Manitowac QM30

[apprentice3]

I have never worked on any ice machine until the other day. On this ice machine, in the book it says the freeze cycle + harvest cycle length is determined by the Liquid Line Thermistor. I was wondering what kind of temps. this thermistor sees in order to stop the freeze cycle, does the liquid line start to cool down and it intiates harvest? Also this particular Ice Machine had a leak on the suction line, so it was low on refrigerant, and it would make like 1 ice cube, my question is your superheat is high/suction line temp. high, why would the unit ever go into harvest?

[DoctorIce]

There are not many QM30 machines in the field as most customers will buy the Whirlpool 50# cuber for half the price. I have only one customer with this machine and the evaporator went after 4 1/2 years (only a 3 year warranty on the evaporator on this model. The control board is different than other Manitowocs (a lot simpler) but there may be an 1 hour cut-out safety for freeze like normal Manitowoc machines. Anyway the factory technical help line is 1-800-545-5720

[Tech Rob]

The QM30's thermistor produces a higher resistance as the liquid line temperature drops. What initiates harvest is the ice thickness dial on the control board. The length of the freeze cycle is determined by the setting of the dial, as the control board "reads" the resistance of the sensor.

Did you personally confirm and repair the leak in the suction line? Did you weigh the charge back into the system per specs? A dirty evaporator would not affect the liquid line temperature right away, but would lead give you high superheat/suction.

[apprentice3]

Yes i confirmed leak in suction line. A dirty evaporator would cause high superheat/suction? I would think Low superheat Low suction, because to me if the evap. was dirty the refrigerant couldnt pick up heat from the water, thus leaving refrigerant cooler and not superheated.

[Tech Rob]

Oops.

The QM30 uses a cap tube metering device, right? If that's the case, you're correct.

Sorry.

[apprentice3]

Yes it is a cap. tube, What metering device were you thinking of?

[Tech Rob]

thermostatic expansion valve.

I'm curious, though... Where were you measuring superheat? Before or after the heat exchanger?

[jonbailey19808]

For the QM30 there is a guide for diagnosing it by tempertures in the under tech handbook.

Dont know if you got this one done yet. If its still an issue let me know.