r22 walk in box

Paul S_3

hey everyone....i really do not work on refrigeration....im doing a friend a favor who has a service contract with me for the hvac of the building....its a i guess med temp walk in box should maintain about 38-40 f.....the condensor on roof is r22....this is a temp controlled pump down system .....i guess thats what it looks like??today i walked into the walk in box and just the evap fans were running....it was about 55 f in the box....i went to the roof and found the low press control open....lpc is set for 30psi cut out and 75psi cut in...compressor rla is 4.8A rated for oper MAX  6.7A.....i just want to know if these pressures and temps are correct and if the LPC is set right.....another refrig tech who was working on the next store told me the LPC should be set at 10psi cut out and 30psi cut in....i really do not work on refrigeration and i know its R22 , i do not want to go by A/C measurements.....system has a txv, a solenoid at the evap....and its about 25 f outside.....thank you                           i will p[ost piuctures on next post

PAUL S 

Paul S_3

walk in box

Here sight glass...a little bubbly

Paul S_3

more

Lpc

Techman

AC vs REFRIGERATION

Sure thing you go by your AC mearurememts. Just slide up / down on the same P/T chart! At 32*box temp,( comp is off) the R22( evap coil) pressure on your gauge will read 58.7psig so at 75psig ,that cut-in will cut-in at 44-45*. One of the rules of AC is 32* is into the danger zone. When was the last time you had a running AC unit with lower than 60psig ? This is for residential AC.

Paul S_3

r22 walk in box

this is a walk in box....that im working on im asking as you can see on the gauges are these readings normal for refrigeration....the box is cooling now...i would assume readings would be different your passing MUCH cooler air through the evap

Techman

Not so fast.

You have the lp control set to maintain a 44* box .If you are looking for a  38* w-i. box the cutin would be set at 66psig = 38*f .Now you have a "pump down"set up which means two things .One is the thermostat is in control and two is you lower the lp control cutin away from the P/T point of 66psig . And what were you saying about the air temp? There is a TD just like AC , 75* return air w/ 55-60* supply or  38* return air temp means 18*supply air temp ,KindaSorta.

Paul S_3

r22

i was saying does the low pressure side psi look normal??.....the thermostat (closes on a temp rise) is wired to the solenoid valve....i thought the LPC just shuts down compressor during pumpdown.....on this application....so you are saying there are applications that are just controlled by pressure and you set the cut in to maintain walk in box temp???.....sorry do not work on refrigeration...alot....and the temp split with R22 should be btween 17-20 f.....but what about temp split with a r404 system that does the freezer next to it....would like some more knowledge with this....thank you tech

PAUL S

Techman

Temp Diff

On refrig/freezing/extra low freezer  the air temp TD is KindaSorta 10*-25* depending.The t'stat calls at 38* but the LP doesn't call until the box warms up to 44*=75psig ,so ,yes, that LP control is set wrong .And that MI/SG doesn't look kelly green or are my eyes off?

Paul S_3

thanks

thank you for all your help.....it is green the sight glass

Eugene_Silberstein

Pump Down vs. Pressure-Controlled System

You can use the low pressure control in two ways to control, either directly or indirectly, the temperature in a walk-in box.



By using the pressure control by itself, without a pump down, you set the control as follows:



Determine the desired temperature range in the box. In your case, you want the box to maintain a temperature between 38 and 40 degrees.



The cut-in setting on the pressure control will be set at the pressure that corresponds to the highest desired temperature in the box, namely 68 psig at 40 degrees. This is found on the P/T chart as the compressor is not operating and the evaporator coil will be at the same temperature as the air in the box.



The cut-out setting on the pressure control will be set at a pressure that corresponds to a temperature that is roughly 15 degrees cooler than the lowest desired box temperature. This is because the compressor is operating while the box is pulling down and the evaporator coil will be approximately 15 degrees cooler than the box temperature. In this case, this pressure (46 psig) will correspond to a temperature of 23 degrees, which is 15 degrees cooler than the lowest desired box temperature of 38 degrees. If the pressure control has a high event (cut-in) and a differential setting, the cut-in will be set at 68 psig and the differential will be set at 22 psig (68 psig - 46 psig).



Now, with an automatic pump down system, the rules change. The primary purpose of a pump down system is to remove all (or most) of the refrigerant from the evaporator before the compressor cycles off. This is intended to prevent liquid floodback to the compressor when the system goes back into refrigeration. In this case, the cut-out setting on the pressure control should be set at a pressure that is close to zero, but not low enough to pull the low side into a vacuum. This will prevent air from entering the system in the event of a low-side leak.



The cut in pressure setting is somewhat random, since the closing of the low pressure control is intended to energize the compressor once the liquid line solenoid has opened and refrigerant pressure has built up on the suction side of the compressor.



Your colleague's advice on a 10 psig cut-out and a 30 psig cut-in is fine, but personally, I would go with a cut-out closer to 5 psig as this will remove more refrigerant from the evaporator coil before cycling the compressor off.



Hope this helps

Paul S_3

thanks

Thank you guys...this helped me alot...much appreciated

Paul S

Techman

Paul S

Why is that R.H.cond fan motor not running? And are you sure that MI/SG is a nice deep green? There are many shades of green that the MI gets, but only one shade is proper.

Paul S_3

techman

Condenser fan not running because of a control it looks like a roll out switch...I guess its for if outdoor ambient temp gets to cold....it said 70f on the switch....and as far as the sight glass I will check tomorrow for that deep green....if its a different shade that well indicate moisture present in the system?

Paul S

Techman

Low ambient operation

requirers  somesort of minimum head pressure control and it looks like there is a "headmaster" device in the upper lefthand corner of the picture.I use a lot of the HH version of the C-163 filter/drier. The HH is for acid cleanup. Acid gets created from moisture, and moisture is anything less than a nice kelly green M/I.

Paul S_3

techman

The condensor fan is off by a small switch in the electrical compartment....and as for that valve in the picture what exactly does it do....its a three way valve and comes right out of the condenser coil right before that liquid reciever ?...or Is it a accumulator? And what is''HH'' your talking about

Techman

`Refrig

Is that a new compressor? If yes, what happened to the old comp?

Paul S_3

YES

yes it looks like a new compressor.....i asked the customer and he said that the last one just failed....doesnt tell us much...that 3 way valve in the top right of the pic ....what is that ???

PAUL S

Techman

Head pressure

.That device controls the head press in cool/cold weather operation. And ALL freezer comps need air impingment on the comp body so I would fire up that other cond fan motor.If not you will kill the comp.

Paul S_3

not freezer

its not a freezer its a refrigerator r22 walk in box....should i still fire up that other condensor fan motor.....even though there is a control in the unit that the manufacture put in there to control 2nd fan motor.....???

PAUL S

Techman

WI Ref

If the mfrg put in a fan cycling control then so be it. What brand and mn# is the cond unit? It doesn't make sense the mfg put in a "head master " and a fan control.