Walk in ac freezing over

[Tnordmann]

Hello all!!

So I built a well insulated walk in cooler and I am cooling it with a window air conditioner unit controlled by a STC-1000.

My Problem: The ac unit freezes over and fails to cool the room.

What I’ve tried: I’ve tried having a fan blow over the coils to evaporate moisture. I’ve tried installing a dehumidifier. I’ve tried taping a 100 watt hot lightbulb close to the coils and having a fan blow the air to melt ice. All have failed to fix problem.

New Solution: (and this is the part I would like input on) I’ve re wired the AC unit so the fan in the AC unit is always running even when the compressor is off. My theory being that continually drawing in air will keep the coils from icing over. I won’t know if this will work untill I show up to my work shop tomorrow morning. In the mean time I was wondering what everyone thinks about my “fix”.

 

[pillswoj]

Is it an old unit? Coils freezing are often a symptom of low freon level (or whatever the coolant it now a days)

 

[Tnordmann]

Is it an old unit? Coils freezing are often a symptom of low freon level (or whatever the coolant it now a days)

Thank you for taking the time to chime in. Yes, I’ve read that low freeon levels can and will cause freeze overs. This unit 4 years old but only used for 8 months.

 

[meadmaker1]

Low charge, low air flow, and low temperature will cause iceing coils.
Continuous fan will help. Be sure the coils and filters are clean.
Try 5 degrees warmer. Shorter run times will help
Run it where it has a warmer return(incoming air) temp, if its low on charge it should still freeze.
The trick to using this type of cooler for this purpose is to over size it. By over sizing the unit has short run times. At 55 to 60 degrees the unit has time to thaw before running again. If the fan runs continuously the coil stays dry and moisture stays in the air keeping humidity up.
The light bulb is a heat source that your ac will have to over come.
Units built for this purpose has very high air flow compared to home heating and cooling units.

 

[Tnordmann]

Low charge, low air flow, and low temperature will cause iceing coils.
Continuous fan will help. Be sure the coils and filters are clean.
Try 5 degrees warmer. Shorter run times will help
Run it where it has a warmer return(incoming air) temp, if its low on charge it should still freeze.
The trick to using this type of cooler for this purpose is to over size it. By over sizing the unit has short run times. At 55 to 60 degrees the unit has time to thaw before running again. If the fan runs continuously the coil stays dry and moisture stays in the air keeping humidity up.
The light bulb is a heat source that your ac will have to over come.
Units built for this purpose has very high air flow compared to home heating and cooling units.

Thanks for the helpful info!

 

[jburtner]

This is the controller I have seen referenced for diy window unit cooler rooms -

https://www.storeitcold.com/product/coolbot-walk-in-cooler-controller/

Cheers!
-jb

 

[Tnordmann]

Hi all. Ok. I’m calling it a fix. The problem with most thermostat override system is that they turn the whole unit off and in to control temperature, and this means there is no way to have the internal fan running even if the unit itself is capable of doing so. So I did rewire this unit so the fan wiloukd run continuously and the compressor would turn on and off with the thermostat control.

Before making my decision I monitored the temperature of the fins while the unit was in operation. The fins would be at their warmest when the air was being sucked into the unit and then the temperature would quickly plummet when the air circulating through the unit stopped. This in my view is when frost and ice had the chance to form. However with the fan always sucking in air it would continuously keep the fins and coils out of the “danger zone.”

Hope this is helpful to someone in the future.

 

[Winwil22]

A typical ac unit operates at 50 to 55 discharge temp or a 20 degree temp difference from entering to leaving temp that will require a 35 to 40 degree refrigerant temp. The longer a unit has to run to cool a space the more likely it will freeze up. So if using an ac unit. The bigger the better.