Dr-Fix-It! Notebook Archive:
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| Basic Troubleshooting . . . My mentor in this business was Jerry. In one capacity or another, I worked with or around Jerry for about eight years. In a crisis situation, Jerry never got excited. When "stuff hit the fan", Jerry would just smile and take care of it. The only times I saw Jerry get nervous was when everything was working properly. "I like to see the enemy", he would say. Jerry's motto for basic troubleshooting was to check the basics first. It must be human nature to assume the worst. Troubleshooters frequently start with the worst case scenario and work their way back to the simplest solution. Jerry always said to eliminate the easy stuff before assuming serious, backbreaking, budget-busting repairs are necessary. For instance: Mel, one of our technicians recently ran into in the shop and breathlessly announced that a critical compressor running one of the main kitchen walk-in freezers had just hatched. His diagnosis was that the compressor needed to be changed out - immediately. I was suddenly looking at spending $3000 . But Jerry taught me that a good maintenance manager should always try to approach problems with a cool head and ask a few basic questions. Jerry always said it is moments like this when a good maintenance manager can be a real cost benefit to the company. Priority one: Stabilize the situation. Buy some time. Get some breathing room. Time, after all, really is money. Oh,I can probably find a compressor for this freezer today but I might have to pay special handling charges or drive my truck halfway across the state to get it. Maybe, I could have it air-freighted in. That would cost a bundle, huh? Then, we get to perform the repairs with overtime labor. But if I had the TIME, I could shop the price and delivery options and schedule the repairs during normal work hours. I told Mel, "Meet me over at the freezer. It will take me ten minutes to find a secure padlock and walk to the kitchen. In the meantime, inform the Chef that any frozen food he will need for the rest of the day will be pulled from the walk-in freezer immediately because when I arrive, I will be locking the freezer door. With the freezer door locked shut, the food will remain frozen for quite a while. That will buy us at least 12 hours- maybe as much as 24 hours." Priority two: Make sure to understand the problem. Start at the beginning and work to define the problem. Don't jump to conclusions. Don't assume the worst until you absolutely have to. After I locked the freezer and received my ration of grief from an angry Chef, I turned to Mel, "OK Mel, What is the problem?" "The compressor hatched." "Not so fast, Mel. Humor me. One step at a time. OK?" "Yes, Sir. . ." I summarized the situation, "The problem is that the compressor is not coming on when we think it should. Do we know that the freezer is calling for cooling?" "Yes", Mel nodded, "The contractor for the compressor is pulled in." "Is there power where we need it?" "Yes, All hot legs on the compressor contractor are energized. Both sides: line and load." "If the freezer is calling for cooling, the condenser fans should be running. Are they?" "No", Mel answered, "But they are on a capacity circuit. They operate according to discharge pressure so they wouldn't be on just yet." "Hmmm. Did you confirm the fans operate?' "No", Mel was starting to steam, "I didn't because the problem is with the COMPRESSOR, not the fans!" "Mel, How do you know the compressor is out?" "I powered down and checked continuity across all three terminals as well as to ground. There was no continuity to ground anywhere." "Good." ". . .But, one of the windings showed open." "You still have good power so no fuses blew. So, there probably wasn't any cross-winding short. But, an open between two compressor terminals could just mean the thermal fuse is open. Is the compressor real hot?" "Yes it is hot . . . But, not what I would call unusually hot." I had heard enough information to make a preliminary decision. "I won't condemn a compressor based on just an 'open'. Not yet. Do what you can to cool the compressor - Put a bag of ice on it. If it still shows open when the compressor is cool to the touch, I'll agree we need to replace the compressor. And . . . Mel, please confirm that the condenser fans are operable." "Yes, Sir. . ." About an hour later, Mel returned to the shop. "You were right, once the compressor cooled off, it came back on. It had overheated because one of the condenser fan motors had seized. The fan motor that runs whenever there is a call for cooling. Only two of the three condenser fans are on a capacity circuit. Two fans stage according to discharge pressure but one runs constantly. That is the one that seized. . . " I finished the sentence, " . . . and the compressor went out on thermal overload." "Yes", Mel nodded. "Well, at least a $119 condenser fan motor is a lot cheaper and easier to replace than a $3000 low-temp compressor!" Like Jerry used to tell me, "Basic troubleshooting starts with checking the basics." Doc 2005.08.06 |
