1990/02/12 Caterpillar

SUPPLEMENT: 03/05/90

SERVICE MAGAZINE; FEBRUARY 12, 1990; PAGE 17; "Contaminated Refrigerant Can Cause Air Conditioner Failures". The second-to-last paragraph contains erroneous information. The illustration and picture caption are also incorrect. The correct information follows.

Moisture detectors are now used on some models (see the illustration). The 7T5136 Indicator contains material that is blue when dry and turns pink or red in the presence of moisture. If the center (inner) portion is pink, the receiver/dryer should be replaced. The indicator can be added to other models where space permits.

Ring (A) is color-coded: "DRY" portion is blue; "WET" portion is pink. When moisture is detected in the system, the center portion (B) turns pink or red. When the indicator does not detect any moisture, the center portion is blue.

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Reference: Service Magazine; July 7, 1986; Page 15; "Larger Capacity Air Conditioner Receivers (Dryers) Available With Quick Disconnect Fittings".

Reference: Service Manual, SENR3334, "Air Conditioning And Heating Testing And Adjusting".

Air conditioning systems are equipped with a receiver/dryer, containing pellets of desiccant material which will absorb and retain moisture that may be present in the system.

1. It will combine with the refrigerant to form small amounts of acid, which is damaging to internal compressor parts.

2. It will cause rusting of steel parts, and rust particles can clog or damage the compressor and expansion valve.

3. It will cause oxidation of the refrigeration oil, creating sludge.

4. If there is more moisture than the desiccant can hold, the desiccant pellets will separate into a fine powder that will be distributed through the system, damaging the compressor and plugging the expansion valve. The powder is very difficult to remove from the system, and repeat failures may occur.

1. The user may leave the system open to atmosphere after hose failure or other damage.

2. When the system is charged, the required amount of vacuum may not have been applied, or it may not have been applied long enough. The purposes of applying the vacuum are:

a. To remove all traces of air from the system, and

b. To cause moisture that dissolved in the oil to come out of solution, vaporize, and be removed from the system.

3. Refrigerant oil may be added which has not been properly stored in an air-tight container, and moisture has become dissolved in the oil.

4. A very small amount of water will pass through the rubber hoses and into the refrigerant, due to osmosis. This occurs whether the machine is running or not, and varies with the humidity in the air.

How to minimize moisture in the system:

1. Observe correct evacuation and charging procedures.

2. Use only the specified refrigerant oil, stored in an air-tight container.

3. Repair promptly if a leak occurs.

4. It is recommended that the receiver/dryer be replaced:

a. Any time the system is opened for any reason, or

b. Once a year, regardless of machine operating hours.

Receiver/dryer replacement normally requires discharging, evacuation and recharging of the system. However, some models have quick-disconnect fittings on the receiver/dryers, permitting receiver/dryer replacement without discharging the system. This allows dryer replacement in a few minutes, without significant refrigerant loss. Receiver/dryers with quick-disconnect fittings can be added to other machines, if space permits; see reference article.

Moisture detectors are now used on some models (see the illustration). The 7T5136 Indicator contains a ring of material which is blue when dry, and turns pink or red in the presence of moisture. If the indicator ring is pink, the receiver/dryer should be replaced. The indicator can be added to other models where space permits.

Some dealers have added a dye solution to air conditioning systems to aid in finding leaks. This is NOT recommended. The dye solutions contain a vegetable dye which can turn into sludge, clogging the expansion valve and compressor. Use an electronic leak detector to locate leaks. The electronic detector is very sensitive and will work anywhere in the system. The dye solutions are not effective in the higher parts of the system where oil does not collect.

When moisture is detected within the system, the area labeled "WET" turns pink or red. When the indicator does not detect any moisture within the system, the area labeled "DRY" turns blue.