TM 55-203
(5) Close the receiver shutoff valve and
obtained when a pressure of 10 to 15 pounds per belt,
pump the system down until the low-pressure gage shows
applied midway between the compressor and motor
a slight vacuum.
pulleys, will depress a single belt 1 inch. More sag than
(6) Open the oil filling valve slightly and
this shows too little tension and will cause belt slippage
permit oil to enter.
Greater tension increases belt stretch and shortens
(7) From observation of the true oil level,
wearing life. The faces of the compressor and motor
estimate the quantity of oil required to fill the level to
pulleys should be in alinement Check this after belt
within 1/8 inch of the top of the sight gage and admit only
adjustments The face of the motor pulley must not project
this amount.
out past the plane of the face of the compressor pulley
(8) If the true level cannot be determined
and should not be more than 1/16 inch behind this plane.
because of being below the sight gage, admit 2 pints at a
time, operating the equipment after each addition until the
e. Lubrication. The compressor flywheel bearing is
level can be determined. Then proceed as outlined
wick-fed lubricated from an oil reservoir in the crankcase
above, falling to the desired level.
under the bearing. This reservoir should be drained,
(9) Close the oil filling valve and replace the
flushed, and refilled monthly while air conditioning is in
plug in the valve outlet; open the receiver shutoff valve.
use. Access to the reservoir is through oil filling plugs on
each side and in the bottom. The reservoir holds one-
Caution: Never let the oil level in the container
fourth inch and should be filled to the level of the filling
hole. All other lubricated surfaces are fed from the oil
fall below the mouth of the tube when adding oil, as
pump in the compressor crankcase. The crankcase holds
this would allow the compressor to suck in air.
12 pints of oil, filled to one-eighth inch from the top of the
sight gage. The oil level must be checked after one-half
g. Refrigerant Troubleshooting. The diagnosis of
hour of normal operation and immediately upon shutting
trouble in the refrigerating system is a problem of cause
off the compressor. The accumulation of Freon in the
and effect. The troubleshooter must have accurate gages
crankcase when the equipment is idle results in a fictitious
and thermometers, otherwise misleading reading will be
oil level indication. This may cause violet boiling of the
taken. Care must be taken in handling Freon since it has
crankcase mixture when the pressure is reduced while
no odor and gives no warning of leaks. Car repairmen
pumping down This result in oil being carried into the
must wear goggles when working on parts from which
cylinder and pumped into the system, lowering the oil
refrigerant may be liberated. If liquid refrigerant (Freon)
level in the crankcase. The need for operating the
gets into the eyes, the injured person should be rushed to
equipment for some time before obtaining the true oil
a medical officer for attention. The following procedure is
level is obvious. Oil must be added when the observed
prescribed in the interest of safety:
true level is within 1/8 inch of the bottom of the sight
gage.
(1) Open the compressor control switch
before starting work around the electrical parts or rotating
f. Refilling Crankcase. To add oil to the crankcase,
parts.
proceed as follows (compressor crankcase oil should be
(2) When the refrigerant vapor is pumped
kept in, clean closed containers and not be left open to
from the compressor crankcase, follow the intermittent
the atmosphere any more than absolutely necessary):
operation to avoid pumping over excess amounts of oil,
and building up of pressure in the crankcase. This
(1) Place sufficient quantity of #24 or #25
pressure is caused by the release of refrigerant dissolved
refrigerating machine oil in a clean container.
in the oil and results in blowing out of refrigerant vapor
(2) Remove the plug from the oil charging
and oil when the crankcase is opened.
valve on the side of the crankcase.
(3) Permit the evaporator unit to warm up to
(3) Screw a short nipple into the plug hole
room temperature before pumping down the refrigerant.
and attach a clean rubber hose or copper tube to the
This precludes escape of any liquid refrigerant left when
nipple.
the evaporator is disconnected.
(4) Submerge the fuel end of the hose (or
(4) Check the oil level in the compressor after
tube) well down into the oil in the container and open the
replacing major parts, which may contain
valve very slightly to purge the hose.
12-3
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