Manitowoc Q series flaker

[Servicerunner]

Hello,

This is my first post on this forum but I think i've read every post in the refrigeration and ice making forum and let me just say there is a lot of knowledge here and this forum has basically made things much easier for me at work. I'm work part time for a refrigeration company and am in school at community college for commercial refrigeration and hvac.
I have serviced the following machine 3x in the past 2 weeks, not exactly sure what is happening. It is a Manitowoc QF0800A. It is an air cooled model. The first customer call was for "no ice". I took the front cover off and the led for "Discharge Temp" was blinking. The condenser was slightly dirty, I blew it out with nitro and cleaned with coil cleaner, I cleaned it really well. I thought I was done and got a call back "no ice machine shut down". I went back and the discharge temp light was on again. I got the manual, I checked the operation of the discharge thermister--it was mounted correctly on the discharge line and was reading right (i checked it with my own thermister insulated and clamped to discharge line at same location). I ohmed the ice machine thermister across a range of temps and the thermister was dead nuts on. Superheat is about 18 degrees, subcooling about 4 degrees--404a. Suction pressure is 5 pounds, head pressure ranges, fan cuts in at 245 and cuts out at about 210. I've read other posts on this forum and some people have jumped out the thermister with a resister of a certain value to trick the board, i'm considering that. But I wonder why it worked ok for so long and then gets this fault. I'm thinking of replacing the fan cycling control because I'm wondering if it isn't just maybe failing once in a while and tripping that thermister. Although I ran the machine for about 1 hour and temps were getting about 200 degrees on discharge line (thermister will stop operation at 245 for a set period of time also cuts out on low temp for a set period of time, but low temp hasn't been an issue). The area the machine is in is conditioned and stays about the same temp year around. Maybe I should jump out the fan cycling control what do you guys think Thanks

[itsiceman]

If inside a conditioned space the low suction coupled with the fan cycling would make me want to know more about the amount of refrigerant in the system. I wouldn't remove the thermistor. Sounds like it is working like it should to protect the compressor

[itsiceman]

(thermister will stop operation at 245 for a set period of time also cuts out on low temp for a set period of time, but low temp hasn't been an issue). The area the machine is in is conditioned and stays about the same temp year around. Maybe I should jump out the fan cycling control what do you guys think Thanks

Sorry read this again a saw this. While the compressor is running the unit might not trip a low temp. safety....... a compressor shut down on thermal overload would have a lower than normal discharge line temp though.

[icemeister]

That 5 psig suction pressure is way low and is likely causing the high discharge temperatures, so I'd say it's low on refrigerant.

[itsiceman]

That 5 psig suction pressure is way low and is likely causing the high discharge temperatures, so I'd say it's low on refrigerant.

Ok he has been there three times in a row so I guess its not time to beat around the bush

[Servicerunner]

That 5 psig suction pressure is way low and is likely causing the high discharge temperatures, so I'd say it's low on refrigerant.

Manitowoc lists 10 psig as the normal low side operating pressure, I guess that I've been told so many times that leaks are unusual with ice machines I didn't consider a leak.
One other thing, is that the water in this area is very hard and contains a lot of minerals. There is an ecolab filter on the ice machine, but I can't verify how well it functions. And I'm not sure about the cleaning of the machine because the owner does that. If you had a limed up evap, could that be causing the 5 psig suction and high superheat? Maybe that would explain the normal subcooling numbers AND high superheat?

[itsiceman]

Low load
Low pressure
Low superheat

Low charge
Low pressure
High superheat

[Tommy knocker]

Low load
Low pressure
Low superheat

Low charge
Low pressure
High superheat

Bingo. Leak test time. IMHO.

[itsiceman]

Manitowoc lists 10 psig as the normal low side operating pressure

With 70˚F air it shows 18-22psi in my book

[Servicerunner]

With 70˚F air it shows 18-22psi in my book

Could you point me to that online? I originally found my info on the manitowoc website while on my phone and can't seem to find the same document. Thanks for everyone's help, I really should have considered low charge more... oh well still learning.

[Gunslinger]

Ice machines have had leaks...check for rusted drier.

[itsiceman]

Could you point me to that online? I originally found my info on the manitowoc website while on my phone and can't seem to find the same document. Thanks for everyone's help, I really should have considered low charge more... oh well still learning.

Try this link and welcome to the site SR

http://www.manitowocice.com/asset/?id=ceeav

[Servicerunner]

Try this link and welcome to the site SR

http://www.manitowocice.com/asset/?id=ceeav

Don't know what I was thinking (it had been a long day) that manual actually says at 70 degree ambient suction should be 33-37 psig. Which would give me an evap of about 0-5 degrees, which (and correct me if i'm wrong) is about where an ice machine should be. Only thing I don't understand is why I'm getting good/normal subcooling numbers? If I have a low charge I'd expect subcooling to be off as well. From all the posts i've read here i think I should thouroughly clean using the "heavily scaled" procedure...then see what kind of numbers I get?

[itsiceman]

I don't see those numbers either SR.
You must be reading a S model somewhere and not the Q# you posted
They don't publish the SC numbers but 4 imo is low also.
You can't go wrong by cleaning it too............ unless you use the wrong cleaner

[Servicerunner]

I don't see those numbers either SR.
You must be reading a S model somewhere and not the Q# you posted

You're exactly right, I was reading another model's operating pressure. Your original post was correct, I should be at 18-22...which gives me an evap of about -20.

I'll try cleaning and report back....

[Servicerunner]

Just wanted to also say Itsiceman I really appreciate your help, I'm learning a ton, love this forum!

[itsiceman]

I'll try cleaning and report back....

Bring leak detector some gas and a scale too

[Grayline]

If it were my call I would get the machine as close back to square one as possible, super clean condenser,descale,recover.refrigerant weigh in-out then acess possibilities.I have had the situation where all is perfect until night time the customer has a new mgr. They turn the A/C off or back at close and the machine bakes in its own heat.causing to throw a code and shutting down by the time service tech gets there the A/C is back on and all seems normal. Also add in the diagnosis of hot or warm water entering the machine. That coupled with dirty condenser and or overcharge would trip a high temp alarm. Just keep in mind the fan cycle is there to help aid the higher head pressure needed for adequate "heat" for harvest in a cuber not in a shaver.