Non Working Bunn U3
I picked up an old used U3 the other day from someone that took it out of a racetrack or something. Didnt know if it worked. Got it cleaned up & today I started trying to get it working. Main problem is turning it on & turning up the thermostat & the contactor starts yelling. Ive tested the voltage coming in, the limit thermostat, the contol thermostat & everything seems to be working fine. Continuity is fine on the control thermostat & contactor. I even bypassed the control thermostat & still had the yelling. So Im assuming the contactor is maybe blown & its fine when the thermostat is set to off & the continuity is fine but when its under a load it doesnt work. But would there be anything else causing this? I havent determined that the heating elements are working (about to try bypassing the contactor & see if the heating element at least acts like its working). Anyone have any insight? I had this same problem on a previous machine about 6 years ago but I cannot remember the fix. Cant remember if I replaced the contactor or something else. I know I've replaced plenty of limit thermostats & control thermostats on Bunn coffee makers & heating elements on different espresso machines & coffee makers but I cannot remember what I did to fix this contactor yelling.
Replies to This Discussion
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Permalink Reply by Mitch Buckner - Bella Caffe on
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I guess noone in the group has any ideas on whats wrong with this machine. I've got to brew 30 gallons of coffee next week, guess I'll be doing it with my 3 bunn pourovers!!!
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Permalink Reply by luke hudek on
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I don't know if it will help any, but can you snap and post some shots of the inside where you feel the problem is?
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Permalink Reply by Mike Sabol on
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What do you mean by "yelling"? Have you taken a RESISTANCE reading on the elements? Are the points dirty on the contactor? If you have 208 going into the contactor is there 208 coming back out? What is the voltage going accross the coil on the contactor? 120? 0? 208? 43? What is the coil on the contactor rated for? Where does the contactor get the power from? Have you traced good voltage from the wall to the contactor via all the intermediary safety devices? If you manually activate the contactor does it still "yell"? Have you replaced the contactor with a new one and had the problem go away?
I bet the coil on the contactor is fried. But get a resistance reading from the elements before you go buying anything. Get the resistance reading and then do the Ohm's Law calculation and make sure the elements are kosher. Maybe somebody put in 120v elements and they are pulling a shitload of current and freaking out the contactor. My advice as a field tech is to always take a resistance reading on elements. Any element. All the time. It is never wasted time, it's good information, and if you find a 23 MOhm element you just saved yourself 4 hours of troubleshooting.
What about the fill circuit? Maybe the contactor is freaking out because the LLB (or whatever is contoling the fill level) is thinking full-not full-full-not full-full-not full.......and cycling the coil. And speaking of the coil, what is the resistance on the contactor coil? That coil is going to be rated for either 120v or 208-240v. Take a resistance reading and do the Ohm's law calculations. Does the coil exhibit 0 Ohms or perhaps 340 KOhms? You want to find an ohm reading that is sane for what it's rated.
I don't know the U3 specificaly but I know that Bunn machines often run without a fill/safety circuit in place. So is the unit full of water when you apply the juice? With coffee equipment always hook up the water first. Always. That yelling could be the elements heating dry, which will happen with Bunns if you're not careful. And that would be a BAD thing.
Now go and get some resistance readings and tell me what you find.
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I did a resistance reading on the heating elements & each came up right around 20. My meter can only be set to 2000ohm or 200kOhm. the wattage for the machine is 6725 & its a 240V. I have checked all the voltage coming in to the machine & coming into the contactor. All of this was done about 2 weeks ago. I've been out of town since then so Im going off memory. Doing readings on power didnt seem to find anything off. Its getting the right power it just wont send power to the heating elements which makes me think the contactor is fried (although it seems like I wasnt getting that impression from simply taking readings). Basically the machine powers up, water pump cuts on, water fills up (it also overflowed but I think that may have been because it wasnt completely level). Push the button & water pumps out of the brew spout (just not hot). The only thing that isnt working correctly is when the thermostat is turned up, it wont turn on the heating element (and the contactor is yelling horribly, I could hear it from outside when I flipped the breaker back on!)
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You should get a new contactor. At least that will stop the "yelling". I still bet the coil on the contactor is bad.
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