harvest problem

[jgjn]

Working on manitowoc B 250 water cooled ice machince. Makes ice in freeze cycle,goes into defrost but ice does not drop.Put level on machine and tilted to front just little. Ice pattern looks good, hot gas valve is opening at least a litte because line at bottom of evap.plate is warming up. Can a dirty evaporator plate cause this problem ? Although it looks ok. Or can the hot gas valve not open all the way ? Can I check valve by measuring temp on both sides of valve ? Didn't have much time today to really check out going back tomarrow morning.

[skorch]

need more info. does ice melt away? is ice thickness correct? does ice continue to build up? explain what is happening.

[jgjn]

It will try to go into harvest. But ice will not come off evaporator plate. After being in defrost for 3 minutes it will finally kick back into freeze cycle. Ice thickness probes will then send it back ito defrost mode. It will do this 3 times before it goes into lockout and give code of 3 harvests over 3 minutes. Sometimes I am told the ice will drop on the second try of defrost. Ice thickness is good and probes are working or it would not go into defrost.

[Edited by jgjn on 12-14-2004 at 10:45 PM]

[skorch]

clean evap with proper chemical. sounds like eveap coil dirty.

[R12rules]

Do what the guy above me said.

Plus replace the thickness probe. Cheap insurance. Make sure you adjust the probe correctly.

Also, get in there real close and inspect the plate to make sure no one has used to hammer and screwdriver to "assist" the harvest.

Little nicks in the surface of the plate show vandelism. Bad news.


There is other stuff to look out for also.

While your at the deal buying that probe, get the small book on the machine. AND some nickel safe ice machine cleaner.

Your on the right track though.

[shaka]

First of all you need a book.

You can not tell if the plate is limed up if its wet. clean it first like skoch and R12 said.

Making the ice is the easy part. Harvesting the ice is more critical in my eyes.

You actually have to generate enough heat for harvest, the discharge line must reach 160 deg. before harvest or you dont have enough heat to drop the ice.

If you dont reach 160 then you might have problem with superheat.(txv bulb loose or not insulated)

You need a book because it could be anything.

Dont install your long hvac gauges. Dont install any unless you know for sure its a refrigeration problem. If you already have then now you are low on freon.

you need more freon to harvest ice than to frezze it. Slighty low could cause longer harvest.

[rimek]

Check the weep holes in the back of the plate-should be clear. Use a nickel-safe delimer to clean plate -Calgon has one. How old is this machine? Manitowoc had some problems with warping a while back, and the make a cube gauge to check the individual cells. Also if there is any missing nickel plating, that also will grab. Can you pull the ice plate away from the evaporator? What is the bridge thickness when you try for the first harvest?-should be 3/16". What is the refrigerant and the head pressure? What is the condenser water outlet temp? The bridge sensor is probably fine- if the bridge is not too thick, that problem is usually a short(always harvesting) or an open(never harvesting).

[tbk]

also make sure your cond fan is shutting off in the defrost mode, b models are famous for the SCR delay timer to short and backfeed voltage to fan!!

[skorch]

you defenitly are getting expert help from the other guys. don't forget to time the defrost cycle. had one where the time was way short- turned out to be a bad circuit board.

[icemeister]

Clean the evaporator with a good nickel-safe acid cleaner. If the evaporator surface isn't shiny clean like nickel should be, isn't slick and smooth like it should be your evaporator and therefore your machine is toast. Don't waste your time.

It's a B-Series. It has to be ten years old or so. It's lived its life. Let it go.

[limpellizzeri]

I think the key to this problem is the water regulating valve. Is it shutting off tight during the defrost or is there a small trikle of water thru the condenser causing the head pressure to be too low and losing the needed heat for a proper defrost. Check the water regulating valve I bet it is leaking thru.

[dadofv]

look behind plate for seperation of tubing, or check seals on sides if it has them and if not make sure you are not forming ice through the sides and holding the plate.

[jgjn]

Thanks for all the reply's. I have the book on the manitowoc machines. But with all the years of accumulated knowledge on this site I just posted thread. And I wasn't disappointed. It was the water regulating valve. Didn't have enough head pressure to properly harvest ice. Thanks again for the help.

[gastech]

Chk for tube separation on back side of plate. Thicken up the slab. Replace machine.

[dum one]

clean the machine and it will be ok. it may sound simple but dont over think your problem.the rest of the suggestions are great, but realy too much for this problem.

[s-cube]

Sometimes the horizontal grids break loose on the evaporator plate. This causes the ice slab to hang on. There is no repair, however you can use a pair of pliers to pull the loose grid completely off. The machine will still make ice, just with a few extra large cubes. B model...at least ten years old...time for a new one.

[R12rules]

Originally posted by shaka
If you dont reach 160 then you might have problem with superheat.(txv bulb loose or not insulated)

Dont install your long hvac gauges. Dont install any unless you know for sure its a refrigeration problem. If you already have then now you are low on freon.

I agree yo need the head pressure during harvest. But what is this about NOT installing your gages until you are sure it is a sealed system issue?

Why would simply installing the gages make such a profound difference in system charge?

And what is the diference between using his long hoses and using a pair of short hoses? How would this affect his readings?

[indian]

I'd tend to agree about not hooking up the gauges until later. I went to a Manitwoc school and the rep insisted the first thing to do is whip out the book, that was a few years back, and as it turns out he is right.
Self contained (no remote condenser) systems are critical charge. If system is acessed on every service the unit will indeed someday be low on charge. If you're the last dude in line and find it low now we are looking for a non-existing leak.

[R12rules]

Oh Brave one, I agree you should bring out the book before you do anything else.
I agree you should not put on the gages unless you believe there to be a sealed system problem.

But the point I am after is the thing about your hoses.


Is anyone saying that just because you attach your gage manifold set ... you are disrupting the charge?

And if so, how much are you upsetting the charge?


I know the reason behind this proceedure. But not everyone does. And it is for their benefit we can shed some light onthe topic.
Besides, Dave's bored and wants stuff to talk about.

Not that he would "lower" his-self to discussing such puny systems as self contained ice makers ....(snicker, snicker)

[indian]

Well let's see, um, long hoses. Pressure drop, disturbing system equalibrium, flashing refrigerant, time required for system to normalize.

Don't make me go out to the service van to get the book please. The van is a mess and I will fell compelled to take care of some much needed house keeping.