Icing Up

[walden]

Can an electrician ask a stupid question?

Just been to a small ice cream store with a single evaporator with electric defrost heaters.

The coil keeps becoming iced-up. Ice is bulging out of the back of the coil. I have checked the settings of the Eliwell ID974 controller: the defrost heaters are all connected and each leg of the heaters has been checked with a clamp ammeter and all are carrying the correct current and all within a few percent of each other. I can find nothing electrically wrong.

Here’s the question: what, on the mechanical side could be the problem?

I ask so that I can understand more about the dark side of refrigeration!

[paul_h]

Here’s the question: what, on the mechanical side could be the problem?everything or anything!
Not enough refrigerant, fault in control of refrigerant, not enough work for the refrigerant to do.
You need the tools we have in our trade (gauges and thermometers) to find out which.
First of all more information is needed on the system. Capillary or TXV flow control?
Fan forced or static coil?
Cabinet or room?
Defrost teminated by temperature or time (or whichever comes first)? Y

ou've tested the heaters, but what about the controller/timeclock etc, does it actually turn them on? I know nothing about the eliwell, I'm only familar with mechanical clocks or carel, dixell and lae electronic controllers. But controllers are often temperature sensitive. If a sensor is bung and says it's not cold enough to defrost, it won't even attempt one, regardless of with the timer/controller wants to do.

[dkemper]

First, how long (and often) do the defrost heaters run for and are the compressor and evap fan(s) shutting down during the defrost?

On the defrost side, it's possible the defrost is not running long enough, not often enough, or the compressor is still running refrigerant through the evap while defrosting.

On the refrigeration side, it's possible the system is low on refrigerant, has a problem with it's expansion device or at worst, is built of mis-matched components.

Purely mechanical, does the evap fan(s) run at it's rated RPM? Inadequate air flow across the coils will cause icing issues as well.

Has the system ever ran and defrosted correctly? If so, any ideas what has changed since then?

[acb]

Hi Walden,

I know this controller very well, what are the defrost setting on this, and if youre not all that sure about refrigeration how do know if the controller is set up properly? If you can provide information on this and anything from the other posts, I might be able to help you.

Regards

Alex

[Electrocoolman]

Walden,
Start with the basics first (as mentioned by my colleagues above) unless you know controller has been 'got at'!
Does evap fan run normally? ie door switch interlock OK? Fan motor OK?
Is evaporater blocked with dirt such that airflow is restricted?
Is drain pan draining correctly or full of ice?
Is system LP switch u/s. Does compressor stop during defrost?

There is no substiute for experience - approach it logically.

[mambro_01]

hello Walden,

of course you shoul refer to the OEm in order to get the correct settings for ID controller.
Maybe DST or DET are set too low, so it's enough to increase them

regards