Air Conditioning and Heating R-12 All Caterpillar Machines – Refrigerant Orifice Tube System



Illustration 1 g00647547

Typical Refrigerant Orifice Tube System

(1) Compressor

(2) Condenser coil

(3) In-Line dryer

(4) Evaporator coil

(5) Accumulator

(A) Refrigerant is shown as a gas with high pressure and high temperature.

(B) Refrigerant is shown as a liquid with high pressure and high temperature.

(C) Refrigerant is shown as a low pressure and low temperature liquid.

(D) Refrigerant is shown as a gas with low pressure and low temperature.

Note: In an orifice tube system that is properly charged, frost may form between the orifice tube and the compressor. The frost may be present if the system is operating properly and if the system is properly charged.

Note: In an orifice tube system, a combination of abnormal pressure and frost MAY indicate blockage in the system.



Illustration 2 g00647550

Typical In-Line Dryer

(6) Quick coupler

(7) Orifice tube assembly

(8) Desiccant

The orifice tube system uses an orifice tube in place of the expansion valve. The accumulator (5) and the in-line dryer with orifice tube (3) replace the receiver-dryer.

The orifice tube assembly (7) is located in one end of the in-line dryer (3). The in-line dryer (3) is located in the line that goes from the condenser coil (2) to the evaporator coil (4). Quick couplers enable the in-line dryer (3) to be replaced without recovering the system. (6) .

Note: The dryer (3) should be replaced annually. The dryer should also be replaced whenever the system is opened.

In models without an in-line dryer, the desiccant is located in the accumulator (5). The accumulator is located in the line that extends from the evaporator coil (4) to the compressor (1). The orifice tube assembly (7) is located at the evaporator inlet tube.


NOTICE

The orifice tube systems do not have a sight glass for determining whether the system is low on refrigerant.


Orifice Tube



Illustration 3 g00364412

Typical Orifice Tube Assembly

(7) Orifice tube assembly

(10) Orifice tube

(11) O-Ring seal

(12) Tab

(13) Screens

The orifice tube assembly (7) has a plastic body, two screens (13) and a small brass tube (10) that is located in the center of the body. The O-Ring seals (11) are positioned on the body of the orifice tube to seal against leakage. If the system has an in-line dryer, orifice tube assembly (7 ) is contained in the dryer. If the system does not have an in-line dryer, orifice tube assembly (7) is located at the evaporator inlet tube. The orifice tube assembly is used in place of the thermostatic expansion valve.

The orifice tube assembly (7) changes the refrigerant from a high pressure and high temperature refrigerant into a low pressure and low temperature liquid. The orifice tube (10) has a restriction. The restriction in the orifice tube assembly allows the liquid refrigerant to be reduced from a high pressure to a low pressure. The flow rate is controlled by pressure differences across the orifice. The flow rate is also controlled by the temperature of the liquid refrigerant that is in the bottom of the condenser. The flow rate is sensitive to temperature differences and pressure differences. The flow rate is more sensitive to temperature differences.

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