Lost!

[tman39]

Hello All,
My name is Tim I'm new here. I am currently a bit baffled. I was asked to build a small blast freezer with some old stuff from the bone yard. Maybe my calcs are a bit off or I was just hoping for more.
what I have is a stainless steel box 18"wx110"lx44"h.. have a Copeland discuss 3083-0750-tfct.

I have 2 evap coils, with 8x1/4 dist on both. coils sizes are 28"x25"x 10"thick.

sporlan valves sse 4-zp

refrigerant 404a

I am running a 170-175 head 25- 15psi suction with an 8 degree super heat.

I played with the superheat a degree or two up and down.--suction line sweating nicely

I was hoping to achieve -25 to -20.. i can run -12 to -15 all day...no issues. but i would like to get into the neg 25 degree range.

Im not sure if trying to push this 7.5hp cond. too far or i sized my valves wrong. this is my first build.. i don't want to call it a fail yet.

[Royal241]

I was looking up the model number on compressor, can't find. can you repost the model number? I'm willing to spend a few minutes...

[Gary]

What are the entering and leaving air temperatures for both coils?

[Done it all]

To get the temp lower you need to get the evaporating temp lower, if its all cobbled together maybe your evaps are oversized for the comp. A quick fix could be to lower the suction pressure, by adjusting the valve or going for a smaller orifice, (this will increase the superheat lots) but may have the desired effect. Plan B: remove one of the evap coils, although then your problem may go the other way, too low evaporating.

[Gary]

The best way to reduce the evap temp is to reduce the evap airflow.

[monkey spanners]

The air off temp will drop with the room temperature, if it reaches a plateau then thats as good as it will get unless something changes. In other words if you have a good temperature drop across the evaporator but the room doesn't get any colder the system is only keeping up with the heat load of the room and contents.

As your system is made of spare parts the stalling in temperature drop could be due to undersizing, missadjustment or selection or equipment working outside its design envelope.

Have you calculated the duty you need and compared it to what your compressor and evaps are rated for?