We received a call to one of my supermarkets, a fairly generic “Host Comm Error,” meaning something was wrong with the Danfoss rack controller. No big deal, right?
Not so. I walk up to a dead silent rack house, the stuff of my nightmares. Rack A, low temp, and Rack B, medium temp, stone cold dead. The Danfoss controller is dead. I assumed that a fuse was blown, breaker tripped, killed the controller, turned the racks off? No big deal, right?
Not so. I trace the wires out and behold, it’s drawn from Rack B power, not an independent circuit (as it should be). I check the 200 amp breakers for the racks. Rack A, tripped. Strange, since it’s not the one that powers the controller. I reset it. Check the voltage, 480 volts across all legs. Fantastic. I check Rack B. I hear sizzling. I stand back, alarmed, but check voltage. 480 from leg 2 to leg 3, 480 from leg 1 to leg 2, 50 volts from leg 1 to leg 3.
Shit. Ended up cutting up an extension cord to plug the controller in, get Rack A running. Call the electricians, pull the panel apart, one leg of the Rack B breaker is burnt and melted. The boss shows up, and it’s not looking good for that new breaker. We order a generator to run the rack, as a precaution. Two refrigeration mechanics manually running the racks, two electricians trying to find a 200 amp breaker, a generator mechanic, a separate electrician to wire in the generator, managers in and out constantly, reefers rolling in.
Finally found a 150 amp breaker that would serve temporarily. Get the racks back up and running. 8 hours later.
To add insult to injury, this same store had another catastrophic failure just a week ago. Rack B discharge transducer failed, read 0psi. The condenser shut off entirely, and the controller ran the compressors flat out. The old rack, which has been through several contractors, had all of high pressure controls fail, and so the compressors ran and ran and ran. One transducer, and 700 pounds of gas later, that day was done.
So, on call mechanics, how was your weekend?
Julie Mendez's Blog 
![[link]](https://i.redd.it/nmxh59l4a9271.jpg){kind=link}