Capacity Control Pressure Settings

Hi Guys!

I am looking for some advice on how pressure switches should be set. I am working on a system with a freezer room and cold room. Freezer set point -20 and cold room set 4 degrees. The compressor has capacity control (50/100%). The gas is R404a (30kg).

The suction pressure is always around 1 Bar until it reaches temperature and pumps down.

LP switch is set for 1 bar with a differential of 1.
The capacity control switch is set for 2.5 bar with a differential of 0.5.

Can anyone tell me if these are the correct settings? I am relatively new to the trade. My understanding was that if its running around 1 bar it should be on @ 50%. Then if the suction pressure was to rise (for example) to 3 bar it would kick in to 100% capacity again to bring it back down to 1 bar?

The system always runs at 100% capacity no matter what, i don't think this is right?

Any information appreciated, Thank you.

KegSalad,
If you have app for pressure temperature or chart, convert pressures to saturated temperature for that refrigerant.
The pressure/temperature should be 5-10 deg C lower than your room temperature.
Mid any lower then is to cold & probably unload compressor.
Prove that unloaded actually works & behaves by unloading when pressure lowers & loads when pressure increases.
Try all that & see what you come up with.

.

The issue you have is the 2 temps in the 2 cold rooms.

The freezer will need an evaporation pressure of 1 - 1.5 barg and the fridge should be at 3 - 4 barg. Do you have evaporator pressure regulation fitted to the fridge side of system?

It's not good for the fridge to run with the same pressure as the freezer. Then because you have 50% - 100% capacity control you basically have all or nothing. If it is running continually it is because the load is there and the demand is there.

Does it have evaporator pressure contol?

Rob
.

Hi there,

Thanks for the replies.

Yeah there is an EPR valve fitted to the cold room and this is set to 2 bar?

I just thought when running at 1 bar suction the compressor should only be running @ 50% load.
Then when the suction pressure rises to 2.5 bar it will cut in @ 100% load to bring it back down.

Is what i'm thinking right? Or am i on the wrong track here?

Thanks in advance for any info.

Kegsalad,
Check my earlier post & see what you make of it.