REFRIGERATION SYSTEM TROUBLESHOOTING

TM5-4120-347-14

5-15. REFRIGERATION SYSTEM TROUBLESHOOTING

The two most likely malfunction symptoms to be reported to direct support maintenance are: (1)

Unsatisfactory color or bubbles observed in the sight glass; and (2) reduced cooling capacity. Discussion with

operators and/or organizational maintenance personnel as to how the symptoms appeared can often be more

informative than the symptoms themselves.

a. Sight Glass Indications. There are two indications that may be observed in the sight glass; color as a

result of moisture content in the refrigerant, and vapor bubbles in the liquid refrigerant.

(1) Color Change. A bright green color indicates that the refrigerant is dry. As moisture content

increases, the color will fade through chartreuse hues until it reaches pure yellow. A gradual fading from green

into chartreuse over an extended period of time is normally an indication that the dehydrator is becoming

saturated with moisture. A sudden change of color is highly unlikely unless a rupture occurs allowing all

refrigerant to escape.

(2) Bubbles. The appearance of an occasional bubble in the sight glass can be expected, especially

when operating in a high ambient temperature. A gradual increase in the number of frequency of bubbles is

usually an indication that the refrigerant charge is being lost from the system through a small leak. The number

and frequency of bubbles will also increase if the refrigeration system becomes over-heated. The sudden

appearance of numerous bubbles is usually an indication of a serious leak.

b. Reduction in cooling Capacity. A reduction in cooling capacity will occur as a natural result if refrigerant

is lost from the system; with a total loss of cooling if all refrigerant is lost. However, a considerable proportion

of the refrigerant may be lost before the reduced cooling capacity is noticeable. Sudden or erratic reduction, or

complete loss, of cooling capacity is often caused by the malfunction of one of the valves in the refrigeration

system. Cooling capacity will also be reduced if the refrigeration system becomes overheated.

Overheating of the refrigeration system is often the cause of bubbles appearing in the sight glass, or a

reduction in cooling capacity. Adequate cooling of the hot, compressed refrigerant vapor in the condenser is

essential to the proper operation of the air conditioner. The following checks should be made to ensure that

overheating is not the cause of the symptoms before troubleshooting the pressurized portion of the

refrigeration system:

a. Be sure there is no external obstruction to the air flow into the condenser intake screen and out of the

condenser fan guard.

b. Be sure there is no obstruction within the intake screen and fan guard.

c. Be sure there are no obstructions or an excessive build-up of dust and dirt in the condenser coil

Except in cases where it is obvious that the refrigerant charge has been lost, the first step in troubleshooting

problems in the refrigeration system should be to check discharge and suction pressures under operating

conditions. Check pressures as follows:

a. Turn the mode selector switch to OFF.

b. Remove the charging valve access cover.

c. Connect individual pressure gages or a refrigeration servicing manifold and hoses to the high

(discharge) and low (suction) charging (service) valves.

Open the low (suction) and high (discharge) charging valves.

Both gages should read the same. Check the reading with the appropriate column in Table 5-1. If the

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