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AzRob
17-09-2007, 05:03 PM
46 foot freezer trailer modified to be stationary with condensing unit on the ground under the trailer. System has two evaps, one 4 fan and one 3 fan unit. I noticed box temps dont get below 25f degrees in the heat of the day (runs 24-29) and early morning hours has box temp of 20f degrees.
System was designed by a local Refrigeration outfit here in Arizona, has been frzing product to -5 in the past, apparently designed for that box temp.

Quick look at the system, I observed the following:

1. 408a - suction of 25 psi, discharge of 225. Ambient 100 degrees, box temp 27
2. One evap with no evidence of draining except early morning hours and not much at that. (puddle on the ground minor and only evident in early morn hrs, other evap..plenty of water during defrost) Good air flow through both evaps, one not draining not frozen up.
3. Seems to be one LLS supplying both evaps, noticed no other special controls persay.
4. Bubbles in sight glass.
5. Door (roll up) seal at top shows light all the way across.
6. 5HP compressor
7. Defrost 4x per day, dont know duration.
8. suction line slight sweating at condensing unit, liquid line warm @ condensing unit.
9. Unit runs constantly except at defrost. Stat set to -5.

Im wondering a few things:
1. How does dual evaps play on the gauge readings? If one evap is having problems, do the gauges show an "average" between the two?

2. What evap temps would be expected for a box that sits in the hot sun all day? How to determine apprx gauge readings for this system.
Im leaning toward evap prob...the one thats not condensating. Think Im headed in right direction? Tad different system than 4-5 ton residential A/C's with fixed orfice!

Dr._Fleck
18-09-2007, 05:53 PM
Sounds like one evap is starved of refrigerant, but i'm puzzled about the high head pressure. Is the condenser clean? Is the condenser unit the correct size for the two evaps?
Also because it is a short pipe run i would have thought the suction would be icing under normal conditions... Another indicator of low refrigerant.

Make sure the condenser is clean to try and get the head pressure down before putting any more refrigerant in.

John Hunter
18-09-2007, 10:52 PM
Hi I am new to this forum , but find it of great interest. I am involved in Industrial Refrigeration.
In a DX system with a low level condenser it is important to ensure the system is balanced . For example if the liquid supply pipe is a bare pipe open to ambient conditions , it s possible for the pressure at high point to be greater than at the condenser liquid outlet. This condition will cause liquid flow problems and a liquid lock up condition in the condenser leading to very high compressor discharge pressures.
The sweating on the condenser to some degree indicates excessive sub cooling due to the retention of the liquid being a problem.
To over come these problems sometimes the location of the condenser has to be looked at or at least ensuring that a balance line is installed .
I may have this all wrong but from the basic info it appears this could be a problem

AzRob
19-09-2007, 03:18 PM
Oops, typo, discharge pressure is 225, not 325! Its about a 102 degree equiv.

I dont think system has design problem as it has worked in the past. (worked being maintaining a -5 box temp in the hot sun..full load)

Suction line does ice up, but at the condensing unit its condensating only. Havent been back out there in several days now.

dkemper
20-10-2007, 01:29 PM
Check the superheat on both evaporators, I agree with Dr Fleck, the one evaporator appears to be starved of refrigerant.

Possibly a duff power head is keeping the expansion valve from opening properly.

Bones74
02-11-2007, 02:59 AM
I agree with the superheat. But don't adjust a TXV when the system is a leaker. it will only give you a false sense of the pressures and charge. And did it run fine in the winter? or is there a specific time?:cool: