r404a small water-cooled marine freezer

[keithholstead]

Dear Forum:
I just built and installed a small refrigeration (freezing) system for my boat. It is my first system. The evaporator is of holding plate type with 3.6 gals of eutectic glycol solution (30% Gly/H2O). I didn't have a charging scale so I went ahead and followd standard procedures and got the unit running at 184-185 PsiG Hi side pressure and average 40 PsiG low side with unit running. After the unit has been off for several hours and begins to come back on, it short cycles several time (two or three) and then smooths out and does fine. My water in to my condensor is 72 deg F and water out of it is 76 deg F. My TXV is set for 9 deg F. My box is well insulated but never seems to go below 30 degrees.

My questions are this:

What should my hi and lo side pressures be for ideal operation?

Do you think I need more refriogerant based on the short-cycling?

What would be a good differential on cut-in/cut-out pressures on the low pressure control?

Any help will be greatly appreciated.

[keithholstead]

Okay, I admit I've surmised that the water cooled condensor is 76dF (water out) and 72dF (water in) so adding 15 dF to 20 dF for water cooled I should wind up with a head pressure of 205 to 230 PsiG. The problem is that this an old "heat pump" coil with subcooling on suction vapor. The compressor is aan AE -94422Zxa comprssor rated for 20 dF duty (med. commercial). Should I give it the extra gas to bring it up to normal head pressures or leave it at 195 PsiG. Or should I add a receiver that this system does not have?

[taz24]

Should I give it the extra gas to bring it up to normal head pressures or leave it at 195 PsiG. Or should I add a receiver that this system does not have?

How are you controling the discharge pressure?
Do you have a regulator valve regulating the flow of water through the cond?
If you do not regulate the flow of water the discharge pressure will be low.

I would fit a sight glass to the liquid line and a condenser water flow control valve to the system.
Then you will be able to see the correct charge and also control the head pressure.

taz.

[The Viking]

There are a lot of variables there....

As you state that it's your first system, installed on your boat from second hand bits, I sort of assume that you not are a fridge engineer.

To set this system up you will need experience, it's nothing I would expect any of my apprentices to be able to do during their first years...

Maybe you should find a friendly fridge guy and ask him (or her, let's not be sexist here) to have a look at your system and advice you on what to do.