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View Full Version : walk in cooler evaperator keeps freezing up





ewart
16-07-2007, 10:02 PM
Hello all,
I am having this problem of ice build up for some times now, I have changed the thermostat, check the refrigerant charge and they seem ok ( low side 50 psi, high side 200 psi and no bubles in sight glass. Low side pressure will go down sometimes to 30. What could possibly be the problem????:

acb
16-07-2007, 10:27 PM
Hi There,
You have to provide more information, persistant evap ice build up can be caused by a number of things. What refrigerant are you using? Is it a chiller or freezer? Does the whole evap ise up or just a section of it? What kind of defrost does it have, hot gas, electric, fans only? If you can answer these I might be able able to tell you a few more things to try. If you are going to post, looking for help try and give as much information you can, Im sure people will try and help.

Regards

Alex

ewart
17-07-2007, 12:45 AM
First it is a walk in chiller using R22, when it ice up it starts from the bottom until it cover the entire coil and the unit is a chiller it does not carry a defrost cycle. one other thing i notice, the low side pressure would go down to 25psi at times when the room temp. is at 39 degree F

Electrocoolman
17-07-2007, 12:57 AM
Hi Ewart,
Does the door get left open or ajar per chance?
Do the evap fan(s) run OK or is there a problem with the door switch?
The other possibility is that the low pressure switch is wrongly set or is faulty (sticking).

Few ideas to start with.

ewart
17-07-2007, 01:21 AM
The fans are perfect i even change the pressure switch. The last thing i did 45 minutes ago is change the cut out point to 5 and the cut in point to 35

taz24
17-07-2007, 01:47 AM
First it is a walk in chiller using R22, when it ice up it starts from the bottom until it cover the entire coil and the unit is a chiller it does not carry a defrost cycle. one other thing i notice, the low side pressure would go down to 25psi at times when the room temp. is at 39 degree F


If it ices from the bottom up check the drains.
If the drains are blocked or restricted it could cause the problem.

Cheers taz.

paul_h
17-07-2007, 10:29 AM
As above.
Is there a lot of condensation or ice forming on the underneath of the drain tray?

old gas bottle
17-07-2007, 04:46 PM
should have a defrost system of some sort to be right,all you need is a time clock to switch the compressor unit off 4 times a day for about 20mins leaving the evap fans going,hot climate like yours i would say its a big yes?unlike us lot swaping our vans for boats !

Dan
18-07-2007, 01:56 AM
I am having this problem of ice build up for some times now, I have changed the thermostat, check the refrigerant charge and they seem ok ( low side 50 psi, high side 200 psi and no bubles in Sight Glass. Low side pressure will go down sometimes to 30. What could possibly be the problem????:


when it ice up it starts from the bottom until it cover the entire coil and the unit is a Chiller it does not carry a Defrost cycle

If this is a top fed evaporator, then an ice build up from the bottom is indicative of insufficient off-cycle time to defrost the coil. If you are not satisfying the thermostat with a 7 deg F coil, you have too small a coil for the duty you require.


The Fans are perfect i even change the pressure switch. The last thing i did 45 minutes ago is change the cut out point to 5 and the cut in point to 35

I cannot see any reason to have such a low cut-in pressure. If you do not have a defrost timer, your cut in should be 65 psig or higher. If the thermostat calls for refrigeration when your suction pressure is below 32 deg F, you will not get any effective defrosting of the coil.

You may have an oversized unit as well as undersized coils from the data you provide.

Regardless, you absolutely need a defrost timer with this application.

Samarjit Sen
18-07-2007, 12:35 PM
Hi ewart, Could you please intimate what is the Room Temperature you are maintaining and what is the fin spacing of your Evaporator Coil.

Andy W
18-07-2007, 06:19 PM
Are you controlling the temperature via a thermostat or pressure switch, is the evaporator perfectly clear ie good air flow.

Samarjit Sen
19-07-2007, 02:58 AM
In the event you are maintaining an Evaporative Temperature below 0oC, then there is going to be frosting on the Coil and the fin spacing should not be more than 6 per inch. If the Te is much lower, say about -25oC then the fin spacing should be 4 fpi.

I presume that you have a defrost system for the coil block as well as for the drain pan and drain line.

ewart
20-07-2007, 05:09 AM
I know that a defrost timer will make a difference but i have 11 other chiller without defrost timer and they are working perfect, I like the idea of changing the cut in setting to 65 psi. i think i will try it and let you know the out come.
If the expansion valve is flooding the evap. could it cause it to ice up???

Gary
20-07-2007, 03:09 PM
First it is a walk in chiller using R22, when it ice up it starts from the bottom until it cover the entire coil and the unit is a chiller it does not carry a defrost cycle. one other thing i notice, the low side pressure would go down to 25psi at times when the room temp. is at 39 degree F

A chiller is a machine which cools water. This is a walk-in cooler, not a chiller.

Why is the low side pressure dropping? Are the evaporator fans stopping? Is the liquid flow restricting? Is the system undercharged? Does the thermostat control a liquid line solenoid valve? Is that valve installed backwards?

The low side pressure should not drop. You need to find out why it is doing so.

Andy W
20-07-2007, 06:00 PM
A chiller is a machine which cools water. This is a walk-in cooler, not a chiller.In the UK we use the term chiller differently, open fronted dairy cabinet, chiller cold room etc, a machine which cools water to us is a water chiller.

ewart
20-07-2007, 11:39 PM
Hi ewart, Could you please intimate what is the Room Temperature you are maintaining and what is the fin spacing of your Evaporator Coil.

Ok i'm trying to maintain between 33-39 degree F and the fin size is 7fpi

ewart
20-07-2007, 11:52 PM
A chiller is a machine which cools water. This is a walk-in cooler, not a chiller.

Why is the low side pressure dropping? Are the evaporator fans stopping? Is the liquid flow restricting? Is the system undercharged? Does the thermostat control a liquid line solenoid valve? Is that valve installed backwards?

The low side pressure should not drop. You need to find out why it is doing so.

Yes the Tstat control a liquid line solenoid valve, The fans run non stop, The system have 50psi low side 200 high and no bubles in sigh glass (R22) Could the TXV BE THE PROBLEM????

Gary
21-07-2007, 01:52 AM
Yes the Tstat control a liquid line solenoid valve, The fans run non stop, The system have 50psi low side 200 high and no bubles in sigh glass (R22) Could the TXV BE THE PROBLEM????

A TXV problem is possible, but seems unlikely at this point.

When the thermostat reaches setpoint, the solenoid should close and the system should pump down and shut off. Does this happen or does the system keep running?

ewart
28-07-2007, 09:21 PM
Guys the last two things i did is relocate the sensor for the thermostat and adjust the superheat and it is perfect.

sylvester
29-07-2007, 04:48 PM
suction pressure will varies to the ambient temperature ie. day time -night time try to increase the suction pressure high enough so that you will not reach 30 deg suction press. with R22 @ 40 will start frosting
50 at day time may swing to a lower value during night time.

sylvester
29-07-2007, 04:59 PM
suction pressure will varies to the ambient temperature ie. day time -night time try to increase the suction pressure high enough so that you will not reach 30 deg suction press. with R22 @ 40 will strat frosting
50 at day time may swing to a lower value during night time.

acb
30-07-2007, 09:30 PM
Hi ewart,

Before the evap ices up and assuming the room used to work and its not new, does the room actually reach set point and unit switch off? if it does, sounds like a defrost problem. if the room reaches setpoint and unit doesnt stop, check solenoid valve or l.p switch.