I got a call from a meat market customer Thursday at 5:30 AM shortly after the deli kitchen crew came in. They said the store had a burning smokey odor and the 3-door reach-in freezer was making loud popping sounds and flashes of light.
Fortunately, they managed to find the breaker for that case and shut it down. I arrived a while later to find this:
Note the melted temperature control knob:
Lot's of smoke staining too. (Yes, that's one of my TEV conversions):
The product on the lower four shelves was still hard frozen. The stuff on the top shelf was not only thawed, but actually cooked.
Can't figure out what the heck this fuzzy crap is on the doors:
Got the coil plenum down to see what was going on up there. Note the insulation dripping from that brown wire:
Then I found the source of the terribly acrid smoke. The melted wiring had shorted to the evap coil blowing several pounds of R404A and a bunch of POE oil into a glowing maze of defrost heater elements. It's hard to see, but there's a hole in the top front return bend.:
Of course all this fried wiring goes up into the box insulation in the top and ends up down at the right front bottom of the box. No repairing that.
How did this happen? This case had no defrost limit thermostat. I'm still not sure how it all started, but it certainly wouldn't have gotten this far if the case were designed to have a safety limiter for the heaters. (It has one for the door frame heaters but not the defrost heaters....go figure)
One of those wires short out on the u-bend?
I’ll bet the solenoid coil on the clock is swelled!
Yes, a wire shorted to the return bend. You can see it best in the next to the last pic...that spot on the copper is melted insulation, the burn hole is at the top of that.
Originally Posted by pecmsg
The solenoid coil looked OK but even if the termination failed the failsafe was set at 30 minutes should have de-energized the defrost heaters.
The contacts on the timer were pretty well pitted and burnt. I'm theorizing that the #3 contacts were welded together but broke apart after things cooled down.
In any event, I'm adding a defrost limit thermostat so this won't happen again.
I wonder how this design ever passed UL?
That just completely blows my mind... I can't wait to start posting my pictures on here...
"The truth only hurts when it should"
There should have been a delay and a limit in that case, I confirmed it with Ron T yesterday.
He did mention that two models of the newer GDM and T series do not have the delay.
Do you have a model and serial of the case?
Coldcube, Here you go...
Here's a pic of the wiring schematic. No limit for the defrost heaters, just the door heaters:
I can't agree more about the limiting thermostat,I have been adding them whenever I come accross a freezer that doesn't have them.I also never ever cancel DTTs.Learned it the hard and scary way a couple of years ago at a BP gas station store.
Hopefully it can be noticed that there is a defrost termination problem when there is a limiting thermostat though..Before it fails in the CLOSED position.
Well at least they didn't use a Hydrocarbon refrigerant or it could have been much worse.
Would the last person to leave NJ please put out the lights
I followed up with Ron T today.
The case is from 1996. At that time a termination/delay was all that was required for "safe operation". Just on a side note, any changes to the case, including the addition of an expansion valve and receiver will void warranties and the UL stamp.
Before I get barbequed, I personally understand the benefit of the expansion valve.
“If You Can Dodge A Wrench You Can Dodge A Ball”
Must have been a real chinese firedrill in that kitchen when that was goin on! best to replace box? i would!! good luck stan
Keep it simple to keep it cool!