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DIAGNOSING AIR-COOLED CONDENSING UNITS

Harvest Cycle

The headmaster control valve diverts the compressor

discharge gas to the ice machine receiver in the

harvest cycle. All refrigerant flow through the

condenser in the harvest cycle stops. Symptoms of a

headmaster valve that will not seat 100% closed

(completely bypass the condenser) in the harvest

cycle are:

 Freeze cycle suction and discharge pressure are

normal.

 The control board indicates safety limit #2. The

failure seems to be temperature related. Example:

The ice machine may function correctly at

temperatures above 32°F but fails at temperatures

below 32°F.

 Harvest cycle suction pressure is low.

 Harvest cycle discharge pressure is normal or

slightly low.

Procedure

1. Freeze cycle operation must be normal before

diagnosing the headmaster in the harvest cycle.

(Refer to Cycle Times/24 hr Ice Production/

Refrigerant Pressure Chart)

2. Allow the ice machine to run a normal freeze cycle

(do not initiate an early harvest cycle).

3. At the start of the harvest cycle feel the compressor

discharge line and the liquid line to the ice machine

receiver at the headmaster valve. The temperature

of both lines will be highest at the beginning of the

harvest cycle and then decrease. Compare the

lines for the first 30 seconds of the harvest cycle

and then refer to Harvest Cycle Headmaster

Control Valve Failure List.

Manitowoc QY0674C User Manual

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