High Capacity problem

[scorpx]

Hi all
I have a little problem about 20hp 404A compressor

There is a different 0C room connected to 1 x 20hp compressor.

Compressor have 2 step

There is no problem when compressor working with full capacity for 4-3-2 room

but when only one room working. Suction is getting low and compressor stops.
(only one step working)

How can I solve this problem. is there any idea

[texas64]

Is there an low pressure adjustment on a low pressure mechanical control or if there is electronic controls to make an adjustment lower. First, the refrigerant charge must be correct before you make adjustments.

[scorpx]

there is a dixel xc650c capacity control digital.
I adjust it. but when 1 room left. suction is getting low and capacity controler stops it. actually suction must be 3.3bar but i adjust it 2.5 bar. but suction is getting 2.0 and capacity control stops the compressor.

[texas64]

Is it only the same room that gives this problem or is this low pressure problem with any "one" room? Does each room have an "EPR"(evaporator pressure regulator)? How is the discharge pressure doing? Is it changing also whenever the problem happens?

[texas64]

Are you sure that the unloader(step) is actually working? Your compressor could be operating on full capacity even with one room, hence the low pressure.

[scorpx]

-don't have pressure regulator.
-I am sure the unloader(step) is working
-it in not the same room that gives this problem when one room left.

if I use 1 Danfoss KP1 and 1 selenoid valve between suction and discharge, when the suction preessure getting down selenoid opens for by pass ? can it solve my problem ?

[RANGER1]

-don't have pressure regulator.
-I am sure the unloader(step) is working
-it in not the same room that gives this problem when one room left.

if I use 1 Danfoss KP1 and 1 selenoid valve between suction and discharge, when the suction preessure getting down selenoid opens for by pass ? can it solve my problem ?



Scorpx,
If you do this you will overheat compressor & cause damage.

What type of compressor is it, how many cylinders?
Can you instal another unloader?
Is it a semi hermetic or open drive?
Is it a cool weather problem?

[scorpx]

Compressor is Refcomp Sp4L200E 20Hp semi-hermetic 4 cylders.

thanks RANGER1

if i use pressure regulate valve instead of selenoid valve. Same overhead problem appears ?

you said "Can you instal another unloader?" for what ? i don't understand the why you write it.

[savoc]

may be check your unloader solenoid to see if the capacity control is working, can you fit and extra unloader to compressor? some compressor have this option might need a new head cover plate. when fully unloaded be care that they comp dose not over heat. An other option is to fit a vsd with a electronic pressure tranducer on the suction line. I have see many plants running vsd these days. from ammonia screws to freeron recip comps. set up correctly they run sweet.

[mad fridgie]

Without knowing all the plant details and controls some simple ideas
VSD (expensive)
Lifting discharge pressure at lower load (reducing net refrigeration effect) need to be careful that the comp remains within the unloaded envelope.
Hot gas by-pass on each room (lots of hassle)
Common hot gas by-pass and TEV to de-superheat. ( hot gas injected into main suction, then liquid injected after to reduce superheat) not a bad option

[texas64]

Have you lowered the capacity control as low as it can be set to see at what point the compressor will remain operating? As long as it is operating, it would be able to pull down the temperature of the "one" room.

[simon@parker]

was the system designed to run with just one room on it ? or is it supposed to run all the rooms ? could be that all rooms need to run or you are going to have to fit modifications :)