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I've seen cases not icing at 60%. Ususally they will though.

MOst cases I am familiar with work into the 50-55% range at store temps not exceeding 75 degrees. Remember Relative Humidity is just that....Relative. At a higher temperature the same RH actually means a higher moisture content in the air.

If the open freezers you are talking about are multi-deck freezers and you are having trouble with excessive frost build-up, try looking at the ambient and secondary air bands. Make sure they are in good working condition. This is how the store air is kept out of the freezers in the first place. If these are not working because of fan motors out or dirty honeycomb grills, this could be your problem.

If the open freezers you are talking about are coffin cases, look for air infiltration from sources like supply registers from the a/c system.

kysor-warren rates most of there cases for 75 deg. F 55% relative humidity

55%. But higher than normal temps around open MD frozen case or SD cases will suck in the warmer moister air and there you go.

On glass doors we have an anti sweat control panel that pulses them. Older stores use humidistats.

I'm having trouble with case coils icing up and wondered if too much humidity would do it. I measured 40 0dd % today.

You talkin' bout frosting door glass? Or you speakin' bout abnormal ice on the coils?

Or...you mean that type of excessive humidity where the cases are sweating so bad the store director claims there are drains overflowing?


If the A/C isnt up to snuff, you will have all of the above.
I never measured it, but I imagine around 50%.

Next week I'll buy me a humidity meter and start taking measurements in the stores.

above what % of relative humidity will open low temp cases start to be affected by icing etc?