Vogt HEC-10, Service Manual

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HEC-Series Service Manual
SERVICE OPERATIONS
10/21/01
9-18
Refrigerant Leaks. In addition to testing the machine for leaks as instructed under “Refrigerant
Charge”, it is advisable to again make a leak test after the unit has been in operation approximately
one week. Any noticeable change in operating conditions, other than shown on the “Certificate of
Test” may indicate a loss of refrigerant due to a leak. Always remove the refrigerant pressure from
the vessel or tubing before repairs are attempted.
Non-condensable Gases. Satisfactory operation of the machine is not possible if non-condensable
gases (usually air) are present in the system. Excessive condensing pressure is an indication of such
gases. Excessive condensing pressure in water cooled condensers may also be due to the
accumulation of scale in the cooling coil or due to insufficient cooling water or excessive water
temperature. See “Water Cooled Condensers”, Section 7.
Compressor Motor Burnout. There are several causes of compressor motor burnout. Some of
these are described below.
1. Low Line Voltage. A compressor motor is designed to operate within the range of plus or minus
10% of its nameplate voltage. Low voltage or excessively high voltage requires the motor
windings to carry more current at the same compressor load. When this current gets too high or
is applied for an extended period, the motor windings overheat, resulting in a failure or burnout.
2. Loss of Refrigerant. The hermetic compressor motor is maintained at proper operating
temperature by passing cool suction gas over the motor windings. A loss of refrigerant can cause
the winding to overheat resulting in a failure or burnout.
3. High Head Pressure. The system is designed to operate at 200 psig. Excessive head pressure
adds refrigerating load on the compressor which can cause the windings to overheat and result in
a failure or burnout.
4. Moisture. Moisture in contact with refrigerant oil and the presence of heat will form hydrochloric
or hydrofluoric acid. The acid will destroy the insulation on the motor winding causing a short
circuit which can increase motor temperature in excess of 3000
°
F. This extreme temperature will
also create a sludge or black residue in the system.
5. Mechanical Failure. Mechanical failure has been determined as a major cause of motor burnout.
Bearing wear or wipe-out may allow rotor to drag--overheating the windings and burnout.
Whenever there is a compressor failure due to a motor burnout, it is important that the system be
thoroughly cleaned before replacing the damaged compressor or otherwise the new compressor may
also be damaged. A suction line filter should be installed and filter cores replaced until system is
cleaned. Also replace the liquid line filter drier.