Hoshizaki KM-500 MAE short freeze cycle
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  1. #1
    Join Date
    Nov 2005
    Location
    Venezuela
    Posts
    30

    Hoshizaki KM-500 MAE short freeze cycle

    Hi everyone. It's been a couple of months since I've logged in. I hope you're all well and making plenty of money.

    I have a Hoshizaki KM-500-MAE icemaker in the shop that's going into the harvest cycle right after the 5-minute lock out. Normally that would be a water problem or a float switch problem, but not this time.

    I've got plenty of water, the float switch is brand new (and works), the pump and capacitor are brand new (and work) and the thermistor resistance matches the resistance chart in the manual.

    Everything else on the machine is doing what is should, so I have to suspect the control board.

    Does anyone have a better idea before I tell the customer the bad news?

    Greeting from Venezuela, especially to Ice-meister.

  2. #2
    Join Date
    Mar 2007
    Location
    Toronto
    Posts
    259
    You could check the air holes at the top and the bottom intake to the float switch. It could well be the board though I've never had this particular problem with the board. I try to carry a new board for all the major ice machines so I can quickly eliminate the board as the problem. The other thing is whether the switch on the board is on Alpine or C. If the main power 10 lead cord has a white at the end it is a C board. If there is no white it is an Alpine. Maybe that Orinoco water is just ornery.

  3. #3
    I'm sure you've checked all that basics. Did you sequence the improved E board by the test switch 2,3,4,1 ? Smells like a freeze timer problem on that board.
    FEN

  4. #4
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,249
    Pull the float switch connector and put a jumper across the board terminals. If the machine goes into harvest immediately after the lockout, it ain't the float switch......it's the board.

  5. #5
    Join Date
    Nov 2005
    Location
    Venezuela
    Posts
    30

    Mojo and DoctorIce

    Thanks, guys.
    It's an Alpine board on a oldish machine. Ran through the board diagnosis in the manual, and everything checks out fine.
    Parts for icemakers are expensive and hard to get here, so I don't carry a spare board, though it makes a lot of sense. I'll have to send to the U.S. for a new board if that turns out to be the problem.
    Whatever machine I'm working on, I always pray it's not the control board failure. I can repair most of the electromechanical parts, or replace them with something similar, but the boards are a big problem.
    I've rebuilt machines, replacing the electronics with electromechanical parts, or using stuff like the Danfoss controllers, but Hoshizaki logic is a bit tougher to simulate.
    I'll check out those air holes, Doc. And the Orinoco water, too. Maybe there's a Piranha fish stuck in the float switch.

    Best wishes from Venezuela.

  6. #6
    Join Date
    Nov 2005
    Location
    Venezuela
    Posts
    30

    Hi Icemeister...

    "Pull the float switch connector and put a jumper across the board terminals."
    Did that first. It's not the float switch, I'm pretty sure of that. Anyway it's brand new. Thanks for the suggestion, though.

    On another subject, the icemaker project we talked about a couple of months ago is still alive. Found someone to make the evaporators for me. Learned how to calculate the heat load and size the compressor (thanks to your tips and links). Designed the control system. Now to design the casing, get the bits put together, and build the prototype. I'd like to have one made by Christmas. I'll keep you posted.

    Best wishes from Venezuela.

  7. #7
    Join Date
    Apr 2004
    Location
    Charlotte, NC
    Posts
    648
    Quote Originally Posted by mister frío View Post
    "Pull the float switch connector and put a jumper across the board terminals."
    Did that first. It's not the float switch, I'm pretty sure of that. Anyway it's brand new. Thanks for the suggestion, though.

    On another subject, the icemaker project we talked about a couple of months ago is still alive. Found someone to make the evaporators for me. Learned how to calculate the heat load and size the compressor (thanks to your tips and links). Designed the control system. Now to design the casing, get the bits put together, and build the prototype. I'd like to have one made by Christmas. I'll keep you posted.

    Best wishes from Venezuela.
    Just a thought, but, if you have plenty of water and the float is good, check the check valve for the drain. They are the triangle shaped plastic part the pump has a tube going to. You have one inlet tube for the pump and two outlets. One outlet sends water through the top section for evaporator and the other sends it down the drain when the pump is reversed. When the check valve is partially held open the water will be forced down the drain causing the float to break and call for fill. When that unit calls for the second fill it goes into harvest. Just a thought.........
    "Fighting Ignorance since 1973 (It’s taking longer than we thought)." The Straight Dope.

  8. #8
    Join Date
    Nov 2005
    Location
    Venezuela
    Posts
    30

    Thanks, Ckone180...

    "When that unit calls for the second fill it goes into harvest. Just a thought..."
    I've had a few headaches with this particular machine, and that was one of them. For starters, the new pump would only run in "reverse", and would pump the machine dry within a couple of minutes of starting the freeze cycle. I didn't notice it at first, but when I did I assumed it was the check valve leaking. The spring looked fine, but I stretched it a little, anyway. Spring seating is fine, and the rubber seal is in good condition.

    There followed a period of two hours when I thought several times about hitting the damn thing, because the pump wouldn't run forwards to circulate the water. I tried several "experiments" to get it to to run both ways before I discovered that it was a defective capacitor. First time I've come across that problem. Anyway, it was now solved, and it runs backwards AND forwards just fine, with no leaks from the check valve.

    So now there's plenty of water in the tank when the machine goes into the harvest cycle after the 5-minute lock-out. I checked that the float switch was closed, too, as I suspected it might be sticking open and faking an empty tank.

    Despite the board diagnostics checking out OK, it's sounding more and more like an electronics problem, isn't it.

    The only other obvious thing that I need to get to eventually is a higher-than-usual suction pressure. With 90ºF air and 75ºF water I'm starting the freeze cycle with 72 PSI and 250 PSI discharge. I suspect that the hot gas bypass is leaking, but I can't see how that might affect the switchover to harvest after the first 5 minutes.

    Thanks from Venezuela.

  9. #9
    Join Date
    Jul 2007
    Location
    alexandria va
    Posts
    138
    hoshis dont have a second fill. if u jump the float and it still goes in at 5 min order u a board. also check txv bulb clamps. they are problably rusted with would explain your high suction. peace out jbb

  10. #10
    Join Date
    Nov 2005
    Location
    Venezuela
    Posts
    30

    Thanks, JTRefrig...

    I'll check out those clamps. Good advice.

    Greetings from Venezuela.

  11. #11
    Join Date
    Mar 2007
    Location
    Toronto
    Posts
    259
    I have a fair number of used Alpine boards. I prefer them to the new board when the machine starts having harvest problems. Could I send you a used board (checked out of course) without causing a lot of customs problems?
    I'll send it for free but should I put a value on it?

  12. #12
    Join Date
    Nov 2005
    Location
    Venezuela
    Posts
    30

    Thanks, DoctorIce....

    ...that's a really generous offer. If you were a bit closer I would gladly accept, but there are a few snags with sending anything:

    1. We don't have a regular mail service worth the name. My sister in the UK regularly sends me stuff, and only about 50% of it gets here, and the other 50% takes up to six months and a great deal of sleuthing to get hold of. So if it's anything important she has to use FedEx or similar.
    2. The cost of your shipping a board to Venezuela via FedEx would probably be pretty high, and I'd hate to put you to that expense.

    When I order parts from the U.S. I have to specify courier delivery and pay extra. That hurts, because we have strict currency control here, and I have to buy US dollars on the black market at double the real value.

    However, it's great to know that there's a helpful guy like you up there in Canada. If you're ever down in my neck of the woods, count on somewhere to stay. As they say down here, "Mi casa es tu casa".

  13. #13
    Join Date
    Nov 2005
    Location
    Venezuela
    Posts
    30

    Hoshizaki update...

    This machine is going to drive me crazy! Today I got so fed up with it I pulled out the control card and all the wiring. I checked every single component on the machine, right down to the on/off switch. On a workbench I wired up the transformer to the board, and ran the diagnosis cycles again with plenty of room to watch what happened. I put the tester across the 4 relays and watched them open and close, as well as checking the pin continuity on K1.

    The only out-of-the-ordinary thing was that the (downloaded from Hoshizaki) manual indicates that there are FIVE relay/pin checks, activated by bridging the float switch terminals FIVE times. But on this board, the relays cycle after FOUR bridges, omitting the second bridge shown in the manual. Perhaps it's an updated manual and I have an out-of-date board.

    Anyway... Close to 6 p.m. satisfied that everything else worked just fine, I rewired the machine (somewhat tidier than before), fired it up and was surprised that it ran a full cycle perfectly normally! I only ran one cycle because it was getting late.

    Now I have another problem, if the machine works just fine tomorrow. I didn't actually "fix" anything, it just started working. I'll have to keep it running in the shop for at least another week before I can return it to the customer with any degree of confidence.

    Maybe it was just a loose connection, but I'd sure like to know which one!

    I'll keep you posted on tomorrow's results.

    Thanks guys. Greetings from Venezuela.

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