Broken fridge; need refrigeration engineer help for insurance and maintenance purposes. Many technical geeky issues involved. Long post follows:
My house came with an expensive Subzero 550 refrigerator/freezer.
During our recent Vermont floods, power was off for two days. The refrigeration compartment got to room temp (about 65F), with a medium payload. We were out of town during the outage.
The freezer compartment was set to –12F, and its contents stayed fairly frozen, if I use the ice tray as an indicator.
After the power returned, which was just before we did, the fridge failed to attain temperature, and when I measured it with an Omega HH303 thermometer, it showed about 60F. After a full night of operation, it was still in the high 40’s.
Calling a repairman, he blamed the problem on a clogged evaporator, which replacement I am currently awaiting. (BTW, Subzero/Wolff Company is providing this at no charge, out of warranty! Nice touch, folks. I am impressed!)
The tech showed me a pressure reading of negative 5 PSI where a positive 10 should have been visible. Not sure what the measure point is, but it’s where he connected his combo gauge. It uses R134A refrigerant.
I’ve been monitoring the empty unit for the last two days. A graph of the time/temp curve is here.
I warmed the interior to room temp the night before, and I’ve been running it since, with only two door openings, clearly visible in the graph. This is with the temp setting at 5 on a 1-10 scale (i.e., mid scale).
Here’s the question:
It appears to be regulating, but the hysteresis seems excessive, and its cooling rate is too low. Specs on the sealed system indicate 280 BTUs, which seems small if it means 280 BTUs/hr.
A long time ago, I wrote software for a cryo freezer (-190C!) using combo Freon/ammonia refrigerant and recall something called “de-logging”, which was a 10 minute break in compressor operation per 8 hours of constant operation during pull down. I am sure this Subzero doesn’t have a de-logging feature. It was to prevent compressor oil from gelling. The tech on my unit blamed oil as the culprit in the blocked evaporator.
I need to build the case that the unit is broken because it ran excessively without a delog feature, traceable to the power outage and resulting cool down demand. I also would love to know if there is any way to clear an oil clog in the evaporator without replacement. I have access to the entire evaporator surface (from the front), and the unit is obviously sufficiently charged.)
Any/all advice info greatly appreciated. I am an electrical engineer and know enough about refrigeration to get frostbite. Thanks in advance!
(Note: I posted this on a refrigeration engineering site, too)