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10TA Service Manual

SERVICE OPERATIONS

4/28/14

9-14

! WARNING !

It is not recommended that refrigerant be transferred from a

refrigeration system into a cylinder. If such a transfer is made,

the refrigerant cylinder must be an approved CLEAN cylinder--

free of any contaminants or foreign materials--and must be

weighed continuously to assure contents do not exceed net weight

specified by cylinder manufacturer or any applicable

code requirements.
! WARNING !

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.

Low line voltage.  A compressor motor is designed to operate within the range of plus or minus
10% of its nameplate voltage.  Low 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.

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.

High head pressure. The system is designed to operate at 200 psig. Excessive head pressure
adds refrigerating load on the compressor that can cause the windings to overheat and result in a
failure or burnout.

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.

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.