Low suction pressure

[samjohn]

Hello! Can anyone tell me why I'm getting a good discharge pressure (185) but the suction pressure pulls down lower and lower as I get my water down to target temp 31 degrees F)? It's an RSW system using 507. Sight glass on liquid line shows full liquid. Pretty sure I have superheat set right (approx. 10 degrees).

[NH3LVR]

Because the load is dropping off as the water cools.
Unless you have unloaders or hot gas bypass.

[RANGER1]

31 deg F water, what type of evaporator do you have?

[samjohn]

Nh3lvr, sorry about taking so long to get back to you. At sea now and satellite connection is spotty. It makes perfect sense now that you said it.
Grizzly, the evaporator is a shell and tube design. Stainless shell with titanium tubes. Refrigerant in the tubes. Not sure of the make or size. Designed to chill salt water in fish holds. Submerged in hold

[RANGER1]

Nh3lvr, sorry about taking so long to get back to you. At sea now and satellite connection is spotty. It makes perfect sense now that you said it.
Grizzly, the evaporator is a shell and tube design. Stainless shell with titanium tubes. Refrigerant in the tubes. Not sure of the make or size. Designed to chill salt water in fish holds. Submerged in hold

Depending on salt concentration in area you are in it could. E freezing water in heat exchanger as well
Refrigerant pressure in evaporators will dive once freezing occurs, have to. E careful not to damage equipment

[Grizzly]

Nh3lvr, sorry about taking so long to get back to you. At sea now and satellite connection is spotty. It makes perfect sense now that you said it.
Grizzly, the evaporator is a shell and tube design. Stainless shell with titanium tubes. Refrigerant in the tubes. Not sure of the make or size. Designed to chill salt water in fish holds. Submerged in hold

ERR! you mean Ranger1.
Grizzly

[Grizzly]

Just a thought Samjohn.
Have you considered partially blocked evaporators.
Unless you have a very efficient filtration system. Your sea water circuit will clog up over time.
Reduced water flow through the evap will result in LP overshoot.
Lower suction pressure with the above fault is quite common.
Check your pump circuit strainers also!
Grizzly

[Grizzly]

This might happen due to the fact that the load is dropped off as the water cools. It works fine unless the unloaders or the hot gas pressure bypass through the low suction pressure to let it work well again.

Why are you posting so much with biennial answers or copies of what has already been said!
Maybe you would like to give us all some history of your experience.
Because at the moment I and others are concerned about the trend and content of your posts.

In fact if the quality stays as poor as it is I will have to consider deleting your posts.

Grizzly