give us some more info, system type, refrigerant, air on and air offs, pressures, superheats, subcooling and some of the clever people on here (not me ) will be able to tell you whats going on and where it going wrong.

[sean1]

thanks
not got alot but goin back tommorrow but heres what i have.
cellar cooling evaportating at +5c onr407c
temp at bulb for tev 22c room temp 22c
evap coil only cooling at distributor,air on 22c air off 21c
unit runs for 5 min then cuts out on overload , compressor hot cant touch it
the compressor has just been changed and the customer informs me he has had at least 3 compressors in as many years
just want a few ideas when i go back

[mad fridgie]

thanks
not got alot but goin back tommorrow but heres what i have.
cellar cooling evaportating at +5c onr407c
temp at bulb for tev 22c room temp 22c
evap coil only cooling at distributor,air on 22c air off 21c
unit runs for 5 min then cuts out on overload , compressor hot cant touch it
the compressor has just been changed and the customer informs me he has had at least 3 compressors in as many years

Suction pressure is to low for an air temp of 22C.
Pretty bad state of affair.
I bet the system is contaminated, wrong orifice or refrigerant charge, faulty TEV

[sean1]

i was thinking faulty tev/orifice , what would you expect suction pressure to be or how would you calculate it?

[mad fridgie]

i was thinking faulty tev/orifice , what would you expect suction pressure to be or how would you calculate it?

You need to think of this in a different way.
Get away from fixed figures.
If this is a beer cellar, then the system would have been designed to run at 10C (well it was 20 years ago when I lived in the Uk).
Your cellar is is at 22C (and is likely to have humidity), so this is under pull down load. So you would expect your suction pressure to be high, also a much higher head pressure (presume ambient is high, are you having a good summer) and a hottish liquid line.
You would also expect higher superheat (load is likely to be higher than system capability)
Electrical power draw will also be high (current)
Think of your system as circle, you change one part, then the the rest will change.
If you want to ckeck your superheat whilst the cellar is still hot, block of some of the air going through the evap. (I used to place beer cloths over the fan to restict flow) You should then see you SST and your SCT drop, then your valve will start to operate on the superheat.

[cool runings]

thanks
not got alot but goin back tommorrow but heres what i have.
cellar cooling evaportating at +5c onr407c
temp at bulb for tev 22c room temp 22c
evap coil only cooling at distributor,air on 22c air off 21c
unit runs for 5 min then cuts out on overload , compressor hot cant touch it
the compressor has just been changed and the customer informs me he has had at least 3 compressors in as many years
just want a few ideas when i go back

You need to fit gauges to both suction and discharge...

Is it condensing correctly??

all the best

coolrunnings

.

[NoNickName]

mad fridgie got it. In a commissioning phase, when the temperature on the secondary side are higher than expected, evaporating pressure AND superheating can be both high, or when evaporating pressure is ok (because of MOP TEV), superheating is excessively high.

[mikeref]

Only 1 degree c temp/diff across evaporator? Is the compressor semi or dome type and what is the discharge pressure and liquid temperature before compressor shutdown?